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Microsoft Visual Basic 2010: Reloaded Fourth Edition

Microsoft Visual Basic 2010: Reloaded Fourth Edition. Chapter Twelve Access Databases and LINQ. Objectives. After studying this chapter, you should be able to: Define the terms used when talking about databases Connect an application to a Microsoft Access database

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Microsoft Visual Basic 2010: Reloaded Fourth Edition

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  1. Microsoft Visual Basic 2010: ReloadedFourth Edition Chapter Twelve Access Databases and LINQ

  2. Objectives After studying this chapter, you should be able to: • Define the terms used when talking about databases • Connect an application to a Microsoft Access database • Bind table and field objects to controls • Explain the purpose of the DataSet, BindingSource, TableAdapter, TableAdapterManager, and BindingNavigator objects Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  3. Objectives (cont'd.) • Customize a DataGridView control • Handle errors using the Try…Catch statement • Position the record pointer in a dataset • Access the value stored in a field object • Query a dataset using LINQ • Customize a BindingNavigator control • Use the LINQ aggregate methods Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  4. Database Terminology • Computer database: electronic file containing an organized collection of related information • Relational database: database that stores information in tables composed of columns and rows • Field: single item of information • Record: group of related fields • Table: group of related records • Primary key: field that uniquely identifies each record Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  5. Database Terminology (cont'd.) Figure 12-1: Example of a one-table relational database Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  6. Database Terminology (cont'd.) • Parent table: contains a primary key • Child table: contains a foreign key from the parent table to link the tables • Foreign key: field in a table that contains the primary key of another table • Relational database advantages: • Less redundancy • Fast retrieval • Ability to selectively retrieve data Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  7. Database Terminology (cont'd.) Figure 12-2: Example of a two-table relational database Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  8. Connecting an Application to a Microsoft Access Database • Microsoft Access database: • Has a file extension of .accdb • Must connect an application to the database before the application can access the data • Use the Data Source Configuration Wizard to connect to a database • Dataset: copy of the fields and records stored in the computer’s internal memory, which the application can access Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  9. Connecting an Application to a Microsoft Access Database (cont'd.) Figure 12-3: Data contained in the tblEmploy table Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  10. Connecting an Application to a Microsoft Access Database (cont'd.) Figure 12-4: How to connect an application to an Access database Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  11. Connecting an Application to a Microsoft Access Database (cont'd.) Figure 12-5: Result of running the Data Source Configuration Wizard Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  12. Connecting an Application to a Microsoft Access Database (cont'd.) Figure 12-6: How to preview the contents of a dataset Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  13. Figure 12-7: EmployeesDataSet shown in the Preview Data dialog box Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  14. Binding the Objects in a Dataset • Binding: connecting an object in a dataset to a control on a form • Bound controls: controls that are connected to an object in a dataset • Can bind an object to: • An existing control in the interface • A control the computer creates for you Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  15. Binding the Objects in a Dataset (cont'd.) Figure 12-8: How to bind an object in a dataset Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  16. Having the Computer Create a Bound Control • To allow the computer to create a bound control: • Drag the object from the dataset to the form • DataGridView control: displays table data in a row and column format • Use the list arrow next to an object’s name to change the type of control to be created Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  17. Having the Computer Create a Bound Control (cont'd.) Figure 12-9: Icons in the Data Sources window Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  18. Having the Computer Create a Bound Control (cont'd.) Figure 12-10: Result of clicking the tblEmploy table object’s list arrow Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  19. Having the Computer Create a Bound Control (cont'd.) Figure 12-11: Result of clicking the Last_Name filed object’s list arrow Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  20. Having the Computer Create a Bound Control (cont'd.) • BindingNavigator control: • Allows movement to first, last, next, or previous record • Allows direct selection of record by number • Allows you to add or delete a record • Allows you to save changes made to the dataset • Five objects are placed in the component tray: • DataSet, BindingSource, TableAdapter, TableAdapterManager, BindingNavigator Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  21. Having the Computer Create a Bound Control (cont'd.) Figure 12-12: Result of dragging the table object to the form Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  22. Having the Computer Create a Bound Control (cont'd.) • TableAdapter object: connects the database to the DataSet object • DataSet object: stores the information to be accessed from the database • TableAdapterManager object: handles saving data to multiple tables in the DataSet • BindingSource object: connects the DataSet object to the bound controls on the form Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  23. Having the Computer Create a Bound Control (cont'd.) Figure 12-13: Illustration of the relationships among the database, the objects in the component tray, and the bound controls Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  24. The DataGridView Control • DataGridView control: displays data in a row and column format • Each row represents a record • Each column represents a field • Cell: the intersection of a row and column • DataGridView has a task list used to control its appearance and behavior Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  25. The DataGridView Control (cont'd.) Figure 12-14: Task list for a DataGridView control Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  26. The DataGridView Control (cont'd.) Figure 12-15: Purpose of each task in the DataGridView’s task list Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  27. The DataGridView Control (cont'd.) Figure 12-15: Edit Columns dialog box Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  28. The DataGridView Control (cont'd.) • Many properties of DataGridView are listed only in the Properties window • AutoSizeColumnsMode property: • Select Fill setting to automatically adjust column widths to exactly fill the display area • Select ColumnHeader setting to adjust column widths based on the header text Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  29. The DataGridView Control (cont'd.) Figure 12-17: DataGridView control after setting some of its properties Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  30. Visual Basic Code • DataGridView control allows data to be edited directly within the control to update the database • Two event procedures are automatically created in Code Editor window when a table or field object is dragged to the form • MainForm_Load • bindingNavigatorSaveItem_Click • MainForm_Load event: • Fill method: TableAdapter object’s method to retrieve data from the database and store it in the dataset Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  31. Visual Basic Code (cont'd.) • bindingNavigatorSaveItem_Click event: • Saves any changes made to the dataset • EndEdit method: applies pending changes to the dataset • UpdateAll method: commits the dataset changes to the database • Be sure to use error-handling code Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  32. Visual Basic Code (cont'd.) Figure 12-18: Code automatically entered in the Code Editor window Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  33. Handling Errors in the Code • Exception: an error that occurs while an application is running • VB “handles” errors if the program does not by showing an error message and terminating the application • Try…Catch statement: used to trap errors and attempt to handle them • Place code that could cause an exception within the Try block • Catch block is executed if an exception occurs Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  34. Figure 12-19: How to use the Try…Catch statement Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  35. Handling Errors in the Code (cont’d.) Figure 12-19: How to use the Try…Catch statement (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  36. Handling Errors in the Code (cont'd.) Figure 12-20: Try…Catch statement entered in the Save Data button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  37. Handling Errors in the Code (cont'd.) Figure 12-21: Sample run of the Morgan Industries application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  38. Handling Errors in the Code (cont'd.) • BindingNavigator control provides buttons for first, last, previous, and next record and for adding records, deleting records, and saving changes • Can also use the control to access a record by its record number Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  39. The Copy to Output Directory Property • Local database file: database file contained in a project • Copy to Output Directory property:determines how VB saves changes to a local database file • Copy always setting: database file is copied from the project folder to bin\Debug folder each time the application is started • Changes are made only to the bin\Debug copy • Copy if newer setting: newer of the two database files (project folder and bin\Debug folder) is saved in bin\Debug folder Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  40. The Copy to Output Directory Property (cont’d.) Figure 12-22: How to use the Copy to Output Directory property Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  41. Binding to an Existing Control • Can bind an object in a dataset to an existing control in two ways: • Drag an object in the dataset to a control on the form • Select the control and set properties • Properties to bind the control are specific to the control • DataSet, BindingSource,TableAdapter, and TableAdapterManager objects are added to the component tray • BindingNavigator control is NOT added automatically Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  42. Binding to an Existing Control (cont'd.) Figure 12-23: Result of dragging field objects to existing label controls Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  43. Binding to an Existing Control (cont'd.) Figure 12-24: Sample run of a different version of the Morgan Industries application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  44. Coding the Next Record and Previous Record Buttons • BindingSource object uses an invisible record pointer to track the current record in the dataset • Position property: stores position of current record; this position number is zero-relative • Move method: moves the record pointer’s position to first, last, previous, or next record in the dataset Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  45. Figure 12-23: How to use the BindingSource object’s Position property Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  46. Figure 12-26: How to use the BindingSource object’s Move methods Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  47. Coding the Next Record and Previous Record Buttons (cont'd.) Figure 12-27: Code entered in the Click event procedures for the Next Record and Previous Record buttons Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  48. Accessing the Value Stored in a Field Figure 12-28: How to access the value stored in a field object Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  49. Creating a Query • Can arrange records in a dataset in any order • Query: specifies the records to select in a dataset • Language Integrated Query (LINQ): language used to create a query • Where clause: optional, specifies a condition to limit which records to view • Order By clause: optional, specifies whether to arrange in descending or ascending order • Option Infer On: allows computer to infer the data type from the variables in the query Microsoft Visual Basic 2010: Reloaded, Fourth Edition

  50. Creating a Query (cont’d.) Figure 12-29: How to use LINQ to select and arrange records in a dataset Microsoft Visual Basic 2010: Reloaded, Fourth Edition

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