Building a Testable Data Building a Testable Data Access LayerAccess LayerTodd AnglinTodd AnglinChief Evangelist, Telerik

Level: Intermediate

IntroductionsIntroductions

Todd Anglin

Chief Evangelist, TelerikMicrosoft MVP

ASP InsiderPresident NHDNUG & O’Reilly Author

@toddanglin

TelerikWatch.com

today’s plantoday’s plan

what is a “data layer”?what is a “data layer”?

PresentationPresentation

Data LayerData Layer

Responsible for talking to “persistence layer”

Web Desktop

Domain Logic(“the code that makes you money”)

Domain Logic(“the code that makes you money”)

Data / ModelData / Model

PersistencePersistence

Database Cloud XML Etc.

ServiceService

why build a data layer?why build a data layer?what’s the benefit?

importance of data layerimportance of data layer

• Decouple application from persistence= easier maintenance

= improved testability

= greater reusability

PresentationPresentation

Web Desktop

Domain Logic(“the code that makes you money”)

Domain Logic(“the code that makes you money”)

DataData

PersistencePersistence

Database Cloud XML Etc.

ServiceService

a a goodgood data layer… data layer…

1. Handles all data access

2. Hides implementation

3. Flexible– Easy to refactor

a a badbad data layer is… data layer is…

1. Does not centralize data access

2. Makes application very dependent on persistent store

3. Easy*

how do we build “data layers”?how do we build “data layers”?

By Hand

Pros-POCO-YAGNI-No-RTFMCons-Time-No FM

By Hand

Pros-POCO-YAGNI-No-RTFMCons-Time-No FM

ORM

Pros-Time-FlexibleCons-Learning-Limits-Trust*

ORM

Pros-Time-FlexibleCons-Learning-Limits-Trust*

popular .NET ORMspopular .NET ORMs

DEMODEMOBuild data layer with LinqToSql & EF & OpenAccess

data layer patternsdata layer patterns

• Domain Driven Design (DDD)– Key concepts: Repositories act on model

• ActiveRecord– Key concepts: Model objects act on themselves

• Data Mapper– Key concepts: Objects mapped to tables

DEMODEMOAdd data access pattern to project

testing the data layer

two testing campstwo testing camps

A Test Database B Mock

Database

Concepts:•Test against “real” database•Use set-up/tear-down code to create test data

Good When…You put lots of logic in your database

Concepts:•Test against “fake” database•Isolates your code from database behavior

Good When…You want fast unit tests and you put most logic in code

Mocking

Pros-Unit test-Isolate concerns-FastCons-“Hides” issues-Does not test database logic

Mocking

Pros-Unit test-Isolate concerns-FastCons-“Hides” issues-Does not test database logic

“Test” Database

Pros-Catches more issues-FamiliarCons-Slow-Not a “unit” test

“Test” Database

Pros-Catches more issues-FamiliarCons-Slow-Not a “unit” test

picking a camppicking a camp

UNIT TEST“Isolated. Repeatable. Fast.”

INTEGRATION TEST“Test interaction between units.”

FUNCTIONAL TEST“Test behavior from user perspective.”

mock testingmock testing

Goal: Test your business logic

B

Database Communication(ORM, ADO.NET, etc.)

Database Communication(ORM, ADO.NET, etc.)

RepositoryRepository

Business CodeBusiness Code

UI BehaviorsUI Behaviors ServicesServices

DatabaseDatabase

mockingmocking

• Stunt doubles for real objects– Look the same on the outside

Mocking Tools:JustMock (by Telerik)Isolator (by TypeMock)

MOQ (OSS)RhinoMocks (OSS)

AAA mocking patternAAA mocking pattern

//Arrange

Set-up your test variables and mocks

//Act

Execute your code like normal

//Assert

Verify what happened

DEMO: MOCKING DEMO: MOCKING DATABASEDATABASE

Testing L2S with Mock Objects

test databasetest database

Goal: Test your business logic + database behavior

A

Steps for every test:1.Create database schema + test data2. (Optional) Test database setup

correctly3.Execute unit test code4.Verify database behaved correctly

hard partshard parts

1. Creating test schema/data– DbUnit

2. Speed– In memory database

– SQL Lite, SQL CE, etc.

rules for test database testsrules for test database tests

1. Prior to running tests, schema should be redeployed to test DB (+ test data)

2. Tests should not change existing data– Edits, Deletes should be on records created by test

– Original data should be read-only

3. Tests should not depend on changes from previous tests

DEMO: TESTING WITH DEMO: TESTING WITH REAL DBREAL DB

Creating integration tests to talk to real database

should you test your DAL?should you test your DAL?

anglin@telerik.com@toddanglin

telerikwatch.com

Q&A

LinksLinks• 4GuysFromRolla on Testing DAL (2005)

– http://aspnet.4guysfromrolla.com/articles/040605-1.2.aspx

• Unit Testing the DAL (Java, but great discussion of DAL data testing)– http://www.buunguyen.net/blog/unit-testing-the-data-access-layer.html

• Roy Osherove on using Mocks for DAL testing– http://weblogs.asp.net/rosherove/archive/2003/09/30/29734.aspx

• SQL Lite project page– http://www.sqlite.org/docs.html– System.Data.SQLite: http://sqlite.phxsoftware.com/– http://www.mikeduncan.com/sqlite-on-dotnet-in-3-mins/– http://hendryluk.wordpress.com/2008/10/07/data-access-test-with-sqlite/

• DbUnit.NET (last updated 2006 – still alpha)– http://dbunit-net.sourceforge.net/GettingStarted.html

• SQL Server Compact 4 CTP1 (2010)– http://www.microsoft.com/downloads/details.aspx?FamilyID=0d2357ea-324f-46fd-88fc-7364c80e4fdb&displaylang=en– http://robtiffany.com/sql-server-compact/here-comes-sql-server-compact-4-0

• SQL Script to clear all tables in database– http://www.smallworkarounds.net/2009/02/script-to-delete-all-data-from-sql.html

• Microsoft.SqlServer.Management.Smo primer– http://davidhayden.com/blog/dave/archive/2006/01/27/2774.aspx– http://social.msdn.microsoft.com/Forums/en-US/adodotnetdataproviders/thread/43e8bc3a-1132-453b-b950-09427e970f31

• Multi-tier L2S architecture ideas– http://blog.stevensanderson.com/2007/11/29/linq-to-sql-the-multi-tier-story/