2009 Pearson Education, Inc. All rights reserved. 1 21 Databases and LINQ to SQL.

2009 Pearson Education, Inc. All rights reserved.

1

2121

Databases andLINQ to SQL


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It is a capital mistake to theorizebefore one has data.

– Arthur Conan Doyle

Now go, write it before them in a table,and note it in a book, that it may be forthe time to come for ever and ever.

– Isaiah 30:8


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Get your facts first, and then youcan distort them as much as you please.

– Mark Twain

I like two kinds of men:domestic and foreign.

– Mae West


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OBJECTIVES

In this chapter you will learn: The relational database model. To write basic database queries in SQL. To use LINQ to SQL to retrieve and manipulate data

from a database. To add data sources to projects. To use the Object Relational Designer to create LINQ

to SQL classes. To use the IDE’s drag-and-drop capabilities to display

database tables in applications. To use data binding to move data seamlessly between

GUI controls and databases. To create Master/Detail views.


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21.1 Introduction

21.2 Relational Databases

21.3 Relational Database Overview: Books Database

21.4 SQL

21.5 LINQ to SQL

21.6 LINQ to SQL: Extracting Information from a Database

21.7 More Complex LINQ Queries and Data Binding

21.8 Retrieving Data from Multiple Tables with LINQ

21.9 Creating a Master/Detail View Application

21.10 Programming with LINQ to SQL: Address-Book Case Study


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21.1 Introduction

• A database is an organized collection of data.

• A database management system (DBMS) organizes data for many users.

• Relational databases organize data as tables with rows and columns.

• Structured Query Language (SQL) is the international standard language used with relational databases.


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Figure 21.1 illustrates a sample Employees table.

• The ID column is the table’s primary key—a column used to uniquely identify a row.

• A primary key composed of two or more columns is a composite key.

Fig. 21.1 | Employees table sample data.

21.2 Relational Databases


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• Each column represents a different data attribute.

• Most users of a database use only subsets of the rowsand columns.

• Programs use SQL to define queries that select subsetsof the data from a table (Fig. 21.2).

Fig. 21.2 | Distinct Department and Location data fromthe Employees table.

21.2 Relational Databases (Cont.)


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Column Description

AuthorID Author’s ID number in the database (primary key).

FirstName Author’s first name (a string).

LastName Author’s last name (a string).

Fig. 21.3 | Authors table of the Books database.

• A database’s tables, their fields and the relationships between them are collectively known as a database schema.

• The Authors table has three fields, represented by columns (Fig. 21.3).

21.3 Relational Database Overview: Books Database


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AuthorID FirstName LastName

1 Harvey Deitel

2 Paul Deitel

3 Greg Ayer

4 Dan Quirk

Fig. 21.4 | Data from the Authors table of the Books database.

• Figure 21.4 contains the data from the Authors table.

21.3 Relational Database Overview: Books Database (Cont.)


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Column Description

ISBN ISBN of the book (a string). The table’s primary key.

BookTitle Title of the book (a string).

EditionNumber Edition number of the book (an integer).

Copyright Copyright year of the book (a string).


Fig. 21.5 | Titles table of the Books database.

• The Titles table (described in Fig. 21.5) consists of four columns.


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ISBN BookTitle Edition-Number

Copy-right

0131752421 Internet & World Wide Web How to Program 4 2008

0132222205 Java How to Program 7 2007

0132404168 C How to Program 5 2007

0136053033 Simply Visual Basic 2008 3 2009

013605305X Visual Basic 2008 How to Program 4 2009

013605322X Visual C# 2008 How to Program 3 2009

0136151574 Visual C++ 2008 How to Program 2 2008

0136152503 C++ How to Program 6 2008


Fig. 21.6 | Data from the Titles table of the Books database.

• Figure 21.6 contains the data from the Titles table.


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Column Description

AuthorID The author’s ID number, a foreign key to the Authors table.

ISBN The ISBN for a book, a foreign key to the Titles table.

Fig. 21.7 | AuthorISBN table of the Books database.

• The AuthorISBN table (described in Fig. 21.7) matches the AuthorID and ISBN columns.

• These foreign keys form a composite primary key.



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AuthorID ISBN AuthorID ISBN

1 0131752421 2 0132222205

1 0132222205 2 0132404168

1 0132404168 2 0136053033

1 0136053033 2 013605305X

1 013605305X 2 013605322X

1 013605322X 2 0136151574

1 0136151574 2 0136152503

1 0136152503 3 0136053033

2 0131752421 4 0136151574

Fig. 21.8 | Data from the AuthorISBN table of Books.

• Figure 21.8 contains the data from the Author ISBN table of the Books database.



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• Rule of Referential Integrity: every foreign-key value must be another table’s primary-key value.

• Foreign keys also allow related data in multiple tables to be joined.

• A foreign key can appear many times in a table but only once (as the primary key) in its original table.



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Common Programming Error 21.2

Providing the same value for the primary key in multiple rows breaks the Rule of Entity Integrity and causes the DBMS to report an error.


Providing a foreign-key value that does not appear as a primary-key value in another table breaks the Rule of Referential Integrity and causes the DBMS to report an error.


Not providing a value for every column in a primary key breaks the Rule of Entity Integrity and causes the DBMS to report an error.



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• Figure 21.9 is an entity-relationship (ER) diagram forthe Books database.

• Note that primary keys are italic.

• On the Authors end of the line, there is a 1, and on the AuthorISBN end, an infinity symbol (∞), indicating aone-to-many relationship.

Fig. 21.9 | Entity-relationship diagram for the Books database.



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SQL keyword Description

SELECT Retrieves data from one or more tables.

FROM Specifies the tables involved in a query. Required in every query.

WHERE Specifies optional criteria for selecting rows.

ORDER BY Specifies optional criteria for ordering rows.

INNER JOIN Specifies optional operator for merging rows from multiple tables.

INSERT Inserts rows in a specified table.

UPDATE Updates rows in a specified table.

DELETE Deletes rows from a specified table.

Fig. 21.10 | Common SQL keywords.

• Figure 21.10 lists some common SQL keywords.

21.4 SQL


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21.4.1 Basic SELECT Query• A SQL query “selects” rows and columns from one or

more tables in a database.SELECT * FROM tableName

• The asterisk (*) indicates that all the columns from the tableName table should be retrieved.

• To retrieve all the data in the Authors table:

SELECT * FROM Authors

21.4 SQL (Cont.)


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AuthorID LastName

1 Deitel

2 Deitel

3 Ayer

4 Quirk

Fig. 21.11 | AuthorID and LastName data from the Authors table.

• To retrieve only specific columns, use a list of the column names:

SELECT AuthorID, LastName FROM Authors

• This query returns the data listed in Fig. 21.11.

21.4 SQL (Cont.)


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21.4.2 WHERE Clause • Users can query a database for rows that satisfy certain

selection criteria.

• The basic form of a query with selection criteria isSELECT columnName1, columnName2, FROM tableName WHERE criteria

21.4 SQL (Cont.)


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BookTitle EditionNumber Copyright

Internet & World Wide Web How to Program 4 2008

Simply Visual Basic 2008 3 2009

Visual Basic 2008 How to Program 4 2009

Visual C# 2008 How to Program 3 2009

Visual C++ 2008 How to Program 2 2008

C++ How to Program 6 2008

Fig. 21.12 | Books with copyright dates after 2007 from table Titles.

• To select books for which the Copyright is more recent than 2007:

SELECT BookTitle, EditionNumber, Copyright.

FROM Titles

WHERE Copyright > '2007'• Figure 21.12 shows the result of the preceding query.

21.4 SQL (Cont.)


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• Operator LIKE is used for pattern matching.

• A pattern with a percent character (%) searches for zero or more characters at the percent character’s position.

• The following query locates authors whose last names start with the letter D:

SELECT AuthorID, FirstName, LastNameFROM AuthorsWHERE LastName LIKE 'D%'

21.4 SQL (Cont.)


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1 Harvey Deitel

2 Paul Deitel

Fig. 21.13 | Authors from the Authors table whose last names start with D.

• The preceding query selects the two rows shown in Fig. 21.13.

21.4 SQL (Cont.)


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• An underscore (_) indicates a single wildcard character at that position.

• The following query locates authors whose last names have the letter y as the second letter.

SELECT AuthorID, FirstName, LastNameFROM AuthorsWHERE LastName LIKE '_y%'

21.4 SQL (Cont.)


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3 Greg Ayer

Fig. 21.14 | The only author from the Authors table whose last name contains y as the second letter.

• The preceding query produces the row shown in Fig. 21.14.

21.4 SQL (Cont.)


27

21.4.3 ORDER BY Clause• Rows in the result can be sorted into ascending or

descending order by using the optional ORDER BY clause.SELECT columnName1, columnName2, FROM

tableName ORDER BY column ASC

SELECT columnName1, columnName2, FROM

tableName ORDER BY column DESC

• ASC specifies ascending order, DESC specifies descending order

• column specifies the column on which the sort is based.

21.4 SQL (Cont.)


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3 Greg Ayer

1 Harvey Deitel

2 Paul Deitel

4 Dan Quirk

Fig. 21.15 | Authors from table Authors in ascending order by LastName.

• To obtain the list of authors in ascending order by last name (Fig. 21.15), use the query

SELECT AuthorID, FirstName, LastName

FROM Authors

ORDER BY LastName ASC

21.4 SQL (Cont.)


29


4 Dan Quirk

1 Harvey Deitel

2 Paul Deitel

3 Greg Ayer

Fig. 21.16 | Authors from table Authors in descending order by LastName.

• To obtain the same list of authors in descending order by last name (Fig. 21.16), use

SELECT AuthorID, FirstName, LastName

FROM Authors

ORDER BY LastName DESC

21.4 SQL (Cont.)


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• Multiple columns can be used for sorting with an ORDER BY clause:

ORDER BY column1 sortingOrder, column2 sortingOrder,…

• Note that the sortingOrder does not have to be identical for each column.

21.4 SQL (Cont.)


31

SELECT BookTitle, EditionNumber,Copyright

FROM Titles

ORDER BY Copyright DESC, BookTitle ASC• This query returns books sorted first in descending

order by copyright date, then in ascending order by title (Fig. 21.17).

21.4 SQL (Cont.)


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BookTitle EditionNumber Copyright

Simply Visual Basic 2008 3 2009

Visual Basic 2008 How to Program 4 2009

Visual C# 2008 How to Program 3 2009

C++ How to Program 6 2008

Internet & World Wide Web How to Program 4 2008

Visual C++ 2008 How to Program 2 2008

C How to Program 5 2007

Java How to Program 7 2007

Fig. 21.17 | Data from Titles in descending order by Copyright and ascending order by BookTitle.

21.4 SQL (Cont.)


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• The WHERE and ORDER BY clauses can be combined.

• ORDER BY must be the last clause in the query.SELECT ISBN, BookTitle,

EditionNumber, Copyright

FROM Titles

WHERE BookTitle LIKE '%How to Program'

ORDER BY BookTitle ASC

21.4 SQL (Cont.)


34

• The query results are shown in Fig. 21.18.

ISBN BookTitle EditionNumber Copyright

0132404168 C How to Program 5 2007

0136152503 C++ How to Program 6 2008

0131752421 Internet & World Wide Web How to Program 4 2008

0132222205 Java How to Program 7 2007

013605305X Visual Basic 2008 How to Program 4 2009

013605322X Visual C# 2008 How to Program 3 2009

0136151574 Visual C++ 2008 How to Program 2 2008

Fig. 21.18 | Books from table Titles whose BookTitles end with How to Program in ascending order by BookTitle.

21.4 SQL (Cont.)


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21.4.4 Retrieving Data from Multiple Tables:

INNER JOIN• Database designers typically normalize databases—i.e.,

split related data into separate tables to ensure that a database does not store redundant data.

• For example, we use a table to store “links” between authors and titles.

• If we did not separate this information into individual tables, we would need to include author information with each entry in the Titles table.

21.4 SQL (Cont.)


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• Often, it is desirable to merge data from multiple tables into a single result.

• An INNER JOIN merges rows from two tables by testing for matching values in a column that is common to the tables:

SELECT columnName1, columnName2,…

FROM table1 INNER JOIN table2

ON table1.columnName = table2.columnName

21.4 SQL (Cont.)


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• The ON clause specifies the columns from each table that are compared to determine which rows are merged.

• The following query produces a list of authors accompanied by the ISBNs for books written by each author:

SELECT FirstName, LastName, ISBN

FROM Authors INNER JOIN AuthorISBN

ON Authors.AuthorID = AuthorISBN.AuthorID

ORDER BY LastName, FirstName

Common Programming Error 21.4In a SQL query, failure to qualify names for columnsthat have the same name in two or more tables is an error.

21.4 SQL (Cont.)


38

• Figure 21.19 depicts the results of the preceding query, ordered by LastName and FirstName.

Fig. 21.19 | Authors and ISBNs for their books in ascending order by LastName and FirstName. (Part 1 of 2.)

FirstName LastName ISBN

Greg Ayer 0136053033

Harvey Deitel 0131752421




Harvey Deitel 013605305X

21.4 SQL (Cont.)


39

FirstName LastName ISBN




Paul Deitel 0131752421




Paul Deitel 013605305X

Paul Deitel 013605322X



Dan Quirk 0136151574

Fig. 21.19 | Authors and ISBNs for their books in ascending order by LastName and FirstName. (Part 2 of 2)

21.4 SQL (Cont.)


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21.4.5 INSERT Statement • The INSERT statement inserts a row into a table:INSERT INTO tableName ( columnName1, columnName2,…,

columnNameN )

VALUES ( value1, value2, … , valueN )

• The SQL keyword VALUES specifies values in the new row.

• The values must match up with the columns specified after the table name in both order and type.

21.4 SQL (Cont.)


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• The following INSERT statement inserts a row into the Authors table:

INSERT INTO Authors ( FirstName, LastName )

VALUES ( 'Sue', 'Smith' )

• AuthorID is an identity column, so it is assigned the next value in an autoincremented sequence.

21.4 SQL (Cont.)


42

• Figure 21.20 shows the Authors table after the INSERT operation.

Fig. 21.20 | Table Authors after an INSERT operation.


1 Harvey Deitel

2 Paul Deitel

3 Greg Ayer

4 Dan Quirk

5 Sue Smith

21.4 SQL (Cont.)


43

Common Programming Error 21.5It is an error to specify a value for an identity columnin an INSERT statement.

Common Programming Error 21.6To specify a string containing a single quote in a SQL statement, there must be two single quotes in the position where the single-quote character appears in the string(e.g., 'O''Malley').

21.4 SQL (Cont.)


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21.4.6 UPDATE Statement

An UPDATE statement modifies data in a table:UPDATE tableName

SET columnName1 = value1, columnName2 = value2, … , columnNameN =valueN

WHERE criteria

• The following UPDATE statement updates a row in the Authors table.

UPDATE Authors

SET LastName = 'Jones‘

WHERE LastName = 'Smith' AND FirstName = 'Sue'

21.4 SQL (Cont.)


45

Fig. 21.21 | Table Authors after an UPDATE operation.


1 Harvey Deitel

2 Paul Deitel

3 Greg Ayer

4 Dan Quirk

5 Sue Jones

• Figure 21.21 shows the Authors table after the UPDATE operation has taken place.

21.4 SQL (Cont.)


46

• Keyword AND is a logical operator that returns true if and only if both of its operands are true.

• SQL also provides other logical operators, such as OR and NOT.

21.4 SQL (Cont.)


47

21.4.7 DELETE Statement

• A DELETE statement removes rows from a table:DELETE FROM tableName WHERE criteria

• The following DELETE statement deletes the rowfor Sue Jones.

DELETE FROM Authors WHERE LastName = 'Jones' AND FirstName = 'Sue'

21.4 SQL (Cont.)


48

Fig. 21.22 | Table Authors after a DELETE operation.


1 Harvey Deitel

2 Paul Deitel

3 Greg Ayer

4 Dan Quirk

• Figure 21.22 shows the Authors table after the DELETE operation has taken place.

21.4 SQL (Cont.)


49

• LINQ to SQL uses LINQ syntax to query databases.

• LINQ to SQL classes are automatically generated by the IDE’s LINQ to SQL Designer.

• The IDE creates a class for each table, with a property for each column in the table.

21.5 LINQ to SQL


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• A cache is a temporary store created for fast access to data.

• LINQ to SQL caches all row objects that it creates, making interacting with the database more efficient.

• This can reduce round trips to the database.

21.5 LINQ to SQL (Cont.)


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• LINQ queries on an IQueryable object are processed together as a single SQL statement.

• If each query operator were handled separately, multiple round trips to the database would be needed.

• A DataContext class controls the flow of data between the program and the database.

• When cached objects have been changed, these changes are saved using the DataContext’s SubmitChanges method.

21.5 LINQ to SQL (Cont.)


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21.6 LINQ to SQL: Extracting Information from a Database

21.6.1 Creating LINQ to SQL Classes• Create a new Windows Forms Application named DisplayTable.

• Change the name of the source file to DisplayTableForm.cs.


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21.6 LINQ to SQL: Extracting Information from a Database (Cont.)

• Select Tools > Connect to Database….

• If the Choose Data Source dialog appears, select Microsoft SQL Server Database File from the Data source: ListBox.

• Click Continue to open the Add Connection dialog.

• Click Browse… and choose Books.mdf.

Error-Prevention Tip 21.1

SQL Server Express allows only one application at a time to access a database file. Ensure that no other program is using the database file before you attempt to add it to the project.


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• Right click the project in the Solution Explorer and select Add > New Item…

• Select LINQ to SQL classes, name the new item Books.dbml and click the Add button.

• The Database Explorer window allows you navigate the structure of databases.

• Drag the Authors, Titles and AuthorISBN tables onto the Object Relational Designer and select Yes.

Error-Prevention Tip 21.2

Be sure to save the file in the Object Relational Designer before trying to use the LINQ to SQL classes in code. The IDE does not generate the classes until you save the file.


55


21.6.2 Creating Data Bindings• Select Data > Add New Data Source…

to display the Data Source Configuration Wizard.

• In the dialog, select Object and click Next >.

• Expand the tree view and select DisplayTable > DisplayTable > Author.

• Click Next > then Finish. The Authors table inthe database is now a data source that can be used bythe bindings.


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• Open the Data Sources window by selecting Data > Show Data Sources.

• Open the DisplayTableForm in Design view.

• Click the Author node in the Data Sources window—it should change to a drop-down list. Ensure that the DataGridView option is selected.


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• Drag the Author node from the Data Sources window to the DisplayTableForm.

• The IDE creates a DataGridView with the correct column names and a BindingNavigator.


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• The BindingNavigator contains Buttons for moving between entries, adding entries, deleting entries and saving changes to the database.

• A BindingSource transfers data between the data source and the data-bound controls on the Form. (Fig. 21.23).


59


Fig. 21.23 | Component tray holds nonvisual components in Design view.

Component tray


60

Outline

DisplayTableForm.cs

( 1 of 3 )

1 // Fig. 21.24: DisplayTableForm.cs

2 // Displaying data from a database table in a DataGridView.

3 using System;

4 using System.Linq;

5 using System.Windows.Forms;

6

7 namespace DisplayTable

8 {

9 public partial class DisplayTableForm : Form

10 {

11 // constructor

12 public DisplayTableForm()

13 {

14 InitializeComponent();

15 } // end constructor

16

• Figure 21.24 shows the code needed to move data back and forth between the database and GUI.

Fig. 21.24 | Component tray holds nonvisual components inDesign view. (Part 1 of 3. )


61

17 // LINQ to SQL data context

18 private BooksDataContext database = new BooksDataContext();

19

20 // load data from database into DataGridView

21 private void DisplayTableForm_Load( object sender, EventArgs e )

22 {

23 // use LINQ to order the data for display

24 authorBindingSource.DataSource =

25 from author in database.Authors

26 orderby author.AuthorID

27 select author;

28 } // end method DisplayTableForm_Load

29

30 // click event handler for the Save Button in the

31 // BindingNavigator saves the changes made to the data

32 private void authorBindingNavigatorSaveItem_Click(

Outline

DisplayTableForm.cs

( 2 of 3 )

A DataContext object allows the application to interact with the database.

The BindingSource’s DataSource property is set to the results of a LINQ query.

LINQ is used to extract data from the Authors table in the database.



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33 object sender, EventArgs e )

34 {

35 Validate(); // validate input fields

36 authorBindingSource.EndEdit(); // indicate edits are complete

37 database.SubmitChanges(); // write changes to database file

38 } // end method authorBindingNavigatorSaveItem_Click

39 } // end class DisplayTableForm

40 } // end namespace DisplayTable

Outline

DisplayTableForm.cs

( 3 of 3 )

First, all controls on the form are validated.

EndEdit forces any pending changes to be saved.

SubmitChanges stores any changes to the database.



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• Use the Properties window to set the save button’s Enabled property to True.

• Saving the data back to the database is a three-step process:

– First, all controls on the form are validated.

– EndEdit forces any pending changes to be saved.

– SubmitChanges stores any changes to the database.


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• To persist changes between program executions, select the database in the Solution Explorer and set the Copy to Output Directory property to Copy if newer.

• Run the application to verify that it works.


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21.7 More Complex LINQ Queries and Data Binding

• Create a new Windows Forms Application named DisplayQueryResult.

• Rename its C# file to DisplayQueryResultForm.cs.

• Add the Books database to the project and generate the LINQ to SQL classes.


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21.7 More Complex LINQ Queries and Data Binding (Cont.)

• Create the data source and the DataGridView.

• Select the Title class as the data source, and drag the Title node from the Data Sources window onto the form.

• Leave the Form’s Design view open and add a ComboBox named queriesComboBox below the DataGridView on the Form.

• Open the String Collection Editor by clicking the small arrowhead that appears in the upper-right corner of the control and selecting Edit Items.


67


• Add the following three items to queriesComboBox:

– All titles

– Titles with 2008 copyright

– Titles ending with "How to Program"


68

1 // Fig. 21.25: DisplayQueryResultForm.cs

2 // Displaying the result of a user-selected query in a DataGridView.

3 using System;



6

7 namespace DisplayQueryResult

8 {

9 public partial class DisplayQueryResultForm : Form

10 {

11 // constructor

12 public DisplayQueryResultForm()

13 {



16



19

Outline

DisplayQueryResultForm.cs

( 1 of 5)

• The application executes the appropriate query when the user selects an item (Fig. 21.25).

Fig. 21.25 | Displaying the result of a user-selected query in a DataGridView. (Part 1 of 5. )

Declaring the BooksDataContext.


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20 // load data from database into DataGridView

21 private void DisplayQueryResultForm_Load(


23 {

24 // write SQL to standard output stream

25 database.Log = Console.Out;

26

27 // set the ComboBox to show the default query that

28 // selects all books from the Titles table

29 queriesComboBox.SelectedIndex = 0;

30 } // end method DisplayQueryResultForm_Load

31

32 // Click event handler for the Save Button in the


34 private void titleBindingNavigatorSaveItem_Click(


36 {

37 Validate(); // validate input fields

38 titleBindingSource.EndEdit(); // indicate edits are complete


40

Outline


( 2 of 5)


Enable the save Button so this event handler will execute.

Setting the BooksDataContext’s Log property, where all commands will be recorded.


70

41 // when saving, return to "all titles" query

42 queriesComboBox.SelectedIndex = 0;

43 } // end method titleBindingNavigatorSaveItem_Click

44

45 // loads data into TitleBindingSource based on user-selected query

46 private void queriesComboBox_SelectedIndexChanged(


48 {

49 // set the data displayed according to what is selected

50 switch ( queriesComboBox.SelectedIndex )

51 {

52 case 0: // all titles

53 // use LINQ to order the books by title

54 titleBindingSource.DataSource =

55 from title in database.Titles

56 orderby title.BookTitle

57 select title;

58 break;

59 case 1: // titles with 2008 copyright

60 // use LINQ to get titles with 2008

Outline


( 3 of 5)


Enable the save Button so this event handler will execute.


71

61 // copyright and sort them by title



64 where title.Copyright == "2008"


66 select title;

67 break; 68 case 2: // titles ending with "How to Program" 69 // use LINQ to get titles ending with

70 // "How to Program" and sort them by title



73 where title.BookTitle.EndsWith( "How to Program" )


75 select title;

76 break;

77 } // end switch

78

79 titleBindingSource.MoveFirst(); // move to first entry

80 } // end method queriesComboBox_SelectedIndexChanged

81 } // end class DisplayQueryResultForm

82 } // end namespace DisplayQueryResult

Outline


( 4 of 5)


The MoveFirst method focuses the first element each time a query executes.


72

Outline


( 5 of 5)



73


• The DataContext object is set to log all queries to Console.Out.

• The Output window can be opened by selecting View > Output in the IDE (Fig. 21.26).

a) SQL generated by the All titles query.

Fig. 21.26 | Output window of the Display Query Resultapplication. (Part 1 of 2. )


74


c) SQL generated by the Titles ending with "How to Program" query.

b) SQL generated by the Titles with 2008 copyright query.

Fig. 21.26 | Output window of the Display Query Resultapplication. (Part 2 of 2. )


75

1 // Fig. 21.27: JoiningTest.cs

2 // Using LINQ to perform a join and aggregate data across tables.

3 using System;


5

6 namespace JoiningWithLINQ

7 {

8 public class JoiningTest

9 {

10 public static void Main( string[] args )

11 {

12 // create database connection

13 BooksDataContext database = new BooksDataContext();

14

Outline

JoiningTest.cs

( 1 of 7 )

• Figure 21.27 uses LINQ to SQL to combine and organize data from multiple tables.

Fig. 21.27 | Using LINQ to perform a join and aggregatedata across tables. (Part 1 of 7. )


76

15 // get authors and ISBNs of each book they co-authored

16 var authorsAndISBNs =


18 join book in database.AuthorISBNs

19 on author.AuthorID equals book.AuthorID

20 orderby author.LastName, author.FirstName

21 select new { author.FirstName, author.LastName, book.ISBN };

22

23 Console.WriteLine( "Authors and ISBNs:" ); // display header

24

25 // display authors and ISBNs in tabular format

26 foreach ( var element in authorsAndISBNs )

27 {

28 Console.WriteLine( "\t{0,-10} {1,-10} {2,-10}",

29 element.FirstName, element.LastName, element.ISBN );

30 } // end foreach

31

32 // get authors and titles of each book they co-authored

33 var authorsAndTitles =


35 from book in title.AuthorISBNs

36 let author = book.Author

37 orderby author.LastName, author.FirstName, title.BookTitle

Outline

JoiningTest.cs

( 2 of 7 )

Using LINQ’s join clause to combine data from multiple tables.

Using LINQ to SQL properties to access related rows in other tables.



77

38 select new { author.FirstName, author.LastName,

39 title.BookTitle };

40

41 Console.WriteLine( "\nAuthors and titles:" ); // header 42 43 // display authors and titles in tabular format

44 foreach ( var element in authorsAndTitles )

45 {

46 Console.WriteLine( "\t{0,-10} {1,-10} {2}",

47 element.FirstName, element.LastName, element.BookTitle );

48 } // end foreach

49

50 // get authors and titles of each book

51 // they co-authored; group by author

52 var titlesByAuthor =



55 let name = author.FirstName + " " + author.LastName

56 let titles =

57 from book in author.AuthorISBNs

58 orderby book.Title.BookTitle

59 select book.Title.BookTitle

60 select new { Name = name, Titles = titles };

Outline

JoiningTest.cs

( 3 of 7 )

Using LINQ to return hierarchical results through a nested query in the second let clause.


Using LINQ to SQL properties to access related rows in other tables.


78

61

62 Console.WriteLine( "\nTitles grouped by author:" ); // header

63

64 // display titles written by each author, grouped by author

65 foreach ( var author in titlesByAuthor )

66 {

67 // display author's name

68 Console.WriteLine( "\t" + author.Name + ":" );

69

70 // display titles written by that author

71 foreach ( var title in author.Titles )

72 {

73 Console.WriteLine( "\t\t" + title );

74 } // end inner foreach

75 } // end outer foreach

76 } // end Main

77 } // end class JoiningTest

78 } // end namespace JoiningWithLINQ

Outline

JoiningTest.cs

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79

Authors and ISBNs:

Greg Ayer 0136053033












Paul Deitel 0136053033 Paul Deitel 013605305X Paul Deitel 013605322X Paul Deitel 0136151574 Paul Deitel 0136152503

Dan Quirk 0136151574

(continued on next page...)

Outline

JoiningTest.cs

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80

(continued from previous page…) Authors and titles: Greg Ayer Simply Visual Basic 2008 Harvey Deitel C How to Program Harvey Deitel C++ How to Program Harvey Deitel Internet & World Wide Web How to Program Harvey Deitel Java How to Program Harvey Deitel Simply Visual Basic 2008 Harvey Deitel Visual Basic 2008 How to Program Harvey Deitel Visual C# 2008 How to Program Harvey Deitel Visual C++ 2008 How to Program Paul Deitel C How to Program Paul Deitel C++ How to Program Paul Deitel Internet & World Wide Web How to Program Paul Deitel Java How to Program Paul Deitel Simply Visual Basic 2008 Paul Deitel Visual Basic 2008 How to Program Paul Deitel Visual C# 2008 How to Program Paul Deitel Visual C++ 2008 How to Program Dan Quirk Visual C++ 2008 How to Program (continued on next page...)

Outline

JoiningTest.cs

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81

(continued from previous page…) Titles grouped by author: Greg Ayer: Simply Visual Basic 2008 Harvey Deitel: C How to Program C++ How to Program Internet & World Wide Web How to Program Java How to Program Simply Visual Basic 2008 Visual Basic 2008 How to Program Visual C# 2008 How to Program Visual C++ 2008 How to Program Paul Deitel: C How to Program C++ How to Program Internet & World Wide Web How to Program Java How to Program Simply Visual Basic 2008 Visual Basic 2008 How to Program Visual C# 2008 How to Program Visual C++ 2008 How to Program Dan Quirk: Visual C++ 2008 How to Program

Outline

JoiningTest.cs

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82

1 // Fig. 21.28: MasterDetailForm.cs

2 // Using a DataGridView to display details based on a selection.

3 using System;



6

7 namespace MasterDetail

8 {

9 public partial class MasterDetailForm : Form

10 {

11 public MasterDetailForm()

12 {



15

16 // connection to database


18

19 // this class helps us display each author's first

20 // and last name in the authors drop-down list

Outline

MasterDetailForm.cs

( 1 of 6 )

• Figure 21.28 demonstrates a master/detail view—one part of the interface allows you to select an entry, and another part displays detailed information about that entry.

Fig. 21.28 | Using a DataGridView to display details based on a selection. (Part 1 of 6.)


83

21 private class AuthorBinding

22 {

23 public Author Author { get; set; } // contained Author object

24 public string Name { get; set; } // author's full name

25 } // end class AuthorBinding

26

27 // initialize data sources when the Form is loaded

28 private void MasterDetailForm_Load( object sender, EventArgs e )

29 {

30 // display AuthorBinding.Name

31 authorComboBox.DisplayMember = "Name";

32

33 // set authorComboBox's DataSource to the list of authors

34 authorComboBox.DataSource =



37 let name = author.FirstName + " " + author.LastName

38 select new AuthorBinding { Author = author, Name = name };

39

40 // display Title.BookTitle

41 titleComboBox.DisplayMember = "BookTitle";

Outline

MasterDetailForm.cs

( 2 of 6 )


The ComboBox’s DisplayMember property is set to "Name".

Creating an AuthorBinding object for each author as the ComboBox’s DataSource.

The text in the ComboBox is retrieved from the BookTitle property.


84

42

43 // set titleComboBox's DataSource to the list of titles

44 titleComboBox.DataSource =



47 select title;

48

49 // initially, display no "detail" data

50 booksBindingSource.DataSource = null;

51

52 // set the DataSource of the DataGridView to the BindingSource

53 booksDataGridView.DataSource = booksBindingSource;

54 } // end method MasterDetailForm_Load

55

56 // display titles that were co-authored by the selected author

57 private void authorComboBox_SelectedIndexChanged(


59 {

60 // get the selected Author object from the ComboBox

61 Author currentAuthor =

62 ( ( AuthorBinding ) authorComboBox.SelectedItem ).Author;

63

Outline

MasterDetailForm.cs

( 3 of 6 )


Creating the DataSource for titleComboBox.

Retrieving the selected Author and using LINQ to retrieve related Titles.


85

64 // set booksBindingSource's DataSource to the

65 // list of titles written by the selected author

66 booksBindingSource.DataSource =

67 from book in currentAuthor.AuthorISBNs

68 select book.Title;

69 } // end method authorComboBox_SelectedIndexChanged

70

71 // display the authors of the selected title

72 private void titleComboBox_SelectedIndexChanged(


74 {

75 // get the selected Title object from the ComboBox

76 Title currentTitle = ( Title ) titleComboBox.SelectedItem;

77

78 // set booksBindingSource's DataSource to the

79 // list of authors for the selected title

80 booksBindingSource.DataSource =

81 from book in currentTitle.AuthorISBNs

82 select book.Author;

83 } // end method titleComboBox_SelectedIndexChanged

84 } // end class MasterDetailForm

85 } // end namespace MasterDetail

Outline

MasterDetailForm.cs

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Retrieving the selected Author and using LINQ to retrieve related Titles.


86

Outline

a) Master/Detail application when it begins execution MasterDetailForm.cs

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87

Outlineb) Select Paul

Deitel from the Author: drop-down list to view books

he has co-authored

c) Select Simply

Visual Basic 2008 from the Title:

drop-down to view the authors who wrote that book

MasterDetailForm.cs

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88

21.9 Creating a Master/Detail View Application

• Create a new Windows Forms Application called MasterDetail.

• Add the Books database and create the LINQ to SQL classes.


89

21.9 Creating a Master/Detail View Application (Cont.)

• Add two Labels and two ComboBoxes, positioned as shown in Fig. 21.29.

• Create a DataGridView called booksDataGridView and set its ReadOnly property to True using the Properties window.

Fig. 21.29 | Finished design of MasterDetail application.


90

1 // Fig. 21.30: AddressBookForm.cs

2 // Manipulating an address book.

3 using System;



6

7 namespace AddressBook

8 {

9 public partial class AddressBookForm : Form

10 {

11 public AddressBookForm()

12 {



15

Outline

AddressBookForm.cs

( 1 of 5 )

• The AddressBook application (Fig. 21.30) provides a GUI for querying the database with LINQ.

Fig. 21.30 | Manipulating an address book. (Part 1 of 5.)


91


17 private AddressBookDataContext database =

18 new AddressBookDataContext();

19

20 // fill our addressBindingSource with all rows, ordered by name

21 private void BindDefault()

22 {

23 // use LINQ to create a data source from the database

24 addressBindingSource.DataSource =

25 from address in database.Addresses

26 orderby address.LastName, address.FirstName

27 select address;

28

29 addressBindingSource.MoveFirst(); // go to the first result

30 findTextBox.Clear(); // clear the Find TextBox

31 } // end method BindDefault

32

33 private void AddressBookForm_Load( object sender, EventArgs e )

34 {

Outline

AddressBookForm.cs

( 2 of 5 )


The BindDefault method sets the AddressBindingSource’s DataSource property to the result of a LINQ query.


92

35 BindDefault(); // fill binding with data from database

36 } // end method AddressBookForm_Load

37

38 // Click event handler for the Save Button in the


40 private void addressBindingNavigatorSaveItem_Click(


42 { 43 Validate(); // validate input fields 44 addressBindingSource.EndEdit(); // indicate edits are complete


46

47 BindDefault(); // change back to initial unfiltered data on save

48 } // end method addressBindingNavigatorSaveItem_Click

49

50 // load LINQ to create a data source that contains

51 // only people with the specified last name

52 private void findButton_Click( object sender, EventArgs e )

Outline

AddressBookForm.cs

( 3 of 5 )


Data is set to be displayed when the application starts.

Event handler for the BindingNavigator’s save Button.


93

53 {

54 // use LINQ to create a data source that contains

55 // only people with the specified last name

56 addressBindingSource.DataSource =

57 from address in database.Addresses

58 where address.LastName == findTextBox.Text

59 orderby address.LastName, address.FirstName

60 select address;

61

62 addressBindingSource.MoveFirst(); // go to first result

63 } // end method findButton_Click

64

65 private void browseButton_Click( object sender, EventArgs e )

66 {

67 BindDefault(); // change back to initial unfiltered data

68 } // end method browseButton_Click

69 } // end class AddressBookForm

70 } // end namespace AddressBook

Outline

AddressBookForm.cs

( 4 of 5 )


Doing a search changes the DataSource to a set of matches.


94

Outline

AddressBookForm.cs

( 5 of 5 )


a) AddressBook application after adding four entries.b) Searching for a specific last name.

c) Use the Browse All Entries Button to view all people in the address book.


95

21.10 Programming with LINQ to SQL: Address-Book Case Study

• Create a new Windows Forms Application named AddressBook.

• Add the AddressBook.mdf database and name the file AddressBook.dbml.

• You must also add the Addresses table as a data source.


96

21.10 Programming with LINQ to SQL: Address-Book Case Study (Cont.)

• Click the Address node in the Data Sources window. Click the down arrow to view the items in the list.

– Select the Details option to indicate that the IDE should create a set of Label/TextBox pairs.

• Drag the Address node from the Data Sources window to the Form.


97


• The AddressID is an autoincremented identity column, so set its ReadOnly property to True.

• The database in this example is initially empty, so you’ll need to add several records before testing the find capability.

• To add search functionality, we create controls to allow the user to enter a last name.

• When you enter a last name and click Find, the BindingNavigator is restricted to matches because the data source is changed.


98


• The IDE sets the TextBox’s Text with the DataBindings.Text property.

• Click the plus sign next to (DataBindings) in the Properties window.

• Clicking the drop-down list (as in Fig. 21.31) allows you to choose a BindingSource object and a property to bind.


99


Fig. 21.31 | Data bindings for firstNameTextBox in the AddressBook application .

2009 Pearson Education, Inc. All rights reserved. 1 21 Databases and LINQ to SQL.

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Transcript of 2009 Pearson Education, Inc. All rights reserved. 1 21 Databases and LINQ to SQL.