CSCI 3328 Object Oriented CSCI 3328 Object Oriented Programming in C# Programming in C#

Chapter 12: Databases and LINQChapter 12: Databases and LINQ

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Xiang Lian

The University of Texas – Pan American

Edinburg, TX 78539

lianx@utpa.edu

Objectives

• In this chapter, you will– Learn the relational database model– Get familiar with using LINQ to retrieve and

manipulate data from a database– Know how to add data sources to project, create

LINQ to SQL classes, and use data binding to move data between GUI controls and databases

– Learn how to create Master/Detail views to select a record and display its details

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Introduction

• A database is an organized collection of data• A database management system (DBMS)

provides mechanisms for storing, organizing, retrieving and modifying data

• Existing DBMSs– Microsoft SQL Server– Oracle– Sybase– IBM DB2

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Introduction (cont'd)

• PostgreSQL and MySQL are popular open-source DBMSs that can be downloaded and used freely by anyone

• We use Microsoft’s free SQL Server Express, which is installed with Visual Studio

• It can also be downloaded separately from Microsoft (www.microsoft.com/express/sql)

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Relational Database

• A relational database organizes data simply in tables– rows (also called records)– columns (also called fields, attributes)

• Primary key: a column (or group of columns) requiring a unique value that cannot be duplicated in other rows

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

• Foreign key—a column in this table that matches the primary-key column in another table

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Example of Table: Employees

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SQL

• A program might select data from the table to create a query result – E.g., to retrieve the location of each department, in

increasing order by Department number– SQL:

• SELECT DISTINCT Department, Location

FROM Employees

ORDER BY Department

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SQL Results

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Schema

• A database may contain one or multiple tables• A database’s tables, their fields and the

relationships among them are collectively known as a database schema

• In SQL Server, database files have the *.mdf (“master data file”) file-name extension– Books.mdf– http://media.pearsoncmg.com/ph/esm/deitel/vcs2008ht

p3e/examples/

– Chapter 219

Entity-Relationship Model

• Entity-Relationship (ER) model– Entity

• Authors

• Titles

– Relationship• There is a one-to-many relationship between a primary

key and a corresponding foreign key– E.g., one author can write many books and one book can be

written by many authors

• Others: many-to-many or one-to-one relationship

• E.g., AuthorISBN10

Books Database

• Books database consists of 3 tables– Authors– Titles– AuthorISBN

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Example of ER Diagram

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Books database

Authors

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Titles

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AuthorISBN

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SQL on Books Database

• SELECT * FROM tableName– SELECT * FROM Authors

– SELECT AuthorID, LastName FROM Authors

• SELECT columnName1, columnName2, … FROM tableName WHERE criteria– SELECT BookTitle, EditionNumber, Copyright

FROM Titles

WHERE Copyright > '2011'

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SQL on Books Database (cont'd)

• Operator LIKE is used for pattern matching– Wildcard character

• Percent (%): zero or more characters

• Underscore (_): a single wildcard character

– SELECT AuthorID, FirstName, LastName

FROM Authors

WHERE LastName LIKE 'D%'

– SELECT AuthorID, FirstName, LastName

FROM Authors

WHERE LastName LIKE '_y%'

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Deitel

Ayer

SQL on Books Database (cont'd)

• SELECT columnName1, columnName2, … FROM tableName ORDER BY column ASC– ASC– DESC– SELECT AuthorID, FirstName, LastName FROM Authors ORDER BY LastName DESC

• Other statements in SQL– table1 INNER JOIN table2 ON table1.columnName=table2.columnName– INSERT INTO tableName (columnName1, columnName2, … ) VALUES (value1,

value2, …)– UPDATE tableName SET columnName1 = value1, columnName2 = value2, …

WHERE criteria– DELETE FROM tableName WHERE criteria

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Querying a Database with LINQ

• Connect to the Books database• Create the LINQ to SQL classes required to

use the database• Add the Authors table as a data source• Drag the Authors table data source onto the

Design view to create a GUI for displaying the table’s data

• Add a few statements to the program to allow it to interact with the database

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GUI To Display Authors Table

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Creating LINQ to SQL Classes

• Step 1: Creating the project– Create a new Windows Forms Application named

DisplayTable– Change the name of the source file to

DisplayAuthorsTable.cs– The IDE updates the Form’s class name to match

the source file– Set the Form’s Text property to "Display Table"

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Creating LINQ to SQL Classes (cont'd)

• Step 2: Adding a database to the project and connecting to the database– To interact with a database, you must create a

connection to the database in the Visual Studio• Select View > Server Explorer to display the Server

Explorer, and click Connect to Database icon button• Or, select Tools > Connect to Database…• In Choose Data Source dialog, select Microsoft SQL

Server Database File from the Data source• If you check Always use this selection CheckBox, the

IDE will use this type of database file by default when you connect to databases

• Click Continue to display the Add Connection dialog22

Choose Data Source Dialog

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Creating LINQ to SQL Classes (cont'd)

• In the Add Connection dialog– click the Change… Button to select a database– click Browse… Button to locate and select the

Books.mdf file in the Databases directory– click Test Connection Button to verify that the

IDE can connect to the database through SQL Server Express

– click OK to create the connection

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Add Connection Dialog

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Creating LINQ to SQL Classes (cont'd)

• Step 3: Generating the LINQ to SQL classes– Select the database from which the LINQ to SQL

classes will be created– LINQ to SQL uses the database’s schema to help

define the classes– Right click the project name in the Solution

Explorer and select Add > New Item… to display the Add New Item dialog

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

– The Object Relational Designer window will appear• Double click the Books.dbml file in the Solution

Explorer to open the Object Relational Designer26

Object Relational Designer

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Creating LINQ to SQL Classes (cont'd)

• Expand the Books.mdf database node in the Server Explorer

• Expand the Tables node• Drag the Authors, Titles and AuthorISBN tables onto

the Object Relational Designer• The IDE prompts whether you want to copy the

database to the project directory• Select Yes

– The Object Relational Designer will display the tables that you dragged from the Server Explorer

• Save the Books.dbml file28

Object Relational Designer (cont'd)

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Recall: Querying a Database with LINQ

• Connect to the Books database• Create the LINQ to SQL classes required to

use the database• Add the Authors table as a data source• Drag the Authors table data source onto the

Design view to create a GUI for displaying the table’s data

• Add a few statements to the program to allow it to interact with the database

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Data Bindings Between Controls and the LINQ to SQL Classes

• Step 1: Adding the Authors LINQ to SQL class as a data source– To use the LINQ to SQL classes for data binding, you

must first add them as a data source• Select Data > Add New Data Source… to display the Data

Source Configuration Wizard• The LINQ to SQL classes are used to create objects

representing the tables in the database, so we will use an Object data source. In the dialog, select Object and click Next >

• Expand the tree view and ensure that Author is checked. An object of this class will be used as the data source

• Click Finish31

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Data Bindings Between Controls and the LINQ to SQL Classes

(cont'd)• The Authors table in the database is now a

data source that can be used by the bindings

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

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Data Bindings Between Controls and the LINQ to SQL Classes (cont'd)

• Step 2: Creating GUI elements– Use the Design view to create a GUI control that can

display the Author table’s data• Switch to Design view for the DisplayAuthorsTable class

• Click the Author node in the Data Sources window—it should change to a drop-down list.

– Open the drop-down by clicking the down arrow – Select DataGridView option—this is the GUI control that will be

used to display and interact with the data.

• Drag the Author node from the Data Sources window onto the Form in Design view

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Data Bindings Between Controls and the LINQ to SQL Classes (cont'd)

• To make the DataGridView occupy the entire window– select the DataGridView

– use the Properties window to set the Dock property to Fill

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Data Bindings Between Controls and the LINQ to SQL Classes (cont'd)

• Step 3: Connecting the BooksDataContext to the AuthorBindingSource– The final step is to connect the

BooksDataContext to the AuthorBindingSource, so that the application can interact with the database

– Obtain data from the database and to save any changes that the user makes to the data back into the database (see next slide)

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Data Bindings Between Controls and the LINQ to SQL Classes (cont'd)

• Creating BooksDataContext– private BooksDataContext database = new

BooksDataContext();

• Connection between BooksDataContext and AuthorBindingSource– authorBindingSource.DataSource = from author in

database.Authors orderby author.AuthorID select author;

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Data Bindings Between Controls and the LINQ to SQL Classes (cont'd)

• Step 4: Saving Modifications Back to the Database– If the user modifies the data in the DataGridView,

we’d also like to save the modifications in the database– By default, the BindingNavigator’s Save Data Button

is disabled– To enable it, right click this Button’s icon and select

Enabled to true– Then, double click the icon to create its Click event

handler– Saving the data entered into the DataGridView back to

the database is a three-step process

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• Validate();• authorBindingSource.EndEdit();• database.SubmitChanges();

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click event

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