Irwin/McGraw-Hill Copyright© 2000 by the McGraw-Hill Companies, Inc. PowerPoint® Presentation to accompany prepared by James T. Perry University of San Diego

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Ch12: Advanced Data Handling  Write database app. with DB Grid control  Database validation and error-trapping  Locate database records using criteria  Define tables, dynasets, and snapshots  Create database indexes  Create a dynaset using SQL

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Displaying Data in Grids  Using a grid control –Add data control to a form. –Project/Components to add M.S. Data Bound Grid control to toolbox. –Put Dbgrid on form. –Retrieve fields into grid: right-click and then choose Retrieve Fields –Modify grid's properties: Right-click and select Properties

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Displaying Data in Grids (Revised Procdure) (1)  Add new components to the toolbox: –Select Project, Components –Locate and check Microsoft ADO Data Control 6.0 (OLEDB) and Microsoft DataGrid Control 6.0 (OLEDB); close dialog box  Add ADO data control to form & name it adodatbooks  Add DataGrid to form and name it dbgridBooks

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Displaying Data in Grids (Revised Procdure) (2)  Set up Data Source: –Right-click the data control and select ADODC Properties –Click General tab, Click Use Connection String option button –Click Provider tab & select Microsoft Jet 3.51 OLE DB Provider –Click Next button –On the Connection tab, browse to select RnRBooks.mdb

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Displaying Data in Grids (Revised Procdure) (3)  Set up the Data Source continued: –Click the Test Connection button. Dialog box should appear indicating connection succeeded. –Close Data Link Properties dialog box –Click the RecordSource tab; select 2- adCmdTable for Command Type –Select Books from the Table or Stored Procedure drop down list –Close the Property Pages dialog box  Continue with textbook: “ Set the Properties of the Grid ”

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Displaying Record Number & Count  Display record number and record count with RecordCount and AbsolutePosition properties intCurrentRecord = datBooks.Recordset.AbsolutePosition + 1  If at BOF or EOF, AbsolutePosition is 0

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Opening the Database  VB automatically opens a database that has a data control on a form  The open occurs after form load  Use the Refresh method to open a database manually in the Form_Load event procedure  Use the data control’s Reposition event to display the current record number

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Validation and Error Trapping  Lock text boxes by setting their Locked property to True; unlock with False  Usually, you lock the primary key field of a database unless you are adding a record  The Validate event is a good place to check a field’s value  Set the Causes Validation property to True to perform lost focus validation on a field (default is True)

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Trapping Program Errors  Errors may be trapped asynchronously  Visual Basic generates an error number when an error occurs  To handle errors, you must –Turn on error handling feature: On Error... –Create error handling code –Determine what is to be done afterwards

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill The Err Object  The Err object holds info about error that just occurred  Err.Source holds the source of the error  Err.Number holds the error number  Err.Description contains error description  You can raise an error condition--turn on an error--with: Err.Raise Number:=xx

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Coding Error-Handling Routines  On Error statement designates error handler  Code to handle errors follows line label  Line label appears on line by itself and ends with a colon  A Case statement works well to sort out errors with a "switchboard"  Continue execution with Resume statement  Exit statement leaves procedure early

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Recordsets  VB supports three kinds of recordsets: –Table recordset—data from a single table –Dynaset—temporary dataset from a table or query that can be updated –Snapshot—dynaset that cannot be updated  Recordset property set at design time or run time  Search for records with FindFirst, FindLast, FindNext, or FindPrevious methods  Form: datControl.Recordset.Findxxxx criteria where criteria is the search criteria

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Reordering a Table Recordset  By switching indexes, you can view a dynaset or table in different orders  One index displays records in PK order, while another might display records in Title order  Form: datacontrol.Recordset.Index = “Fieldname” where Fieldname is one of the fields  Set to data entry order with: datacontrol.Recordset.Index = “”

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Working with Database Fields  Refer to DB field this way: 1.datControl.Recordset!LastName 2.datControl.Recordset(“LastName”)  Refer to DB field this way: datControl.Recordset(“Pub Date”) Or datControl.Recordset![Pub Date]

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Creating a New Dynaset  Dynaset may be a table or multiple, joined tables  VB uses Structured Query Language (SQL) to create dynasets  SQL is world-wide database access standard  Set the RecordSource property to a SQL string and use Refresh to execute query

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Hands on Programming Example