Visual Basic 6.0 Handout 5 Deere & Company

Transcription

1 Visual Basic 6.0 Handout 5 Deere & Company

2 Sree Nilakanta Page 2 02/03/99 Handout 5 Database Programming Visual Basic is perhaps one of the easiest languages to integrate database programming. VB can easily work with a number of different relational databases such as Access, SQL Server, Oracle, etc. VB offers multiple ways to achieve this objective. At the simplest, you use the data control to connect to an external database. The database could be Access or any number of other ODBC (open database connectivity) compatible databases. At the complex (actually this turns out to be the easiest), one could use the OLEDB connection to link up with a number of different data sources. In our first example, we will build a project to link up to an Access database, namely, the Northwind example database. The following steps will build this project. Step 1 As usual we start a new project and name our form frmcategories and give it a caption Categories File. We add a data control to the form and name it datcategories and caption it Categories. Stretch out the control to fill the width of the form. Note that the connection is defaulted to Access. Step 2 Set the database name to Nwind.mdb. This database is available on the vb98 directory. Select Categories from the drop down list on the RecordSource property. We will be using this record source for our project. That is all there is to connect and use an Access database! Step 3 Connecting to a database and selecting a record source is not enough to get us going. We need to pull data into fields on the form. Many of the form controls (labels, text boxes) are data aware and can be designed to display or hold the values of data from these databases. Let us define some labels and text boxes that are data aware. See the enclosed source code for details. Step 4 We will bind the label lblcategoryid, txtcatname, and txtdescription to the data fields of Category ID, category name, and description of the data source datcategories. Description text box is set to take multiple lines. Run the program. You can move up and down the data file using the arrows on the data conrol. Your application will look like this.

3 Sree Nilakanta Page 3 02/03/99 Figure 1 Application UI The source files are available at for download. Database Applications using Data Form Wizard Visual Basic allows a programmer or power user to develop database applications without having the full blown database software. As we saw in the previous example, the VB application used an Access database even though there may not be an Access package. All you needed was a link to the access database file. The Data Form Wizard is one of many such tools that are part of the VB package whose purpose is to reduce the programming burden. Using the DFWizard, you can easily automate the creation of a front end database application. Step 1 Start a new project. Click on the Add-Ins menu choice and select the Add-In Manager option. Figure 2 shows the dialog window you should see. Choose the VB 6 Data Form Wizard by clicking. Press OK to accept. If everything worked as advertised, the dialog will close uneventfully. Click on the Add-Ins menu and you should see a new menu item in the pull down list. It should be named Data Form Wizard We will use this in our project now. Step 2 Click on the Data Form Wizard option of the Add-Ins menu. Skip the first dialog box by pressing the Next button. This is an introductory dialog. You will now see a dialog that asks you to select a database type. Choose Access. Click on the Next to go to the next dialog. Chose the Nwind.mdb file. As shown in the example below, the Nwind.mdb database files are located in the vb98 subdirectory. If you do not find it there search and locate using the Find tool of your operating system. Once found, select it for the database name. If you select the checkboxes for Tables and Queries

4 Sree Nilakanta Page 4 02/03/99 then all tables and queries available within the NorthWind database will be available here as well. The database selection dialog is shown in Figure 3 below. Figure 2 The Add_in Manager dialog Figure 3 The Database dialog

5 Sree Nilakanta Page 5 02/03/99 Step 3 Click on the Next button to get to the next dialog where we will choose a layout for the data. Three layout choices are available. Single record, a data grid, a Master/Detail, MS HflexGrid, and MS Chart layout are presented. We will choose the single record layout. The next dialog then shows all of the attributes (fields) of the Categories table (we chose the categories table from the record source list box). We also choose the ADO Data Control for our data access. Figure 4 The Layout Dialog Step 4 Choose the Categories record source and click on the double arrow to select all of the fields to be included on the form. Figure 5 shows the resulting dialog. Step 5 We are now done with the Record Source dialog. Click on the Next button to progress to the Control Selection dialog. This dialog allows you to decide which if several command buttons you want to appear in your form. They are selected by default. Figure 6 shows the dialog. Step 6 The next dialog allows you to give your form a name and to save the current settings as default so that you can create additional forms using the same settings.

6 Sree Nilakanta Page 6 02/03/99 Wizard Options Name box Lets you give a meaningful name to your saved project. The default is (None). If you chose (None), your project will not be saved. Figure 5 Record Source & Fields dialog Displays the Save Profile dialog box where you can name and select a location in which to save your settings. Note Your application will be saved in memory but not on your disk unless you use the Save Project command on the File menu after the application is created. Step 7 Though we finshed working with the Data Form Wizard, our task is not quite complete. The wizard created a data form with all the necessary data bound fields and properties. The data bound controls appear on a second form window called Categories. You can resize this form to suit your taste as well as to give the picture box enough space to display images. If we try to execute the project nothing seems to happen as the empty form takes center stage. Alos, we do not even see the data form!

7 Sree Nilakanta Page 7 02/03/99 Figure 6 Control Selection dialog Step 8 Click on the Project menu and select Project 1 Properties to bring up a Project Properties dialog. Choose Categories from the Startup Objects list and press OK. This ensures that our stratup form is the data form. We really do not use the Form1. We can remove it from the project. Highlight Form1 in the Project explorer and select Remove Form1 from the project menu. The source files can be found at for download. Note: The material on data controls and database programming can be found in Chapter 13 of your book.

8 Sree Nilakanta Page 8 02/03/99 Figure 7 Project Properties dialog