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Transcript
Chapter 9 Working with Databases Introduction • In this chapter you will learn: – Basic database concepts – How to write Visual Basic applications that interact with databases – How to use a DataGridView control and display the data in a database – How to sort and update database data – To create an application that displays database data in list boxes, text boxes, labels, and combo boxes Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 2 Section 10.1 DATABASE MANAGEMENT SYSTEMS Visual Basic applications use database management systems to make large amounts of data available to programs. Layered Approach to Using a DBMS • Applications that work with a DBMS use a layered approach – VB application is topmost layer – VB sends instructions to next layer, the DBMS – DBMS works directly with data • Programmer need not understand the physical structure of the data – Just need to know how to interact with the database Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 4 Visual Basic Supports Many DBMS’s • Visual Basic can interact with many DBMS’s – Microsoft SQL Server – Oracle – DB2 – MySQL Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 5 Section 10.3 DATAGRIDVIEW CONTROL The DataGridView control allows you to display a database table in a grid. The grid can be used at runtime to sort and edit the contents of a table. Connecting to a Database • Visual Basic uses a technique called Data binding to link tables to controls on forms • We will use these data-related components: – A Data source is usually a database • Can include text files, Excel spreadsheets, XML data, and Web services – A Binding source connects data bound controls to a dataset – A Table adapter pulls data from the database and passes it to your program • Uses Structured Query Language (SQL) is used to select data, add new rows, delete rows, and modify existing rows – A Dataset is an in-memory copy of data pulled from database tables Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 7 Connecting to a Database • The flow of data from database to application – Data travels from data source to application – Application can view/change dataset contents – Changes to dataset can be written back to the data source Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 8 Section 10.4 DATA-BOUND CONTROLS Some controls can be bound to a dataset. A data-bound control can be used to display and edit the contents of a particular row and column. Advantages of Data-Bound Controls • Can bind fields in a data source to controls: – Text boxes – Labels – List boxes • Contents of data-bound controls change automatically when moving from row to row • Data-bound controls also allow the contents of a database field to be changed Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 10 Adding a New Data Source • Open the Data Sources window and click the Add New Data Source link • Follow the steps in the Data Source Configuration Wizard to create a connection to the database Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 11 Deleting a Data Source • A data source named Employees for example would be defined by a file named Employees.xsd • To delete this data source: – Select Employees.xsd file in Solution Explorer – Press Delete on the keyboard Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 12 Binding the Data Source to a DataGridView Control • Drag and drop an existing dataset from the Data Sources window to an open area on the form – For example: Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 13 Binding the Data Source to a DataGridView Control • At the same time Visual Studio builds a DataGridView on the form, it adds a number of important objects to the form’s component tray: – – – – – The BindingNavigator creates a ToolStrip at the top of the form The DataSet is an in-memory copy of the table The BindingSource connects the DataGridView to the DataSet The TableAdapter pulls data from the database into the DataSet The AdapterManager is a tool for saving data in related tables Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 14 Binding Individual Fields to Controls • Use the dataset in the Data Sources window – Select Details from the table drop-down list – Drag table to an open area of a form – Creates a separate control for each field – Can also drag columns individually • • • • Text and numeric fields added as text boxes Yes/No fields added as checkboxes DateTime fields use DateTimePicker controls May wish to change some control properties Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 15 Adding Rows to a Database Table • A TableAdapter provides an easy way to add a row to a database table • To find the TableAdapter you must open a data set’s Schema Definition • A schema definition file (.xsd) was automatically created in Tutorial 10-5 for the Members table Dataset – Displays the names and data types of fields in the table Copyright © 2011 Pearson Addison-Wesley • To edit the schema definition file: – Double-click its name in the Solution Explorer window – An editor window will open • A TableAdapter object was automatically created for the Members DataTable • Each DataTable has a TableAdapter associated with it Chapter 10 – Slide 16 Adding Rows to a Database Table • A TableAdapter object has an Insert method – Used to add a new row to the database table – Each column is an argument of the method – Just provide the values for each argument – For example: MembersTableAdapter.Insert(10, "Hasegawa", "Adrian", "305-999-8888",#5/15/2010#) Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 17 Identity Columns • Some database tables have an identity column – Assigned a unique number by the database – Occurs automatically for identity columns – No need to manually supply a value for this column • Payments table uses an identity column – Omit ID column value – Only supply Member_Id, Payment_Date, and Amount PaymentsTableAdapter.Insert(5, #5/15/2010#, 50D) Copyright © 2011 Pearson Addison-Wesley Chapter 10 – Slide 18