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Chapter 13: Working with Access Databases and LINQ

Chapter 13: Working with Access Databases and LINQ. Displays records in the Books database Allows the store manager to enter an author’s name (or part of a name) Displays only books written by the author Displays the total value of books in the store.

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Chapter 13: Working with Access Databases and LINQ

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  1. Chapter 13: Working with Access Databases and LINQ

  2. Displays records in the Books database Allows the store manager to enter an author’s name (or part of a name) Displays only books written by the author Displays the total value of books in the store Previewing the Paradise Bookstore Application Figure 13-1 Books written by Carol Smith Figure 13-2 Total value of the inventory Programming with Microsoft Visual Basic 2012

  3. Lesson A Objectives After studying Lesson A, you should be able to: • Define basic database terminology • 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 • Customize a DataGridView control • Handle errors using the Try…Catch statement • Position the record pointer in a dataset Programming with Microsoft Visual Basic 2012

  4. Database Terminology • Computer database • An electronic file containing an organized collection of related information • Relational database • A database that stores information in tables composed of rows and columns • Each column in a table represents a field • Each row in a table represents a record • Field • A single piece of information about a person, place, or thing Programming with Microsoft Visual Basic 2012

  5. Database Terminology (cont.) • Record • A group of related fields that contain all the necessary data about a specific person, place, or thing • Table • A group of related records • Each record in a table pertains to the same topic and contains the same type of information • Primary key • A field uniquely identifying a record • A two-table database has a parent tableand a child table • Foreign key • A field that links a child record to a parent record Programming with Microsoft Visual Basic 2012

  6. Database Terminology (cont.) Figure 13-3 Example of a one-table relational database Figure 13-4 Example of a two-table relational database Programming with Microsoft Visual Basic 2012

  7. Connecting an Application to a Microsoft Access Database • Before an application can access the data stored in a database, it needs to be connected to the database • The connection is made using the Data Source Configuration Wizard • The wizard allows you to specify the data you want to access • The computer makes a copy of the specified data and stores the copy in its internal memory • The copy of the data you want to access is called a dataset Programming with Microsoft Visual Basic 2012

  8. Connecting an Application to a Microsoft Access Database (cont.) Figure 13-5 Data contained in the tblEmploy table Programming with Microsoft Visual Basic 2012

  9. Connecting an Application to a Microsoft Access Database (cont.) Figure 13-6 Choose a Data Source Type screen Figure 13-7 Completed Add Connection dialog box Programming with Microsoft Visual Basic 2012

  10. Connecting an Application to a Microsoft Access Database (cont.) Figure 13-8 Message regarding copying the database file Figure 13-9 Objects selected in the Choose Your Database Objects screen Figure 13-10 Result of running the Data Source Configuration Wizard Programming with Microsoft Visual Basic 2012

  11. Connecting an Application to a Microsoft Access Database (cont.) • Previewing the Contents of a Dataset • You can view the fields and records contained in a dataset by right-clicking the dataset’s name in the Data Sources window and then clicking Preview Data Figure 13-11 Data displayed in the Preview Data dialog box Programming with Microsoft Visual Basic 2012

  12. Binding the Objects in a Dataset • You must bind one or more objects in the dataset to controls in the interface to view dataset contents • Binding • Connecting an object to a control • Bound controls • Connected controls • Types of controls used to bind dataset objects: • Computer-created control • Existing control on the form Figure 13-12 Ways to bind an object in a dataset Programming with Microsoft Visual Basic 2012

  13. Binding the Objects in a Dataset (cont.) Having the Computer Create a Bound Control • When you drag a dataset object onto a form: • The computer creates the control (its type is indicated by an icon) • The dataset object is automatically bound to the control • Example: • Drag the tblEmployee table object to the form • The DataGridView control is created to display tabular data, with rows representing records and columns representing fields • Use the list arrow to change the type of control linked to the object Figure 13-13 Icons in the Data Sources window Figure 13-14 Result of clicking the tblEmploy object’s list arrow Programming with Microsoft Visual Basic 2012

  14. Binding the Objects in a Dataset (cont.) Having the Computer Create a Bound Control (cont.) Figure 13-15 Result of clicking the Last_Name object’s list arrow Figure 13-16 Result of dragging the table object to the form Programming with Microsoft Visual Basic 2012

  15. Binding the Objects in a Dataset (cont.) Having the Computer Create a Bound Control (cont.) • In addition to a control, the computer adds: • BindingNavigator control • To move from one record to the next in the dataset • TableAdapter object • Connects the database to the DataSet object responsible for retrieving data and storing it in the DataSet • TableAdapterManager object • Handles saving data to multiple tables in the DataSet • BindingSource object • Provides the connection between the DataSet and the bound controls Figure 13-17 Illustration of the relationships among the database, the objects in the component tray, and the bound controls Programming with Microsoft Visual Basic 2012

  16. Binding the Objects in a Dataset (cont.) The DataGridView Control • DataGridView control • Displays data in a row and column format • Cell • Intersection of a row and a column • The DataGridView’s task list allows you to add, reorder, and remove columns and set properties of bound columns • AutoSizeColumnsMode property • Has seven settings that control how the column widths are sized • Fill setting • Automatically adjusts the column widths so that the display area of the control is filled Programming with Microsoft Visual Basic 2012

  17. Binding the Objects in a Dataset (cont.) The DataGridView Control (cont.) Figure 13-18 DataGridView control’s task list Programming with Microsoft Visual Basic 2012

  18. Binding the Objects in a Dataset (cont.) The DataGridView Control (cont.) Figure 13-19 Edit Columns dialog box Programming with Microsoft Visual Basic 2012

  19. Binding the Objects in a Dataset (cont.) Figure 13-21 Completed CellStyle Builder dialog box Figure 13-20 Completed Format String Dialog box Programming with Microsoft Visual Basic 2012

  20. Visual Basic Code • When a table or field object is dragged onto a form, the computer also enters code in the Code Editor window • Code in the form’s Load event uses the TableAdapter object to retrieve data • The BindingNavigator’s save event is also coded Figure 13-23 Code automatically entered in the Code Editor window Programming with Microsoft Visual Basic 2012

  21. Visual Basic Code (cont.) Handling Errors in the Code • Exception • An error that occurs while an application is running • Try…Catch statement • Used to intercept exceptions and handle them • Try block • Contains the statements that might fail • Catch block • Contains the code to handle the exceptions Programming with Microsoft Visual Basic 2012

  22. Visual Basic Code (cont.) Handling Errors in the Code (cont.) Figure 13-24 Basic syntax and examples of the Try…Catch statement Programming with Microsoft Visual Basic 2012

  23. Visual Basic Code (cont.) Handling Errors in the Code (cont.) Figure 13-25 Completed Click event procedure for the Save Data button Figure 13-27 Tooltip for the Move last button Figure 13-26 Dataset displayed in the DataGridView control Programming with Microsoft Visual Basic 2012

  24. The Copy to Output Directory Property • Copy to Output Directory property • Determines the way Visual Basic saves changes to a local file • Copy always (default setting) • The database file is copied to the project’s bin\Debug folder each time the application starts • Result: The database file appears in two different folders • Changes to the file in the bin\Debug folder are overwritten • Copy if newer • Preserves run-time changes • Copies over the file in bin\Debug only if it is not current Programming with Microsoft Visual Basic 2012

  25. The Copy to Output Directory Property (cont.) Figure 13-28 Settings for the Copy to Output Directory property Programming with Microsoft Visual Basic 2012

  26. Binding to an Existing Control • You can bind an object in a dataset to an existing control on the form in two ways: • Drag the object from the Data Sources window to the control • Set one or more of the control’s properties in the Properties window • Properties to set depend on the type of control being bound: • DataGridView: Set the DataSource property • ListBox: Set the DataSource and DisplayMember properties • Label or text box: Set the DataBindings /Text property Programming with Microsoft Visual Basic 2012

  27. Binding to an Existing Control (cont.) Figure 13-30 Result of binding a field to an existing control Figure 13-29 A different version of the Morgan Industries application Figure 13-31 First record displayed in the interface Programming with Microsoft Visual Basic 2012

  28. Coding the Next Record and Previous Record Buttons • BindingSource object’s Position property • Stores an invisible record pointer • Positions are integer values  0 • First record is at position 0 • BindingSource object’s Move methods • Can be used to move the record pointer in a dataset to the first, last, next, or previous record in the dataset Programming with Microsoft Visual Basic 2012

  29. Coding the Next Record and Previous Record Buttons (cont.) Figure 13-32 Syntax and examples of the BindingSource object’s Position property Figure 13-33 Syntax and examples of the BindingSource object’s Move methods Programming with Microsoft Visual Basic 2012

  30. Coding the Next Record and Previous Record Buttons (cont.) Figure 13-34 btnNext_Click and btnPrevious_Click procedures Programming with Microsoft Visual Basic 2012

  31. Lesson A Summary • Use the Data Source Configuration Wizard to connect an application to a database • Use the Preview Data command on the Data menu to preview the data in a dataset • Bind an object in a dataset by dragging it to the form and letting the computer create a control, or by dragging it onto an existing control • Use the Fill setting of the DataGridView’s AutoSizeColumnsMode property to have columns fill the display area Programming with Microsoft Visual Basic 2012

  32. Lesson A Summary (cont.) • Use the Dock property of DataGridView to anchor it to the borders of a form • Use the Try…Catch statement to handle exceptions (errors) occurring during run time • Use the BindingSource object’s Position property or its Move methods to move the record pointer while the application is running Programming with Microsoft Visual Basic 2012

  33. Lesson B Objectives After studying Lesson B, you should be able to: • Query a dataset using LINQ • Customize a BindingNavigator control • Use the LINQ aggregate operators Programming with Microsoft Visual Basic 2012

  34. Creating a Query • Query • Specifies records to select from a dataset and the order in which to arrange them • Language Integrated Query (LINQ) • Used to create queries in Visual Basic • Where clause • Contains a condition, or conditions, to limit the records to be selected • Order By clause • Used to arrange the records in ascending or descending order by one or more fields Programming with Microsoft Visual Basic 2012

  35. Creating a Query (cont.) Figure 13-35 Basic LINQ syntax and examples for selecting and arranging records in a dataset Programming with Microsoft Visual Basic 2012

  36. Creating a Query (cont.) Figure 13-36 Syntax and an example of assigning a LINQ variable’s contents to a BindingSource object Programming with Microsoft Visual Basic 2012

  37. Creating a Query (cont.) Figure 13-37 Code entered in the General Declarations section and btnFind Click event procedure Programming with Microsoft Visual Basic 2012

  38. Creating a Query (cont.) Figure 13-38 Employees whose last name begins with the letter S Programming with Microsoft Visual Basic 2012

  39. You can add additional items to a BindingNavigator control to personalize it Button, Textbox, Drop-down button Customizing a BindingNavigator Control Figure 13-39 Instructions for customizing a BindingNavigator control Programming with Microsoft Visual Basic 2012

  40. Customizing a BindingNavigator Control (cont.) Figure 13-40 Items Collection Editor dialog box Programming with Microsoft Visual Basic 2012

  41. Customizing a BindingNavigator Control (cont.) Figure 13-41 DropDownItems property in the Items Collection Editor dialog box Programming with Microsoft Visual Basic 2012

  42. Customizing a BindingNavigator Control (cont.) Figure 13-42 DropDownButton added to the TblEmployBindingNavigator control Programming with Microsoft Visual Basic 2012

  43. Using the LINQ Aggregate Operators • Aggregate operator • Returns a single value from a group of values • LINQ provides several aggregate operators: • Average • Count • Max • Min • Sum Figure 13-43 Syntax and examples of the LINQ aggregate operators Programming with Microsoft Visual Basic 2012

  44. Using the LINQ Aggregate Operators (cont.) Figure 13-45 Message box showing the average pay rate for all employees Figure 13-44 Code entered in each menu item’s Click event procedure Programming with Microsoft Visual Basic 2012

  45. Lesson B Summary • Use LINQ to select and arrange records in a dataset • You can customize the BindingNavigator control by adding additional items to it • LINQ provides aggregate operators that return a single value from a group of values Programming with Microsoft Visual Basic 2012

  46. Lesson C Objectives After studying Lesson C, you should be able to: • Prevent the user from adding and deleting records • Remove buttons from a BindingNavigator control • Add a label, a text box, and a button to a BindingNavigator control Programming with Microsoft Visual Basic 2012

  47. Requirements for the Paradise Bookstore application: Display records from the Books database Allow the store manager to enter an author’s name (or part of a name) to display books by that author The database contains one table: tblBooks It has five fields and 11 records The user should not be allowed to add or delete records You must modify the BindingNavigatorControl to remove the add and delete buttons Completing the Paradise Bookstore Application Programming with Microsoft Visual Basic 2012

  48. Completing the Paradise Bookstore Application (cont.) Figure 13-46 tblBooks table in the Books database Figure 13-47 Completed Items Collection Editor dialog box Figure 13-48 Completed TblBooksBindingNavigator control Programming with Microsoft Visual Basic 2012

  49. Go button’s Click event procedure Displays only records whose Author field starts with the characters entered in the text box If the text box is empty, it displays all records Use the LINQ LIKE operator Total Value button’s Click event procedure Displays the total value of all books in the store Use the LINQ aggregate function SUM Coding the Paradise Bookstore Application Programming with Microsoft Visual Basic 2012

  50. Coding the Paradise Bookstore Application (cont.) Figure 13-49 Books written by authors whose names begin with s Figure 13-50 Message box showing the total value of the inventory Programming with Microsoft Visual Basic 2012

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