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 Ch 11: Accessing Data Files  Creating DB files for use by VB  Data control and data-bound controls  Viewing a database table  Using list and combo boxes as bound controls  Adding a lookup table & navigation  Updating a database file

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Visual Basic and Database files  Database formats supported –dBASE, Excel, FoxPro, Lotus –Paradox, text files –With ODBC: SQL server, Oracle, DB2  Database terminology –File, Table, Row –Column, Record, Field –Key field

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Database Terminology  File: collection of tables  Table: consists of rows and columns  Row also known as a record  Field (column): data element of a table  Key field (primary key): unique identifier for row  Current Record: available record

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Creating DBs for use by VB  Cannot use VB Standard Edition or Learning Edition to create new database  You can run the Visual Data Manager add- in that comes with VB –Select Visual Data Manager from the Add-Ins menu –The VisData application window opens

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Using the data control  Data tool (toolbox):  Data control:  Data control on form:

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Data Control (continued)  Set three properties on the Data Control: –Connect-database type (Access) –DatabaseName-name/location of DB –RecordSource-table/query (view) name  Set ReadOnly property to True if you want to prevent updates to database  Next, you can set up data-bound controls

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Data-Bound Control Properties  After placing text boxes, option buttons, etc. on the form, you can bind each control to a column (field) of the table or query whose name is in the RecordSource property.  Set DataSource-point to Data Control  Set DataField-specify Table field

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Viewing a Database File  Design & create the form  Set the properties for the data control  Set the properties for the data-bound controls  Write the code  Run the project

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Navigating the database in code  Data control provides navigation controls  You can hide the data control and provide record movement in code  Recordset object is defined by RecordSource property of Data control  Tip: use App.Path to set DatabaseName property

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Navigating Database (continued)  Using the MoveNext, MovePrevious, MoveFirst, and MoveLast methods –Provide Recordset methods to navigate DB  Recordset has two handy properties called BOF and EOF  BOF set when just before first record or record set is empty  EOF set when just after last record

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Using List & Combo Boxes as Data- Bound Controls  List boxes and combo boxes are data aware  Set up a lookup table for a field by using a combo box  You can bind the combo box to a database field and give the List property initial values

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Lookup Table & Navigation  Modify the user interface  Change the properties  Write the code

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Updating a Database File  Recordset object has an Update method that updates the underlying database  Update occurs automatically when a navigation button is clicked  The AddNew method adds records to DB –All bound controls are cleared –Save with Update method or move off the record

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Deleting Records  Delete method of the Recordset object deletes existing record  After a delete operation, move to another record because deleted record is no longer valid With datBooks.Recordset.Delete.Movenext End with

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Preventing Errors  It is bad form for users to encounter errors  Error Trapping intercepts errors before users see them  Limit user’s action when an operation starts  CancelUpdate method cancels record alteration (add or update) and restores a record to its original form

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