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Database Applications
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Visual Basic and Database Files
VB projects can display and update the data from database files. VB .NET uses ADO.NET for database access. An advantage of ADO.Net is that information is stored and transferred in Extensible Markup Language (XML). ADO.NET allows the access to database data in many formats including: OleDb, SQLClient for SQL Server (Microsoft’s proprietary DBMS), ODBC, and Oracle. Data from sources such as Access, Oracle, Sybase, or DB2 can be obtained when using OleDb.
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Database Terminology Databases Tables—can be viewed like a spreadsheet
Records (rows) — data for one item, person, transaction Fields (columns) — store a different element of data Key field (unique to each record) Relational database Multiple tables Relationships between the tables To use database files, the standard terminology of relational databases needs to be understood. A database file (with an .mdf or .mdb extension) can hold multiple tables. Most tables use a key field (or combination of fields) to identify each record.
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Database Table Example
Any time a database table is open, one record is considered the current record. As you move from one record to the next, the current record changes.
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HTML Example <html> <head>
<title>Hello World!</title> </head> <body> <h1>Hello world!</h1> <p>This is an HTML document</p> </body> </html>
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XML Example <notes> <note>
<to>Students</to> <from>Instructor</from> <heading>Reminder</heading> <body>Don't forget the exam next week!</body> </note> <note></note> </notes>
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XML Data (1 of 2) Industry-standard format for storing and transferring data The XML needed for accessing databases will be automatically generated in Visual Basic. Data stored in XML is text, identified by tags — similar to HTML tags that can be edited by any text editor program. Tags in XML are not predefined as they are in HTML. Tags can identify fields by name. *Can find specifications at World Wide Web Consortium (W3C)
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XML Data (2 of 2) In addition to an XML data file, there is normally an XML schema file. Schema describes the fields, data types, and any constraints, such as required fields. ADO.NET validates the data against the schema and checks for constraint violations. Schema is defined with XML tags and can be viewed/edited in a text editor. ADO.NET can treat the XML data as objects, allowing the IntelliSense feature of the VS.NET environment to provide information to the programmer. Data handling in XML and ADO.NET executes faster than in earlier forms of ADO.
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Using ADO.NET and Visual Basic
Can display data from a database on Windows Form Web Form Add controls to form and bind data to them. Label, TextBox Special controls designed just for data such as DataGrid, DataList Remember, that controls for a Windows application are different from controls for a Web application and have different properties and events.
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The DataGrid View Control
The DataGridView control is bound to a table in a dataset. The data fields display automatically in the cells of the grid. You must use several classes and objects to set up data access in Visual Basic.
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Data Access in Visual Studio
Allows an easy way to create data-bound controls on a form Can drag tables and fields from the window onto a form to automatically create controls that are bound to the data Data can be displayed in grids or individual fields, referred to as details. Can drag a field from the Data Sources window and drop it on an existing control — causes data binding to be set up automatically. An .xsd file and the schema is added to the Server Explorer window; Binding Source, Table Adapter, and Data Set objects are added to the form’s component tray. To set up data access in VB, several classes and objects are used.
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Overview of Database Objects
Binding Source Establishes a link to the actual data; a specific file and/or server Table Adapter Handles retrieving and updating the data Generates SQL statements that are used to access or update data Dataset Contains actual data — may come from multiple connections and/or multiple data adapters You can add new BindingSource objects using the Data Sources window or the Data menu. No matter where the actual data (the source) for the binding source are, the table adapter transfers data from the source to the dataset (fills) or transfers data from the dataset to the source (updates) all via XML. A dataset is a temporary set of data stored in the memory of the computer. Any controls that you have bound to the dataset will automatically fill with data.
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Steps to Display Data in Bound Controls on a Form
To display database data in bound controls on a form, a binding source, a table adapter, and a dataset are needed.
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Binding Sources Object establishes a link from a specific file or database to the program. Use a wizard to automatically create Binding Source objects –OR— Add new Binding Source objects using the Data Sources window or the Data menu.
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Table Adapters Does all the work of passing data back and forth between a data source (the binding source) and a program (the dataset) Data does not have to be from a database. Data can be text file, object, or an array. Transfers data to and from via XML
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Datasets Temporary set of data stored in memory
In ADO.NET datasets are disconnected; the copy of data kept in memory does not keep an active connection to the data source. Dataset may contain multiple tables and relationships. Any controls bound to the dataset will automatically fill with data. This technique is a big improvement over the recordsets in earlier versions of ADO, which maintain open connections to the data source.
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Grid with Pre-Defined AutoFormat
Predefined formats can be applied from the AutoFormat item on the smart tag.
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The Database Schema File
When a new data source is added to a project, a file .xsd is added to the Solution Explorer — the XML schema definition. XML file contains the description and properties of the data. The schema shows the names of the table(s) and fields, the primary keys for each table, and the relationships among the tables. The TableAdapter for the table, which handles different methods for the table, appears at the bottom of the schema.
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.XSD (Schema) File The .xsd file holds the schema of the database, where table elements, relationships, and keys can be viewed and modified.
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Binding Individual Data Fields
Table fields from the dataset can be bound to many types of controls such as labels, text boxes, combo boxes, and check boxes. Controls that are connected to fields are bound controls or data-bound controls. Easiest way to create bound controls is to use the automatic binding feature of the Data Source window. Creates individual text box controls for each field of data and navigation control allowing the user to more from one record to another *The next slide displays a form with data0bound text boxes.
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Data-Bound Text Boxes — Example
Each text box or check box is bound to one field from the table. As the user clicks the navigation buttons, all controls change to display the data for the next record.
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The Data Sources Window
This window is used to add a new data source by using the Data Source Configuration Wizard. Click the table name to make a drop- down list available to view Details. The table’s icon changes to match the view.
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Selecting Records from a List
Allows user to select records to display from a list Fill a ListBox or ComboBox with values from the database –OR— Display the information in a drop-down list and allow the user to make a selection; the corresponding data elements fill remaining fields. The control type can be selected for a bound control in the Data Sources window. The choices are TextBox, ComboBox, Label, LinkLabel, and ListBox.
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Selecting Fields from the Table
Select individual fields when creating the new data source –OR– after creating the data source. When creating the data source, choose the Add New Data Source option and follow the Configuration Wizard; expand the Tables node and place a check mark on the desired fields. To modify after creating, select the dataset and use the Configuration Wizard and make the field selections from the Wizard. Choose Database Objects, expand the Tables node, and place a check mark on the fields needed. *The next slide displays the Data Source Configuration Wizard.
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Data Source Configuration Wizard
Select only the fields that are to be included in the Data Source Configuration Wizard.
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Choosing the Control Type for Fields
Dragging a Details view to a form displays text boxes for the default text fields. Click a field name and choose a control type in the Data Sources window. You can choose the control type for all controls and then drag the table to the form to create the Details view.
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