Databases and ADO.NET Programming Right from the Start with Visual Basic.NET 1/e 11

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 2 Objectives Understand databases and the relational database model Understand primary keys and foreign keys Understand simple SQL queries Use WHERE and ORDER BY clauses Query multiple tables using JOIN Create a Connection object

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 3 Objectives (cont.) Create and work with a DataAdapter object Create and work with a Dataset object Work with data bound controls Work with the DataGrid control Develop applications that interact with a database

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall Database Primer A database is a structured collection of data. A field is a storage location for a single piece of information. A record is a complete collection of related fields. A table is a complete set of related records.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall Database Primer (cont.)

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 6 Relational Databases In the relational database model, relationships exist between tables to indicate how the data is connected. Relationships involve the primary key from one table and a foreign key in a related table.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 7 Relational Databases (cont.) The primary key is a field (or set of fields) that uniquely distinguishes the records in a table. The foreign key contains values that match primary key values in a related table. The primary key and foreign key fields are essential for creating the relationships between tables.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 8 Relational Databases (cont.)

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 9 Relational Databases (cont.)

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 10 Relational Databases (cont.) The Customers table and the Orders table have a one-to-many relationship. Students and Classes have a many-to-many relationship. A many-to-many relationship is usually implemented using a linking table with foreign keys to each of the two original tables.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall Structured Query Language (SQL) An application communicates with a DBMS through queries written in a standard language called Structured Query Language (SQL). SQL is an industry standard language that allows an application to communicate with a relational database.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 12 SELECT Query The SELECT command is used to select specific information from one or more tables in a database. –SELECT fields FROM table

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 13 WHERE Clause The WHERE clause provides the database the capability to choose information based on selection criteria. –SELECT fields FROM table WHERE criteria The WHERE clause condition can contain >,, >=, <= LIKE, *, and ? can also be used

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 14 ORDER BY Clause The information returned by a SELECT statement can be arranged in ascending or descending order with the ORDER BY clause. –SELECT fields FROM table [WHERE criteria] ORDER BY field [ASCIDESC] ASC specifies ascending order; DESC specifies descending order.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 15 JOIN To create a query that combines data from multiple tables, you use the JOIN operation. –SELECT fields FROM table1 [LEFT|RIGHT] JOIN table2 ON table1.field1 = table2.field2 [WHERE criteria] [ORDER BY field]

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall Using ADO.NET ADO.NET is the data access architecture for the.NET Framework. ADO.NET provides Connection, Data- Adapter, and Dataset objects to facilitate accessing data in a database.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall Using ADO.NET (cont.)

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 18 Creating a Connection A Connection object establishes a link from your application to a database file. A connection object specifies the type and location of the database file. Step 1: Create a Connection is to select an OleDbConnection control from the Toolbox

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 19 Creating a Connection (cont.) Step 2: Create a Connection is to add an OleDbConnection object to the component tray. Step 3: Select a New Connection for the control. Step 4: Select the appropriate database provider and the path/filename of the database.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 20 Creating a DataAdapter Once a Connection has been established, the next step is to create a DataAdapter. A DataAdapter passes information between the database and your application. The SQL command is part of the DataAdapter.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 21 Creating a DataAdapter (cont.) Step 1: Add an OleDbAdapter control which starts a Wizard Step 2: Specify the Connection to use for the DataAdapter Step 3: Select a Query Type Step 4: Specify the SQL statements Step 5: Save the settings

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 22 Creating a DataAdapter (cont.)

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 23 Generating a Dataset Once you have established a Connection and a DataAdapter, the next step is to create a Dataset. A Dataset in ADO.NET is a temporary, local copy of the information in the table. To create a Dataset, right-click on the object and select Generate Dataset from the pop-up menu.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall Displaying and Navigating Records The information in a Dataset can be viewed by means of one or more data-aware controls. A data-aware control is a control that can be bound to a Dataset; when bound, the control automatically displays the information it receives from the Dataset.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 25 The Fill Method The Fill method of the DataAdapter is used to populate the Dataset. –DataAdapter.Fill(DataSet)

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 26 Dataset Navigation When text boxes are data bound they display their specified field values for the current record in the specified dataset. Each form has a BindingContext object that keeps track of all the data sources associated with the form. The BindingContext has a position property and a Count property.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall The DataGrid Control The DataGrid control is designed to display ADO.NET data in a scrollable grid. The DataSource property specifies the name of the data source from which the grid will get data. The DataMember property specifies which table or other element to bind to if the data source contains more than one bindable element.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 28 Chapter Summary A database is a collection of one or more structured sets of data. A table is a two-dimensional matrix of rows and columns. A foreign key is a field in a table that refers to the primary key in another table.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 29 Chapter Summary (cont.) An application communicates with a DBMS through queries written in SQL. The SELECT command is used to select specific information from one or more tables in a database. The WHERE clause is used to choose information based on selection criteria.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 30 Chapter Summary (cont.) The results of a query can be arranged in ascending or descending order with the ORDER BY clause. Relational databases store data over multiple tables to eliminate data redundancy. A Connection object establishes a link from your application to a database and specifies the type and location of the database.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 31 Chapter Summary (cont.) Once a Connection has been established, the next step is to create a DataAdapter. Once a Connection and a DataAdapter have been established, the next step is to create a Dataset. A Data-aware control is a control that can be bound to a Dataset.

Crews/Murphy – Programming Right from the Start with Visual Basic.NET 1/e – ©2004 Prentice Hall 32 Chapter Summary (cont.) Each form has a BindingContext object that keeps track of all the data sources associated with the form. The DataGrid control is designed to display ADO.NET data in a scrollable grid.

Databases and ADO.NET Programming Right from the Start with Visual Basic.NET 1/e 11