microsoft visual basic 2010: reloaded fourth edition chapter twelve access databases and linq

Microsoft Visual Basic 2010: Reloaded Fourth Edition

Chapter TwelveAccess 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

• 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 2

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


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


Database Terminology (cont'd.)


Figure 12-1: Example of a one-table relational database


• 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




Figure 12-2: Example of a two-table relational database

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


Connecting an Application to a Microsoft Access Database (cont'd.)


Figure 12-3: Data contained in the tblEmploy table



Figure 12-4: How to connect an application to an Access database



Figure 12-5: Result of running the Data Source Configuration Wizard



Figure 12-6: How to preview the contents of a dataset


Figure 12-7: EmployeesDataSet shown in the Preview Data dialog box

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


Binding the Objects in a Dataset (cont'd.)


Figure 12-8: How to bind an object in a dataset

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


Having the Computer Create a Bound Control (cont'd.)


Figure 12-9: Icons in the Data Sources window



Figure 12-10: Result of clicking the tblEmploy table object’s list arrow



Figure 12-11: Result of clicking the Last_Name filed object’s list arrow


• 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




Figure 12-12: Result of dragging the table object to the form


• 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




Figure 12-13: Illustration of the relationships among the database, the objects in the component tray, and the bound controls

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


The DataGridView Control (cont'd.)


Figure 12-14: Task list for a DataGridView control



Figure 12-15: Purpose of each task in the DataGridView’s task list



Figure 12-15: Edit Columns dialog box


• 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




Figure 12-17: DataGridView control after setting some of its properties

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



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

Visual Basic Code (cont'd.)


Figure 12-18: Code automatically entered in the Code Editor window

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



Figure 12-19: How to use the Try…Catch statement

Handling Errors in the Code (cont’d.)


Figure 12-19: How to use the Try…Catch statement (cont’d.)

Handling Errors in the Code (cont'd.)


Figure 12-20: Try…Catch statement entered in the Save Data button’s Click event procedure



Figure 12-21: Sample run of the Morgan Industries application



• 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

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

The Copy to Output Directory Property (cont’d.)


Figure 12-22: How to use the Copy to Output Directory property

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


Binding to an Existing Control (cont'd.)


Figure 12-23: Result of dragging field objects to existing label controls

Binding to an Existing Control (cont'd.)


Figure 12-24: Sample run of a different version of the Morgan Industries application

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



Figure 12-23: How to use the BindingSource object’s Position property


Figure 12-26: How to use the BindingSource object’s Move methods

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

Accessing the Value Stored in a Field


Figure 12-28: How to access the value stored in a field object

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


Creating a Query (cont’d.)


Figure 12-29: How to use LINQ to select and arrange records in a dataset


Figure 12-29: How to use LINQ to select and arrange records in a dataset (cont’d.)


Figure 12-30: How to assign a LINQ variable’s contents to a BindingSource control



Figure 12-31: LINQ code entered in the Find Last Name button’s Click event procedure



Figure 12-32: Employees whose last name begins with the letter S

Personalizing a BindingNavigator Control

• You can include other items on the BindingNavigator control:– Buttons, text boxes, or drop-down buttons


Personalizing a BindingNavigator Control (cont’d.)


Figure 12-33: How to manipulate the items on a BindingNavigator control



Figure 12-34: Items Collection Editor window



Figure 12-35: DropDownButton added to the BindingNavigator control

Using the LINQ Aggregate Operators

• Aggregate operator: returns a single value from a group of values

• Most commonly used aggregate operators:– Average, Count, Max, Min, and Sum



Figure 12-36: How to use the LINQ aggregate operators

Using the LINQ Aggregate Methods (cont'd.)


Figure 12-37: Code associated with the three items on the DropDownButton



Figure 12-37: Code associated with the three items on the DropDownButton (cont’d.)

Adding Items to the BindingNavigator Control (cont'd.)


Figure 12-38: Average pay rate for part-time employees

• Creating the Trivia Game application


Programming Tutorial 1

Figure 12-40: MainForm for the Trivia Game application

• Creating the CD Collection application


Programming Tutorial 2

Figure 12-50: Preview Data dialog box showing the data stored in the CDDataSet


Programming Example

• Cartwright Industries application

Figure 12-55: MainForm in the Cartwright Industries application


Summary

• Can use Visual Basic to access data stored in databases

• Relational database: stores information in tables composed of fields and records

• Primary key: field in a database table that uniquely identifies each record

• Data in a relational database can be displayed in any order, and you can control the amount of information to view


Summary (cont'd.)

• You must connect the application to a database to create a dataset

• Display dataset information by binding controls to dataset objects

• TableAdapter: connects a database to a DataSet object

• BindingSource object: connects a DataSet object to bound controls on a form

• DataGridView control displays data in row and column format


Summary (cont'd.)

• Use a Try…Catch statement to handle exceptions

• Database file’s Copy to Output Directory property: determines when and if the file is copied to the project’s bin\Debug folder

• BindingSource object’s Position property: stores the location of the record pointer in a dataset

• BindingSource object’s Move methods: used to move the record pointer in a dataset

• Can access the value stored in a field object in a dataset

Summary (cont'd.)

• Use LINQ to select and arrange records in a dataset

• LINQ provides Average, Sum, Count, Min, and Max aggregate methods

• Can include additional items such as text boxes and drop-down buttons on a BindingNavigator control


microsoft visual basic 2010: reloaded fourth edition chapter twelve access databases and linq

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