What is Entity Framework

8/9/2019 What is Entity Framework

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What is Entity Framework?First question that comes to the mind is what is an entity framework?

Microsoft has given following definition:

The Microsoft ADO.NET Entity Framework is an Object/Relational Mappin !ORM" framework thatenables #e$elopers to work with relational #ata as #omain%specific objects& eliminatin the nee# formost of the #ata access pl'mbin co#e that #e$elopers 's'ally nee# to write. (sin the EntityFramework& #e$elopers iss'e )'eries 'sin *+N,& then retrie$e an# manip'late #ata as stron ly type#objects. The Entity Framework-s ORM implementation pro$i#es ser$ices like chan e trackin & i#entityresol'tion& la y loa#in & an# )'ery translation so that #e$elopers can foc's on their application%specific b'siness lo ic rather than the #ata access f'n#amentals.

To simply say it: Entity framework is an Object/ elational Ma!!ing "O/ M# framework$ %t is anenhancement to &'O$(E) that gives develo!ers an automated mechanism for accessing * storing the

data in the database and working with the results in addition to 'ata eader and 'ata+et$

(ow the question is what is O/ M framework and why do we need it?

O M is a tool for storing data from domain objects to relational database like M+ +,- +erver in anautomated way without much !rogramming$ O/ M includes three main !arts: 'omain class objects.

elational database objects and Ma!!ing information on how domain objects ma!s to relational databaseobjects "tables. views * stored!rocedures#$ O M hel!s us to kee! our database design se!arate from our

domain class design$ )his makes a!!lication maintainable and e tendable$ %t also automates standard0 1' o!eration "0reate. ead. 1!date * 'elete# so develo!er doesn2t need to write it manually$

For more info visit: htt!://en$wiki!edia$org/wiki/Object3relational4ma!!ing

)here are many O M frameworks for $net in the market like 'ataObjects$(et. (5ibernate. O!en&ccess.+ub+onic etc$ Entity Framework is an o!en source O M framework from Microsoft$

Entity Framework ArchitectureFollowing figure shows the overall architecture of the Entity Framework$ -et2s see each com!onent of thearchitecture:

http://en.wikipedia.org/wiki/Object-relational_mappinghttp://en.wikipedia.org/wiki/Object-relational_mapping


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EDM (Entity Data Model): E'M consist three main !arts3 0once!tual model. Ma!!ing and +toragemodel$

Conceptual Model: 0once!tual model is your model classes and their relationshi!s$ )his will beinde!endent from your database table design$

tora!e Model: +torage model is your database design model which includes tables. views. stored !rocedures and their relationshi!s and keys$

Mappin!: Ma!!ing consist information about how your conce!tual model is ma!!ed to storage model$

"#$% to Entities: -%(, to Entities is query language used to write queries against the object model$ %treturns entities which are defined in the conce!tual model$ 6ou can use your -%(, skills here$

Entity %": Entity +,- is again a query language same as -%(, to Entities$ 5owever it is little moredifficult than -7E and also develo!er need to learn it se!arately$


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&' ect er ice: Object service is a main entry !oint for accessing data from database and to return it back$ Object service is res!onsible for materiali8ation which is !rocess of converting data returned fromentity client data !rovider "ne t layer# to an entity object structure$

Entity Client Data *ro ider: )he main res!onsibility of this layer is to convert -7E or Entity +,-queries into +,- query which is understood by underlying database$ %t communicates with &'O$(et data !rovider which in turn sends or retrieves data from database$

AD&+$et Data *ro ider: )his layer communicates with database using standard &'O$(et$

Setup EntityFramework Environment:%nstall the following for the basic tutorials:

• .NET Framework 4.5/Visual Stu io !"#!

• $S S%& Server !""5/!""'/!"#! E(press

Setting up the database

)his tutorial will use sam!le +chool'9 which has different tables. stored !rocedures and view$

Following is +chool'9 database design:


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• One-to-One: Stu ent an Stu ent) ress *as one+to+one relations*ip eg. Stu ent*as ,ero or one Stu ent) ress.

• One-to-Many: Stan ar an Tea-*er *as one+to+many relations*ip eg. many Tea-*ers -an e asso-iate wit* one Stan ar .

• Many-to-Many: Stu ent an ourse *as many+to+many relations*ip using

Stu ent ourse ta le w*ere Stu ent ourse ta le in-lu es Stu ent0 an ourse0 . Soone stu ent -an 1oin many -ourses an one -ourse also -an *ave many stu ents.

+am!le !roject contains +chool'9$mdf which you can attach to your local +,- server 7 ; database$

reate Entity 2ata $o el in EntityFramework 5."


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5ere. we are going to create Entity 'ata Model "E'M# for +chool'9 database and understand basic building blocks$

6ou can create entity data model for e isting database in Entity Framework ;$ the same way as youcreated it in Entity Framework


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>$ Entity 'ata Model Bi8ard in +7 =7 o!ens with four o!tions to select$ EF Desi!ner ,rom data'ase isfor database first a!!roach. Empty EF Desi!ner model for model first a!!roach. Empty Code Firstmodel and Code First ,rom data'ase is for code first a!!roach$ Be will focus of database first a!!roachin the basic tutorials so select EF Desi!ner ,rom data'ase o!tion and click $e-t


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;$ %n this ste!. you need to choose the version of Entity Framework$ Be will use Entity Framework ;$ inthe basic tutorials so select Entity Framework ;$ and click (e t$


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C$ )his ste! will dis!lay all the )ables. iews and +tored Drocedures in the database$ +elect tables. views

and +Ds you want. kee! the default checkbo es selected and click Finish$ 6ou can change Model (ames!ace if you want$

$ote:

*lurali.e or sin!ulari.e !enerated o' ect names checkbo singulari8e entityset name if table name inthe database is !lural eg$ %f +chool'9 has +tudents table name then entityset would be singular +tudent$+imilarly relationshi!s between the model will be !lurali8e if table has one3to3many or many3to3manyrelationshi! with other table$ Eg$ +tudent has many3to3many relationshi! with course table so +tudententity set will have !lural !ro!erty name 0ourses for the collection of courses$

second checkbo . #nclude ,orei!n key columns in the model includes foreign key !ro!erty e !licitly tore!resent the foreign key$ For e am!le. +tudent table has one3to3many relationshi! with +tandard table$+o every student is associated with only one standard$ )o re!resent this in the model. +tudent entitysetincludes +tandard%d !ro!erty with +tandard navigation !ro!erty$ %f this checkbo is unchecked then it willonly include +tandard !ro!erty but not +tandard%d in +tudent entityset$

)hird checkbo . #mport selected stored procedures and ,unctions into entity model automaticallycreates Function %m!orts for the stored !rocedures and functions$ 6ou don2t need to manyally im!ort it asyou had to do it !rior to Entity Framework ;$ $


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$ &fter clicking on AFinish2. it will add +chool$edm file into your !roject$

O!en E'M designer by double clicking on +chool$edm that dis!lays all the entities for selected tablesand relation between them as below:


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+o this way you can create sim!le E'M from your e isting database$

(ow let2s see all the building blocks of generated E'M "+chool$edm # as shown in above figure$

Entity/Ta'le Mappin!:

Each entity in E'M is ma!!ed with database table$ 6ou can check entity3table ma!!ing by right click onany entity in the E'M designer 3@ select )able Ma!!ing$ &lso. if you change any !ro!erty name of entityfrom designer then table ma!!ing would reflect that automatically$


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Conte-t 0 Entity Classes:

Every Entity 'ata Model generates one conte t class and multi!le entity classes for each '9 table$E !and +chool$edm and see two im!ortant files. GE'M (ameH$0onte t$tt and GE'M (ameH$tt:


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chool+Conte-t+tt: )his )< tem!late file generates conte t class whenever you change Entity 'ata Model"$edm file#$ 6ou can see conte t class file by e !anding +chool$0onte t$tt$ 0onte t class resides inGE'M (ameH$conte t$cs file$ 'efault conte t class name is G'9 (ameH I Entities eg$ 0onte t classname for our +chool'9 is +chool'9Entities$ 0onte t class is derived from '90onte t class in EntityFramework ;$ $ Drior to EF ;$ . it used to derive from Object0onte t$


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chool+tt: +chool$tt is )< tem!late file that generates entity classes for each '9 tables$ Entity classes areDO0O "Dlain Old 0- Object# classes that can be !ro y classes "we will see later what is !ro y classes#$

EDM Desi!ner: E'M designer re!resents your conce!tual model$ %t consist Entities. associations *multi!licity between the entities$ %nitially it will e actly look like your database table structure but youcan add or merge columns or remove columns which are not required by your a!!lication from thisdesigner$ Even you can add new object in this model which can have columns from different databasetables from conte t menu as shown in above figure$ emember. whatever changes you do here it should

be ma!!ed with storage model$ +o you have to be careful while doing any changes in the designer$

6ou can o!en this E'M designer in JM- view where you can see all the three !art of E'M3 0once!tualschema "0+'-#. +torage schema "++'-# and ma!!ing schema "M+-#. together in JM- view$


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ight click on +chool$edm 3@ click AO!en with$$2. this will o!en !o!u!$ +elect AJM- "te t# Editor2 in the !o!u!$ isual +tudio cannot dis!lay the model in 'esign view and in JM- at the same time. so you willsee a message asking whether it2s OK to close the 'esign view of the model$ 0lick 6es$ )his will o!enJM- view$ 6ou can see following JM- view by toggling all outlining

6ou can see ++'- content. 0+'- content and 03+ ma!!ing content here$ %f you e !and ++'- and0+'-. each one has some common JM- node under each schema node$ 6ou don2t need to edit ml

because you can do it in the Model 9rowser$

Model 1rowser: O!en Model 9rowser by right clicking on the E'M 'esigner and select Model 9rowser from conte t menu:

Model browser contains all the information about the E'M. its conce!tual model. storage model andma!!ing information$


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EntityContainer Entity0ontainer is a wra!!er for Entity+ets and &ssociation+ets$ %t is critical entry !ointfor querying the model$

Entity et: Entity+et is a container for Entity)y!e$ %t is set of same entityty!e$ 6ou can think it like dbtable$


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EntityType: Entity)y!e is a dataty!e in the model$ 6ou can see each Entity)y!e for your conce!tualmodel in JM-$ %f you e !and Entity)y!e node in JM-. you can see each !ro!erties and its ty!e andother info$

Association et: &ssociation+et defines the relation between each Entity+et$

Types o, Entity in Entity Framework:)here was four ty!es of Entities in Entity Framework # DO0O Dro y"dnamic !ro y#


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DO0O entity should meet the following requirement to become DO0O !ro y:

=$ & custom data class must be declared with !ublic access$

7$ & custom data class must not be sealed "(ot%nheritable in isual 9asic#

>$ & custom data class must not be abstract "Must%nherit in isual 9asic#$


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Netting the actual entity ty!e from a dynamic !ro y:

6ou can use Object0onte t$NetObject)y!e"# to find actual ty!e of dynamic !ro y as below:

Entity can have two ty!es of !ro!erties. +calar !ro!erties and (avigation !ro!erties$

calar properties are !ro!erties whose actual values are contained in the entity$ For e am!le. +tudententity has scalar !ro!erties e$g$ +tudent%d. +tudent(ame$ )hese corres!onds with the +tudent tablecolumns$

$a i!ation properties are !ointers to other related entities$ )he +tudent has +tandard !ro!erty asnavigation !ro!erty that will enable a!!lication to navigate from a +tudent to related +tandard entity$

%uerying wit* E2$:6ou can query E'M mainly by three ways. =# -%(, to Entities 7# Entity +,- ># (ative +,-

3) "#$% to Entities: -7E query synta is easier to learn than Entity +,-$ 6ou can use your -%(, skillsfor querying with E'M$ )here are two ty!es of synta you can use with -%(,3to3Entities. -%(, Method+ynta with -amda e !ression and -%(, query synta $

"#$% Method synta-(lamda e-pression):


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&&'uer ing #it LIN' to ntities

using (%ar conte*t " ne# Sc oolD+ ntities()) { %ar L, 'uer " conte*t!Students!# ere(s "> s!StudentName "" -+ill.); } "#$% %uery synta-:

using (%ar conte*t " ne# Sc oolD+ ntities())

{ %ar L, 'uer " /rom st in conte*t!Students # ere st!StudentName "" 0+ill0 select st; }First. you have to create object of conte t class which is +chool'9Entities$ 6ou should initiali8e it inusing"# so that once it going out of using sco!e then it will automatically call 'is!ose"# method of'b0onte t$ %n both the synta above. conte t returns %,ueryable$

Be will learn different ty!es of -%(, to Entities query in !rojection query cha!ter later$

4) Entity %": Entity +,- is another way to create a query$ %t is !rocessed by the Entity Framework2sObject +ervices directly$ %t returns Object,uery instead of %,ueryable$

6ou need Object0onte t to create query using Entity +,-$

Following -o e snippet s*ows same 3uery result as &!E 3uery a ove.

&&'uer ing #it 1b2ect Ser%ices and ntit S'L string s3lString " 0S L C4 5AL6 st 7819 Sc oolD+ ntities!Students 0 : 0AS st $ 8 st!StudentName "" +ill 0;

%ar ob2ct* " (ct* as I1b2ectConte*tAdapter)!1b2ectConte*t;

1b2ect'uer student " ob2ct*!Create'uer (s3lString); Student ne#Student " student!7irst();

ou -an also use Entity onne-tion an Entity omman to e(e-ute Entity S%& as elow:

using (%ar con " ne# ntit Connection(0name"Sc oolD+ ntities0)) { con!1pen(); ntit Command cmd " con!CreateCommand(); cmd!Command4e*t " 0S L C4 5AL6 st 7819 Sc oolD+ ntities!Students as st # erest!StudentName" +ill 0; Dictionar dict " ne# Dictionar ();


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$o el First evelopment wit* EntityFrameworkModel First: %n Model First a!!roach. you create Entities. relationshi!s. and inheritance hierarchies

directly on the design surface of E'MJ$ +o in Model First a!!roach. when you add &'O$(E) Entity'ata Model. you should select Empty EF Desi!ner model $

6ou can create entity. association and inheritance on em!ty designer using toolbo $


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&fter creating required entities. associations and inheritance on design surface of the em!ty model. youcan use designer2s conte t menu o!tion Nenerate database from model to generate ''- scri!t$

+elect e isting database connection from wi8ard and then it will dis!lay ''- for the entities$


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+o this is called Model First a!!roach$

2ata ase First evelopment wit* EntityFramework 4."Be have already seen this a!!roach in 0reate Entity 'ata Model where we created model and classesfrom e isting database$ +o when you generate E'MJ from e isting database then it is a 'atabase Firsta!!roach$

http://www.entityframeworktutorial.net/EntityFramework5/create-dbcontext-in-entity-framework5.aspxhttp://www.entityframeworktutorial.net/EntityFramework5/create-dbcontext-in-entity-framework5.aspxhttp://www.entityframeworktutorial.net/EntityFramework5/create-dbcontext-in-entity-framework5.aspx


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Eager &oa ing:Eager loading is the !rocess whereby a query for one ty!e of entity also loads related entities as !art ofthe query$ Eager loading is achieved using #nclude method of %,ueryable$

9elow code sni!!et shows eager loading where +tandard entity will also be loaded with +tudent entityusing %nclude method:

L !" "ue#y Synta$:

using (%ar conte*t " ne# Sc oolD+ ntities()) { %ar res " (/rom s in conte*t!Students!Include(0Standard0) # ere s!StudentName "" 0StudentB0 select s)!7irst1rDe/ault(); }

L !" Method Synta$:

using (%ar ct* " ne# Sc oolD+ ntities()) { stud " ct*!Students!Include(s "> s!Standard) ! ere(s "> s!StudentName ""0StudentB0)!7irst1rDe/ault();

&& ou can also pass entit name as a string 0Standard0 && stud " ct*!Students!Include(0Standard0) ! ere(s "> s!StudentName ""0StudentB0)!7irst1rDe/ault(); } &bove code will result in following +,- query:

S L C4 41 (B)*tentBE! StudentIDE AS StudentIDE=*tentBE! StudentNameE AS StudentNameE=*tent,E! StandardIdE AS StandardIdE=*tent,E! StandardNameE AS StandardNameE=*tent,E! DescriptionE AS DescriptionE

7819 dboE! StudentE AS *tentBE L 74 164 8 F1IN dboE! StandardE AS *tent,E 1N *tentBE! StandardIdE "

*tent,E! StandardIdE $ 8 StudentB " *tentBE! StudentNameE "oad multiple le els o, related entities:


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6ou can also eagerly load multi!le levels of related entities$ 9elow code sni!!et loads related +tudent.+tandard and )eachers:

using (%ar ct* " ne# Sc oolD+ ntities())

{ stud " ct*!Students! ere(s "> s!StudentName "" 0StudentB0) !Include(s "> s!Standard!4eac ers)!7irst1rDe/ault(); } &bove code results in following +,- query:

S L C4 ro2ect,E! StudentIDE AS StudentIDE=

ro2ect,E! StudentNameE AS StudentNameE=ro2ect,E! StandardIdE AS StandardIdE=ro2ect,E! StandardNameE AS StandardNameE=ro2ect,E! DescriptionE AS DescriptionE=ro2ect,E! CBE AS CBE=ro2ect,E! 4eac erIdE AS 4eac erIdE=ro2ect,E! 4eac erNameE AS 4eac erNameE=ro2ect,E! StandardIdBE AS StandardIdBE

7819 ( S L C4LimitBE! StudentIDE AS StudentIDE=LimitBE! StudentNameE AS StudentNameE=LimitBE! StandardIdBE AS StandardIdE=LimitBE! StandardNameE AS StandardNameE=LimitBE! DescriptionE AS DescriptionE=

ro2ectBE! 4eac erIdE AS 4eac erIdE=ro2ectBE! 4eac erNameE AS 4eac erNameE=ro2ectBE! StandardIdE AS StandardIdBE=

CAS $ N ( ro2ectBE! 4eac erIdE IS N6LL) 4$ N CAS4(N6LL AS int) LS B NDAS CBE 7819 (S L C4 41 (B) *tentBE! StudentIDE AS StudentIDE= *tentBE!

StudentNameE AS StudentNameE= *tentBE! StandardIdE AS StandardId,E= *tent,E!StandardIdE AS StandardIdBE= *tent,E! StandardNameE AS StandardNameE= *tent,E!DescriptionE AS DescriptionE

7819 dboE! StudentE AS *tentBE L 74 164 8 F1IN dboE! StandardE AS *tent,E 1N *tentBE! StandardIdE "

*tent,E! StandardIdE $ 8 updated student " *tentBE! StudentNameE ) AS LimitBE L 74 164 8 F1IN (S L C4

*tent@E! 4eac erIdE AS 4eac erIdE=*tent@E! 4eac erNameE AS 4eac erNameE=*tent@E! StandardIdE AS StandardIdE

7819 dboE! 4eac erE AS *tent@E $ 8 *tent@E! StandardIdE IS N14 N6LL ) AS ro2ectBE 1N LimitBE!

StandardId,E " ro2ectBE! StandardIdE ) AS ro2ect,E 18D 8 +G ro2ect,E! StudentIDE ASC= ro2ect,E! StandardIdE ASC= ro2ect,E! CBEASC

"a.y "oadin!:One of the im!ortant functionality of Entity Framework is la8y loading$ -a8y loading means delaying theloading of related data until you s!ecifically request it$ For e am!le. +tudent class contains+tudent&ddress as com!le !ro!erty$ +o conte t first loads all the students from the database then it willload address of !articular student when we access +tudent&ddress !ro!erty as below$


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using (%ar ct* " ne# Sc oolD+ ntities()) { ct*!Con/iguration!LaH Loading nabled " true;

&&Loading students onl IList studList " ct*!Students!4oList();

Student std " studList E;

&&Loads Student address /or particular Student onl (seperate S'L 3uer ) StudentAddress add " std!StudentAddress; }

&bove code will result in two +,- query$ First. it will fetch all students:

S L C4*tentBE! StudentIDE AS StudentIDE=*tentBE! StudentNameE AS StudentNameE=*tentBE! StandardIdE AS StandardIdE

7819 dboE! StudentE AS *tentBE

&nd then sends following query when we get the reference of +tudent&ddress:

e*ec sp e*ecutes3l N S L C4

*tentBE! StudentIDE AS StudentIDE=*tentBE! AddressBE AS AddressBE=*tentBE! Address,E AS Address,E=*tentBE! Cit E AS Cit E=*tentBE! StateE AS StateE

7819 dboE! StudentAddressE AS *tentBE $ 8 *tentBE! StudentIDE " J ntit Ke 5alueB =N J ntit Ke 5alueB

int =J ntit Ke 5alueB"B

5owever. you can also turn off la8y loading for !articular !ro!erty or entire conte t$ )o turn off la8yloading for !articular !ro!erty. do not make it virtual$ )o turn off la8y loading for all entities in theconte t. set its configuration !ro!erty to false:

public Sc oolD+ ntities() base(0name"Sc oolD+ ntities0)

{ t is!Con/iguration!LaH Loading nabled " /alse; }

2ules ,or la.y loadin!:

=$ context.Configuration.ProxyCreationEnabled should be true$

7$ context.Configuration.LazyLoadingEnabled should be true$


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>$ 0om!le !ro!erty should be defined as virtual$ 0onte t will not do la8y loading if the !ro!erty isnot define as virtual$

E(pli-it &oa ing wit* 2 onte(t

Even with la8y loading disabled it is still !ossible to la8ily load related entities. but it must be done withan e !licit call$ 1se -oad method of '9EntityEntry object$

Following code e !licitly loads +tandard of !articular +tudent using eference"# method of'bEntityEntry:


{ &&Disable LaH loading

conte*t!Con/iguration!LaH Loading nabled " /alse; %ar student " (/rom s in conte*t!Students

# ere s!StudentName "" 0+ill0 select s)!7irst1rDe/ault();

conte*t! ntr (student)!8e/erence(s "> s!Courses)!Load(); }%f you run above code. you can see that first it loads student but not standard as below:

-oad method get +tandard entity as below:


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&bove code e ecute two different database queries$ First query is to get +tudent and second query to getstandard$

"oad collection:

1se collection method instead of eference method to load collection navigation !ro!erty$ Followinge am!le loads courses of student$


{ conte*t!Con/iguration!LaH Loading nabled " /alse;

%ar student " (/rom s in conte*t!Students # ere s!StudentName "" 0+ill0 select s)!7irst1rDe/ault();

conte*t! ntr (student)!Collection(s "> s!Courses)!Load(); }

$ote: The "oad e-tension method works ust like To"ist e-cept that it a oids the creation o, the listalto!ether+


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D1Conte-t:&s you have seen in !revious cha!ter. E'M generates 0onte t class and Entity classes$ )his conte t classis derived from System.Data.Entity.DbContext class$

'b0onte t is a !rimary class that is res!onsible for interacting with data as object$ %t often referred to asconte t$ %t does following activities:

• %ueryin!: %t can be useful in querying the database$ %t converts database values into entityobjects and vica versa$

• Chan!e Trackin!: %t kee!s track of changes occurred in the entities after it has been queryingfrom the database$

• *ersistin! Data: %t also !erform %nsert. u!date and delete o!eration to the database based on theentity states$

Drior to EntityFramework


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*u'lic Methods:

Method!a%e

&etu#n 'ype (es)#iption *$a%p+e

Entry67 1e-t8

DBEntityEntry 9ets a2 EntityEntryo 1e-t or t*egiven entityprovi inga--ess toin ormationa out t*eentity an t*ea ility toper orm a-tionson t*e entity.

Entry met*o returns 2 EntityEntry o 1e-t opasse entity o 1e-t t*roug* w*i-* we -an-*ange its state; -urrentValues anoriginalValues.

t(.Entry6Stu entEntity8.State <System.2ata.EntityState.$o i=e >

t(.Entry6Stu entEntity8. urrentValues.SetValues6Stu entEntity2T78>

t(.Entry6Stu entEntity8.7riginalValues.SetValues6Stu entEntity2T78>

Entry?TEntity@6

TEntity8

2 EntityEntry? TEntity@

9ets a2 EntityEntry?

TEntity@ o 1e-tor t*e given

entity provi inga--ess toin ormationa out t*eentity an t*ea ility toper orm a-tionson t*e entity.

Same as Entry met*o ut t*is generi- met*ooes type -*e-k o passe Entity7 1e-t e ore

returning DBEntityEntry o 1e-t

Set6Type8 DBSet Aeturns a2 Set or t*espe-i=e type;t*is allows

AB2operations to

e per ormeor t*e given

entity in t*e-onte(t.

AB2 operation.

-t(.Set6stu .9etType68. aseType8.) 6stu entEntity8>-t(.Set6stu .9etType68. aseType8.)tta-*6stu entEntity8>-t(.Set6stu .9etType68. aseType8.Aemove6stu entEntity8>

var result <-t(.Set6stu entEntity.9etType68. aseType8.S3l%uery6Csele-t D rom stu entC8>

stu entEntity.9etType68 will return P7 7 Pro(ytype.stu entEntity.9etType68. aseType s*oul e useto get an a-tual entity type.


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Set?TEntity@68

2 Set Aeturns a2 Set or t*espe-i=e type;t*is allows

AB2operations to

e per ormeor t*e givenentity in t*e-onte(t.

AB2 operation.

-onte(t.Set?Stu ent@68.) 6stu entEntity8>-onte(t.Set?Stu ent@68.)tta-*6stu entEntity8

>-onte(t.Set?Stu [email protected] entEntit

y8>var result < -onte(t.Set68.S3l%uery6Csele-t Drom stu entC8>

Save *anges68

int Saves all-*anges ma ein t*is -onte(tto t*eun erlying

ata ase.

Save -*anges to t*e ata ase:

2 -onte(t.Save *anges68>

*rotected Methods:

Method !a%e &etu#n 'ype (es)#iption

S*oul Vali ateEntity

bool E(tension point allowing t*e user to overri e t*ee ault e*avior o vali ating only a e an

mo i=e entities.

Vali ateEntity 2 EntityVali ationAesult

E(tension point allowing t*e user to -ustomi,evali ation o an entity or =lter out vali ation results.

alle y 9etVali ationErrors68.

*u'lic *roperties:

,#ope#ty!a%e

&etu#n 'ype (es)#iption

*angeTra-ker

DBChangeTracker Provi es a--ess to eatures o t*e -onte(t t*at eal wit*-*ange tra-king o entities.

on=guration

2 onte(t on=guration

Provi es a--ess to -on=guration options or t*e -onte(t.

2ata ase Database reates a ata ase instan-e or t*is -onte(t an allows

you to per orm -reation; eletion or e(isten-e -*e-ks ort*e un erlying ata ase.

isit M+'( for more information of '90onte t class$

http://msdn.microsoft.com/en-us/library/system.data.entity.dbcontext(v=vs.103).aspxhttp://msdn.microsoft.com/en-us/library/system.data.entity.dbcontext(v=vs.103).aspxhttp://msdn.microsoft.com/en-us/library/system.data.entity.dbcontext(v=vs.103).aspxhttp://msdn.microsoft.com/en-us/library/system.data.entity.dbcontext(v=vs.103).aspx


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Persisten-e in Entity Framework-earn how to !ersist an entity so that it either inserts new row or u!dates an e isting row or delete ane isting row in the database$

Be need to consider two scenarios. connected scenario and disconnected scenario$

Connected cenario: 0onnected scenario is when an entity is retrieved from the database and !ersistusing same conte t$ 0onte t object doesn2t destroy between when entity retrival and !ersistence$

(is)onne)ted S)ena#io: 2is-onne-te s-enario is w*en an entity is retrieve rom t*e

ata ase an mo i=e using i erent -onte(ts. 2is-onne-te s-enario is -omple( e-ausenew -onte(t oesn t know anyt*ing a out mo i=e entity so you *ave to tell -onte(t t*atw*at *as -*ange in entity. 0n t*e elow =gure; -lient retrieve entity grap* using onte(t #an t*en it per orm some B2 6-reate; up ate; 2elete8 operations an t*en it saves entitygrap* using onte(t !. onte(t ! oesn t know w*i-* operation *as een per orme on t*eentity grap* in t*is s-enario.


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C27D &peration in Connected cenario:

0 1' o!eration in connected scenario is fairly easy task because conte t automatically detact changesha!!ened in the entity !rovided &uto'etect0hangesEnabled is true by default$

Following e am!le show how you can add. u!date and delete entity using conte t and callconte t$+ave0hanges"# method to u!date the database$


{ %ar studentList " conte*t!Students!4oList();

&& er/orm create operation conte*t!Students!Add(ne# Student() { StudentName " 0Ne# Student0 });

&& er/orm 6pdate operation Student student4o6pdate " studentList! ere(s "> s!StudentName ""0studentB0)!7irst1rDe/ault(); student4o6pdate!StudentName " 0 dited studentB0;

&& er/orm delete operation conte*t!Students!8emo%e(studentList! lementAt( ));

&& *ecute Inser= 6pdate Delete 3ueries in t e database conte*t!Sa%eC anges(); }


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Student stud ;

&& ?et student /rom D+ using (%ar ct* " ne# Sc oolD+ ntities()) { stud " ct*!Students! ere(s "> s!StudentName "" 0Ne#StudentB0)!7irst1rDe/ault(); }

&& c ange student name in disconnected mode (out o/ D+Conte*t scope) i/ (stud O" null) { stud!StudentName " 06pdated StudentB0; }

&&sa%e modi/ied entit using ne# D+Conte*t using (%ar dbCt* " ne# Sc oolD+ ntities()) { &&9arP entit as modi/ied dbCt*! ntr (stud)!State " S stem!Data! ntit State!9odi/ied;

dbCt*!Sa%eC anges(); }

&s you see in the above code sni!!et. we are doing following ste!s:

=$ Net the e isting student

7$ 0hange student name out of '90onte t sco!e "disconnected mode#

>$ Be !ass modified entity into Entry method to get its '9EntityEntry object and then marking itsstate as Modified


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Be will see how to add single +tandard entity:

&& create ne# Standard entit ob2ect

%ar ne#Standard " ne# Standard();

&& Assign standard name ne#Standard!StandardName " 0Standard B0;

&&create D+Conte*t ob2ect using (%ar dbCt* " ne# Sc oolD+ ntities()) { &&Add standard ob2ect into Standard D+set dbCt*!Standards!Add(ne#Standard); && call Sa%eC anges met od to sa%e standard into database dbCt*!Sa%eC anges(); } &s you can see in above code sni!!et. first we have created new +tandard entity object and set

+tandard(ame to +tandard = $ +econd. created new '90onte t object and added newly created +tandardentity into +tandards Entity+et$ )hird. calling +ave0hanges method of '90onte t which sends insertquery to the database$

)his will result in following +,- query to the database:

e*ec sp e*ecutes3l N insert dboE! StandardE( StandardNameE= DescriptionE)

%alues (J = null) select StandardIdE /rom dboE! StandardE # ere JJ81 C16N4 > and StandardIdE " scope identit () =N J%arc ar(Q ) =J " Standard B &lternatively. we can also add +tandard entity into '90onte t$Entry and mark it as &dded which result insame insert query:

dbCt*! ntr (ne#Standard)!State " S stem!Data! ntit State!Added; +o this way you can add single entity$

%n the ne t cha!ter we will learn how to add entities which has one3to3one relationshi!$

2elete Entity using 2 onte(tBe used Entry"# method of 'b0onte t to mark Entity+tate to Modified in the !revious cha!ter$ +ame waywe can use Entry"# method to attach disconnected entity to the conte t and mark its state to 'eleted$


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{ conte*t! ntr (disconnected4eac er)!State " S stem!Data! ntit State!Deleted;

conte*t!Sa%eC anges(); }

&bove code results in following delete query which deletes the row from )eacher table$

delete dboE! 4eac erE # ere ( 4eac erIdE " J ) =N J int =J "B

on-urren-y in Entity Framework:Entity Framework su!!orts O!timistic 0oncurrency by default$ %n the o!timistic concurrency. EF savesthe entity to the database in the ho!e that the same data has not changed since the entity was loaded$ %f it

finds that data has changed then an e ce!tion is thrown and you must resolve the conflict beforeattem!ting to save it again$

-et s see how you can handle o!timistic concurrency with +tudent entity$

First of all. you need to have rowversion column in the +tudent table %n order to handle concurrency with+tuent entity$ owversion is is a dataty!e in +,- +erver that automatically generates unique binary

number whenever insert or u!date o!eration !erformed in a table$ )he rowversion dataty!e is just anincrementing number$ owevesion is synonym for the timestam! dataty!e$ 9oth are same$

0reate new column ow ersion in +tudent table with timestam! dataty!e as below:


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$ote: alue of ow ersion will be added and u!dated automatically by the databse in %nsert and1!dateo!eration$

(ow. create new Entity 'ata Model or u!date an e isting data model by right clicking on designer 3@7pdate Model From Data'ase 3@ efresh +tudent table$ +o now. you will see ow ersion !ro!ertyadded in the +tudent entity$

(ow. you need to a!!ly concurrency mode to ,i-ed by right clicking on 2ow8ersion !ro!erty in the+tudent entity "right click on ow ersion !ro!erty not +tudent entity# 3@ select Dro!erty$ 0hange0oncurrency Mode to Fi ed from (one in the !ro!erty window as below:

EF will now include ow ersion column in the where clause whenever you do u!date o!eration and ifrowversion value is different than in where clause then it will throw D'7pdateConcurrencyE-ection $

Following code shows that 1ser= and 1ser7 get the same student and u!date +tudent(ame at the sametime:

Student studentB it 6serB " null;Student studentB it 6ser, " null;

&&6ser B gets student using (%ar conte*t " ne# Sc oolD+ ntities()) { conte*t!Con/iguration! ro* Creation nabled " /alse;


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studentB it 6serB " conte*t!Students! ere(s "> s!StudentID ""B)!Single(); } &&6ser , also get t e same student using (%ar conte*t " ne# Sc oolD+ ntities()) { conte*t!Con/iguration! ro* Creation nabled " /alse; studentB it 6ser, " conte*t!Students! ere(s "> s!StudentID ""

B)!Single(); } &&6ser B updates Student name studentB it 6serB!StudentName " 0 dited /rom userB0;

&&6ser , updates Student name studentB it 6ser,!StudentName " 0 dited /rom user,0;

now. 1ser= saves his changes before 1ser7$ +o when user7 trys to save the changes. he will getconcurrency e ection:

&&6ser B sa%es c anges /irst

using (%ar conte*t " ne# Sc oolD+ ntities()) { tr { conte*t! ntr (studentB it 6serB)!State " ntit State!9odi/ied; conte*t!Sa%eC anges(); } catc (Db6pdateConcurrenc *ception e*) { Console! riteLine(01ptimistic Concurrenc e*ception occured0); } }

&&6ser , sa%es c anges a/ter 6ser B!&&6ser , #ill get concurrenc e*ection&&because Create1r9odi/iedDate is di//erent in t e databaseusing (%ar conte*t " ne# Sc oolD+ ntities())

{ tr { conte*t! ntr (studentB it 6ser,)!State " ntit State!9odi/ied; conte*t!Sa%eC anges(); } catc (Db6pdateConcurrenc *ception e*) { Console! riteLine(01ptimistic Concurrenc e*ception occured0); } }Concurrency in Code/First:

6ou can create timestam! !ro!erty in code3first by usng Q)imestam!R attribute$ Make sure !ro!erty ty!eis byteQR because timestam! is binary in 0S$

4imestampE

public b te E 8o#5ersion { get; set; }


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EF includes !ro!erty in where clause in u!date o!eration if the !ro!erty is marked with)imestam!attribute$

6ou can resolve concurrency e ection many ways$ isit msdn on detailed information on how to resolveo!timistic concurrency$

'ownload sam!le !roject for concurrency demo$

'ownload sam!le !roject for the demo$

Entity Framework 9+ #ntroduction:Belcome to Entity Framework C tutorials section$ 5ere. you will learn about new features introduced inEntity Framework C$ with isual +tudio 7 =7$

Entity Framework C$ has introduced many new e citing features for database first "designer# and code3first a!!roaches$

Features ,or Data'ase First (Desi!ner) and Code/First 1oth:

=$ 0onnection resiliency

7$ &synchronous query and save

>$ 0ode3based configuration


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==$ 0reating conte t with an o!en connection

=7$ %m!roved !erformance and warm3u! time

Features ,or Code/First:

=$ 0ustom conventions

7$ %nsert. u!date * delete stored !rocedures for entity 01' o!eration

>$ %nde attribute "EF C$=#


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Console! riteLine(07inis ed ?etStudent!!!0);

}

return student; }

&s you can see in the above code. Net+tudent method marked with async to make it asynchronous$eturn ty!e of asynchrounous method must be Task $ Net+tudent returns object of +tudent entity so returnty!e must be Task; tudent< $

&lso. query is marked with await . this freed calling thread to do something else till it e ecutes query andreturns data$ Be have used FirstOr'efault&sync e tension method of +ystem$'ata$Entity$ you may useother e tension methods a!!ro!riately like +ingleOr'efault&sync. )o-ist&syn etc$

Asynchronous a e:

6ou can call conte t$+ave0hanges asynchronously the same way as async query:

Transa-tion support:Entity Framework by default wra!s %nsert. 1!date or 'elete o!eration in a transaction whenever youe ecute +ave0hanges"#$ EF starts new transaction for each o!erations and com!lete the transaction whenit o!eration finishes$ Bhen you e ecute another such o!eration a new transaction is started$

EF C has introduced data'ase+1e!inTransaction and Data'ase+7seTransaction to !rovide more controlover transaction$ (ow. you can e ecute multi!le o!erations in a single transaction as below:

using (S stem!Data! ntit !DbConte*t4ransaction db4ran "conte*t!Database!+egin4ransaction( )) { tr { Student stdB " ne# Student() { StudentName " 0ne#student0 }; conte*t!Students!Add(stdB); conte*t!Database! *ecuteS3lCommand( J06 DA4 Student S 4 StudentName " dited Student Name 0 : 0 $ 8 StudentID "B0 ); conte*t!Students!8emo%e(stdB);

&&sa%es all abo%e operations #it in one transaction conte*t!Sa%eC anges();

&&commit transaction


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db4ran!Commit(); } catc ( *ception e*) { &&8ollbacP transaction i/ e*ception occurs db4ran!8ollbacP(); }

}database$1se)ransaction allows the 'b0onte t to use a transaction which was started outside of theEntity Framework$

2 Set.) Aange G 2 Set.AemoveAange:'b+et in EF C has introduced new methods &dd ange * emove ange$ 'b+et$&dd ange addscollection"%Enumerable# of entities to the 'b0onte t. so you don t have to add each entity individually$

IList ne#Students " ne# List(); ne#Students!Add(ne# Student() { StudentName " 0StudentB b addrange0 }); ne#Students!Add(ne# Student() { StudentName " 0Student, b addrange0 }); ne#Students!Add(ne# Student() { StudentName " 0Student@ b addrange0 });

using (%ar conte*t " ne# Sc oolD+ ntities()) { conte*t!Students!Add8ange(ne#Students); conte*t!Sa%eC anges(); }+ame way. use 'b+et$ emove ange to remove collection of entities from 'b+et$

IList e*istingStudents " M!!


{ conte*t!Students!8emo%e8ange(e*istingStudents); conte*t!Sa%eC anges(); }

ustom o e+First onventions:0ode First has a set of default behaviours for the models that refer to as conventions$ EF C !rovidesability to define your own custom conventions which will be default behaviour for your models$

)here are two main ty!es of 0onventions. 0onfiguration 0onventions and Model 0onventions$

Con,i!uration Con entions:


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0onfiguration 0onventions are a way to configure entities without overriding default behaviour !rovidedin the Fluent &D%$ 6ou can define a configuration convention inside your OnModel0reating event or in acustom 0onvention 0lass in a similar way to how you would define normal entity ma!!ings with theFluent &D%$

For e am!le. you can define !rimary key of entity that has !ro!erty named Gentity nameH 4%'$ E$g$+tudent4%' !ro!erty of +tudent entity will be !rimary key:

protected o%erride %oid 1n9odelCreating(Db9odel+uilder model+uilder) { model+uilder ! roperties() ! ere(p "> p!Name "" p!Declaring4 pe!Name : 0 ID0) !Con/igure(p "> p!IsKe ());

base!1n9odelCreating(model+uilder);

}Following e am!le show how to set string length of 'escri!tion !ro!erty in all entities:

protected o%erride %oid 1n9odelCreating(Db9odel+uilder model+uilder) { model+uilder ! roperties() ! ere(p "> p!Name "" 0Description0) !Con/igure(p "> p!$as9a*Lengt (, ));

base!1n9odelCreating(model+uilder); }6ou can also define custom class for this convention by deriving 0onvention class as below:

public class KCon%ention Con%ention { public KCon%ention() { ! roperties() ! ere(p "> p!Name "" p!Declaring4 pe!Name : 0 ID0) !Con/igure(p "> p!IsKe ());

} }0onfigure custom convention as below:

protected o%erride %oid 1n9odelCreating(Db9odel+uilder model+uilder)

{ model+uilder!Con%entions!Add< KCon%ention>(); }Model Con entions:


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Model 0onventions is based on the underlying model metadata$ )here are conventions for 0+'- and++'- both$ 0reate class that im!lements %0once!tualModel0onvention form 0+'- conventions andim!lement %+toreModel0onvention for ++'- convention$

isit code!le documentation for more information$

'ownload code3first sam!le !roject for custom conventions demo$

Code First / #nsert= 7pdate= Delete tored*rocedure Mappin!:Entity Framework C 0ode First !rovides ability to create and use stored !rocedure for add. u!date anddelete o!eration$ %t was not !ossible in the !revious versions of Entity Framework$

tudent Entity:

class Student { public Student() { }

public int Student ID { get; set; } public string StudentName { get; set; } }

Following e am!le automatically create stored !rocedure for +tudent entity using Fluent &D%$


{ model+uilder! ntit () !9ap4oStored rocedures(); }

&bove code will create three !rocedures +tudent4%nsert. +tudent41!date and +tudent4'elete$+tudent4%nsert and +tudent41!date stored !rocedures has !arameters name corres!onds to the !ro!ertynames$ +tudent4'elete will have !rimary key !ro!erty +tudent%' !arameter$

https://entityframework.codeplex.com/wikipage?title=Custom%20Conventionshttps://entityframework.codeplex.com/wikipage?title=Custom%20Conventionshttps://entityframework.codeplex.com/wikipage?title=Custom%20Conventionshttp://www.entityframeworktutorial.net/EntityFramework6/sample-project.aspxhttps://entityframework.codeplex.com/wikipage?title=Custom%20Conventionshttp://www.entityframeworktutorial.net/EntityFramework6/sample-project.aspx


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6ou can also change stored !rocedure and !arameters name as below:

protected o%erride %oid 1n9odelCreating(Db9odel+uilder model+uilder) { model+uilder! ntit () !9ap4oStored rocedures(p "> p!Insert(sp ">sp!$asName(0sp InsertStudent0)! arameter(pm "> pm!StudentName= 0name0)!8esult(rs ">rs!Student ID= 0Student ID0)) !6pdate(sp "> sp!$asName(0sp 6pdateStudent0)! arameter(pm ">pm!StudentName= 0name0)) !Delete(sp "> sp!$asName(0sp DeleteStudent0)! arameter(pm ">pm!Student ID= 0Id0)) ); }

%f you want all your entities to use stored !rocedures then do as following:


{

model+uilder!4 pes()!Con/igure(t "> t!9ap4oStored rocedures()); }

"imitations:

• Only Fluent &D% can be used to ma! stored !rocedures$ 6ou cannot use 'ata &nnotation attributesin EF C for stored !rocedure ma!!ing$

• 6ou cannot use mi ture of stored !rocedure and query to add. u!date and delete o!eration on thesame entity$ 6ou can either use stored !rocedure or +,- query for all add. u!date and deleteo!eration with entity$

'ownload sam!le !roject for demo$

isit code!le documentation for more information$

Previous

Ne(t

0n e( )ttri ute:

http://www.entityframeworktutorial.net/EntityFramework6/sample-project.aspxhttps://entityframework.codeplex.com/wikipage?title=Code%20First%20Insert%2FUpdate%2FDelete%20Stored%20Procedure%20Mappinghttps://entityframework.codeplex.com/wikipage?title=Code%20First%20Insert%2FUpdate%2FDelete%20Stored%20Procedure%20Mappinghttps://entityframework.codeplex.com/wikipage?title=Code%20First%20Insert%2FUpdate%2FDelete%20Stored%20Procedure%20Mappinghttp://www.entityframeworktutorial.net/EntityFramework6/sample-project.aspxhttps://entityframework.codeplex.com/wikipage?title=Code%20First%20Insert%2FUpdate%2FDelete%20Stored%20Procedure%20Mapping


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Entity Framework C !rovides %nde attribute to create %nde on !articular column in the database as below:

class Student { public Student()

{ }

public int Student ID { get; set; } public string StudentName { get; set; }

Inde*E public int 8egistrationNumber { get; set; } }9y default. %nde name will be %J4G!ro!erty nameH$ 5owever. you can also change %nde name$

6ou can also make it 0lustered inde by s!ecifying IsClustered = true and unique inde by s!ecifying IsUni ue=true $

Inde*( 0IND U 8 ?N690= IsClustered"true= Is6ni3ue"true )E public int 8egistrationNumber { get; set; }

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