Professional ASP.NET 3.5 in C# and Visual Basic Part 54 pps

End Sub C# protected void Page_Loadobject sender, EventArgs e { MoviesDataContext dc = new MoviesDataContext; var query = from m in dc.Movies select m; System.Diagnostics.Debug.WriteLine

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End Sub

C#

protected void Page_Load(object sender, EventArgs e)

{

MoviesDataContext dc = new MoviesDataContext();

var query = from m in dc.Movies

select m;

System.Diagnostics.Debug.WriteLine(query);

this.GridView1.DataSource = query;

this.GridView1.DataBind();

}

Now, when you debug the Web site using Visual Studio, you can see the SQL query, as shown

in Figure 9-11

Figure 9-11 The SQL query generated by LINQ to SQL

As you can see, the SQL generated is standard SQL syntax, and LINQ is quite good at optimizing the

queries it generates, even for more complex queries such as the grouping query shown in Listing 9-26

Listing 9-26: Grouping LINQ to SQL data

VB

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)

Dim dc As New MoviesDataContext()

Dim query = From m In dc.Movies _

Group By m.Genre Into g = Group, Count() System.Diagnostics.Debug.WriteLine(query)

Me.GridView1.DataSource = query

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End Sub

C#

{

group m by m.Genre into g

}

The generated SQL for this query is shown in Figure 9-12

Figure 9-12 Grouping SQL data using LINQ to SQL

Note that SQL to LINQ generates SQL that is optimized for SQL Server 2005

LINQ also includes a logging option you can enable by setting the Log property of the data context

While LINQ to SQL does an excellent job generating the SQL query syntax, there may be times where it is more appropriate to use other SQL query methods, such as Stored Procedures, or Views LINQ supports using the predefined queries as well

To use a SQL View with LINQ to SQL, you simply drag the View onto the LINQ to SQL design surface just as you would a standard SQL table Views appear on the design surface, just as the tables we added earlier Once the View is on the design surface, you can execute queries against it, just as you did the SQL tables This is shown in Listing 9-27

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Listing 9-27: Querying LINQ to SQL data using a View

VB

Dim query = From m In dc.AllMovies _

Select m System.Diagnostics.Debug.WriteLine(query)

Me.GridView1.DataSource = query

Me.GridView1.DataBind()

End Sub

C#

{

var query = from m in dc.AllMovies

select m;

}

Unlike Tables or Views, which LINQ to SQL exposes as properties, Stored Procedures can require

param-eters Therefore, LINQ to SQL exposes from the data context object them as method calls, allowing you to

provide method parameter values which are translated by LINQ into store procedure parameters Listing

2-28 shows a simple stored procedure you can use to retrieve a specific Genre from the database

Listing 9-28: Simple SQL Stored procedure

CREATE PROCEDURE dbo.GetGenre

(

@id int

)

AS

SELECT * FROM Genre WHERE ID = @id

You can add a Stored Procedure to your LINQ to SQL designer just as you did the Tables and Views,

by dragging them from the Server Explorer onto the LINQ to SQL Classes design surface If you expect

your stored procedure to return a collection of data from a table in your database, you should drop

the stored procedure onto the LINQ class that represents the types returned by the query In the case

of the stored procedure shown in Listing 9-28, it will return all of the Genre records that match the

provided ID, therefore you should drop the GetGenres stored procedure onto the Genres table in the

Visual Studio designer This tells the designer to generate a method which returns a generic collection of

Genre objects Once you drop the stored procedure onto the design surface, unlike the Tables and Views,

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the Stored Procedure will be displayed in a list on the right-hand side of the design surface The GetGenre stored procedure is shown after being added in Figure 9-13

Figure 9-13 The GetGenre stored procedure has been added to the Method Pane in the LINQ to SQL

design surface

After you have added the Stored Proceedures, you can access them through the data context, just

as the Table and Views we accessed As was stated earlier, however, LINQ to SQL exposes them

as method calls Therefore, they may require you to provide method parameters, as shown in

Listing 9-29

Listing 9-29: Selecting data from a Stored Procedure

VB

Me.GridView1.DataSource = dc.GetGenre(1)

Me.GridView1.DataBind()

End Sub

Continued

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{

this.GridView1.DataSource = dc.GetGenre(1);

}

Insert, Update, and Delete Queries through LINQ

Not only can LINQ to SQL be used to create powerful queries that select data from a data source, but it

can also manage insert, updates, and delete operations By default, LINQ to SQL does this in much the

same manner as selecting data LINQ to SQL uses the object class representations of the SQL structures

and dynamically generates SQL Insert, Update, and Delete commands As with selection, you can also

use Stored Procedures to perform the insert, update, or deletes

Insert Data Using LINQ

Inserting data using LINQ to SQL is as easy as creating a new instance of the object you want to insert,

and adding that to the object collection The LINQ classes provide two methods called InsertOnSubmit

and InsertAllOnSubmit which make it simple to create and add any object to a LINQ collection The

InsertOnSubmit accepts a single entity as its method parameter, allowing you to insert a single entity,

while the InsertAllOnSubmit method accepts a collection as its method parameter, allowing you to insert

an entire collection of data in a single method call

Once you have added your objects, LINQ to SQL does require the extra step of calling the Data Context

objects SubmitChanges method Calling this method tells LINQ to initiate the Insert action Listing 9-30

shows an example of creating a new Movies object, and then Adding it to the Movies collection and

calling SubmitChanges to persist the change back to the SQL database

Listing 9-30: Inserting data using LINQ to SQL

VB

Dim m As New Movie With {.Title = "The Princess Bride", Director =

"Rob Reiner", _

.Genre = 0, ReleaseDate = DateTime.Parse("9/25/1987"), Runtime = 98}

dc.Movies.InsertOnSubmit(m)

dc.SubmitChanges()

End Sub

C#

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Movie m = new Movie { Title="The Princess Bride", Director="Rob Reiner", Genre=0,

ReleaseDate=DateTime.Parse("9/25/1987"), Runtime=98 } ; dc.Movies.InsertOnSubmit(m);

dc.SubmitChanges();

}

Using Stored Procedures to Insert Data

Of course, you may already have a complex stored procedure written to handle the insertion of data into your database table LINQ makes it simple to use an existing Stored Procedure to insert data into a table

To do this, on the LINQ to SQL design surface, select the entity you want to insert data into, which in this case is the Movies entity After selecting the entity, open its properties window and locate the Default

Methods section, as shown in Figure 9-14

Figure 9-14 The properties of the Movies Default Methods section enable you to configure the Delete,

Insert, and Update behavior of LINQ to SQL for this table

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The Default Methods section contains three properties, Delete, Insert, and Update, which define the

behavior LINQ should use when executing these actions on the Movies table By default, each property

is set to the valueUseRuntime, which tells LINQ to dynamically generate SQL statements at runtime

Because you want to insert data into the table using a Stored Procedure, open the Insert properties

Con-figure Behavior dialog

In the dialog, change the Behavior radio button selection from Use Runtime to Customize Next, select

the appropriate stored procedure from the drop-down list below the radio buttons When you select the

stored procedure, LINQ automatically tries to match the table columns to the stored procedure input

parameters However, you can change these manually, if needed

The final Configure Behavior dialog is shown in Figure 9-15

Figure 9-15 Configure Behavior dialog configured for the InsertMovie Stored Procedure

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Now, when you run the code from Listing 9-30, LINQ will use the stored procedure you configured

instead of dynamically generating a SQL Insert statement

Update Data using LINQ

Updating data with LINQ is very similar to inserting data The first set is to get the specific object you

want to update You can do this by using the Single method of the collection you want to change The

scalar Single method returns a single object from the collection based on its input parameter If more than one record matches the parameters, the Single method simply returns the first match

Once you have the record you want to update, you simply change the object’s property values, and then call the data context’s SubmitChanges method Listing 9-31 shows the code required to update a specific Movie

Listing 9-31: Updating data using LINQ to SQL

VB

Dim movie = dc.Movies.Single(Function(m) m.Title = "Fletch")

movie.Genre = 1

dc.SubmitChanges()

End Sub

C#

{

var movie = dc.Movies.Single(m => m.Title == "Fletch");

movie.Genre = 1;

dc.SubmitChanges();

}

Handling Data Concurrency

LINQ to SQL also includes and uses by default optimistic concurrency That means that if two users

retrieve the same record from the database and both try to update it, the first user to submit their update

to the server wins If the second user attempts to update the record after the first, LINQ to SQL will detect that the original record has changed and will raise a ChangeConflictException

Deleting Data Using LINQ

Finally, LINQ to SQL also enables you to delete data from your SQL data source Each data class object generated by the LINQ to SQL designer also includes two methods that enable you to delete objects

from the collection, theDeleteOnSubmitandDeleteAllOnSubmitmethods As the names imply, the

DeleteOnSubmitmethod removes a single object from the collection, whereas theDeleteAllOnSubmit

method removes all records from the collection

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Listing 9-32 shows how you can use LINQ and theDeleteOnSubmitandDeleteAllOnSubmitmethods to

delete data from your data source

Listing 9-32: Deleting data using LINQ to SQL

VB

’Select and remove all Action movies Dim query = From m In dc.Movies _

Where (m.Genre = 2) _ Select m

dc.Movies.DeleteAllOnSubmit(query)

’Select a single movie and remove it Dim movie = dc.Movies.Single(Function(m) m.Title = "Fletch") dc.Movies.DeleteOnSubmit(movie)

dc.SubmitChanges() End Sub

C#

{

//Select and remove all Action movies

where m.Genre == 2 select m;

dc.Movies.DeleteAllOnSubmit(query);

//Select a single movie and remove it

var movie = dc.Movies.Single(m => m.Title == "Fletch");

dc.Movies.DeleteOnSubmit(movie);

dc.SubmitChanges();

}

As with the other SQL commands, you must remember to call the Data ContextsSubmitChangesmethod

in order to commit the changes back to the SQL data source

Extending LINQ

This chapter focuses primarily on the LINQ capabilities included in the NET framework, but LINQ is

highly extensible and can be used to create query frameworks over just about any data source While

showing you how to implement you own LINQ provider is beyond the scope of this chapter, there are

lots of implementations of LINQ that query a wide variety of data stores such as LDAP, Sharepoint, and

evenAmazon.com

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Roger Jennings from Oakleaf Systems maintains a list of third-party LINQ providers on his blog which can be found athttp://oakleafblog.blogspot.com/2007/03/third-party-linq-providers.html

Summar y

This chapter has introduced you to the new Language Integrated Query, or LINQ, features of NET 3.5, which greatly simplifies the querying of data in NET LINQ makes query a first class concept, embedded directly in NET

In this review of LINQ, we first looked at the current methods for performing object queries, including

basic data filtering, grouping, and sorting We looked at the shortcomings of current object query

tech-niques, including the requirement for developers to not only define what the query should do, but also exactly how it should do it Additionally, we looked at how even simple operations can result in highly complex code that can be difficult to read and maintain

Next, we began looking at the three basic types of LINQ — LINQ to Objects, LINQ to XML, and LINQ

to SQL Each flavor of LINQ uses the same basic query syntax to dramatically simplify the querying

of Objects, XML or SQL We looked at how you can use the basic SQL-like query syntax for selection,

filtering, and grouping This query syntax is clean and easily readable, and also includes many of the

same operator features as SQL

We also looked at the basic O/R mapper that is included with LINQ to SQL The O/R mapper makes it easy to create CLR objects that represent SQL structures such as Tables, Views, and Stored Procedures

Once the CLR objects are created, LINQ can be used to query the objects

Finally we looked at how using LINQ to SQL, you can easily change the data in your database, using

generated SQL statements, or using custom Stored Procedures

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