FINAL REVIEWCIS266

Use the DataSet object

To transfer data between tiers To manipulate the data without an

open connection To relate data from multiple sources To bind data to a Windows form

Referring to Records, Fields Actual data values are held in

DataRow objects Each Table object in a dataset has a

DataRows collection made up of DataRow objects

Data values are held in the DataRow.Items collection Refer to fields by index position or by

name (string value)

Setting a Relationship

A DataRelation object describes the relationship between the tables.

Use the XML schema (.xsd) file for the dataset to create the relationship – or – use code to create a relation

DataRelation Object Functions Relating tables Setting up constraints

Retrieving Related Row(s)

Use the GetParentRow method to retrieve the matching row from the table on the one side

The GetChildRows method returns an array of rows from the many table May have 0, 1, or more related records

Use Find method to find a row by its primary key value

DataRowState Enumeration

Used for finding, accessing changed rows The HasChanges Method determines if

changes have been made to a dataset Returns a boolean value

The GetChanges Method is used to retrieve datatable rows that have changes Use an empty argument to retrieve all

changed rows OR specify type of changes using enumeration values

The Binding Source

Controls record position within a table

Assures that all bound controls on a form display data from the same record

Can bind controls in design time or in code

Binding Source Properties

Position property holds the current row number (zero based)

Count property indicates the number of records in a table

The Current Property returns the current row

Binding Source Methods

Binding Source Events The CurrentChanged event occurs

when a bound value is changed The PositionChanged event occurs

when a user navigates to another record

Adding an Event Handler

An event handler executes automatically when an event occurs.

Need to write event handlers for objects declared in code Write the procedure you want to execute

when the event occurs, including the sender and eventargs arguments

Add the handler in another procedure (such as constructor), which is called a delegate turns the general procedure written into an

event procedure

DataRow Versions

The DataRow object maintains several versions of its column data Current, Original, Default, Proposed

If no changes have been made, the Current and Original versions are the same

When EndEdit executes, the Current version is replaced by the Proposed

The EndEdit method confirms the changes Changes are made when the

AcceptChanges method executes

Changing Data

Changes are made to the dataset, not to the original data source.

Execute the data adapter’s Update method before calling the AcceptChanges method.

The AcceptChanges Method

Calls the EndEdit method of the data row Removes all rows marked for deletion Makes the adds and edits indicated for the table Sets the Original version of each changed row

to the Current version Sets RowState of each row to Unchanged The RejectChanges replaces Current versions

with the Original versions After AcceptChanges or RejectChanges

executes, all RowState properties are reset to Unchanged

Data Adapter Update Method Update writes the changes to the

database using SQL action queries Uses a group of Command Objects

One each for insert, update and delete Can use actual queries or refer to stored

procedures

When to Update?

Every time an add, edit, delete occurs?

When the program terminates? Provide a Save option on a menu and

prompt for unsaved changes when the program terminates?

Update Considerations

Where does the application and data reside?

How many users can make changes? Does the data source need to be up-

to-date at all times?

Concurrency

Concurrency control is the process of handling conflicts in updates by multiple users.

Pessimistic concurrency control – a row is unavailable from the time the record is retrieved until the update is complete

Optimistic concurrency control – a row is unavailable only while an update is in progress (default)

“Last in wins” – A row is unavailable only when the update is being made.

Parent/Child Relationships To maintain referential integrity,

update in the following order: Delete any child records Insert, update, and delete the parent

records Insert and update the child records

Displaying Related Data

Use a DataRelation Use GetChildRows/GetParentRow methods Use a Binding Source that uses a Datarelation as

its datasource Filter rows by

Using a For loop and adding to an array or datable

Use table.Select method Requery database for related records

Use Parameter Query; or Use a variable and build a Select statement with

where clause

Stored Procedures

Can store compiled SQL statement in database Helps reduce security threats Can reduce data passed across network

Typically work directly with a command object Need to set command type Need to establish connection for

command

Parameters

Stored procedures accept and return values through parameters Input parameters are similar to

arguments in procedural languages Command object has a parameters

collection to specify parameters to use with stored procedure

Can use parameters to pass criteria or values to edit rows