Irwin/McGraw-HillIrwin/McGraw-Hill Copyright© 2000 by the McGraw-Hill Companies, Inc.

PowerPoint® Presentationto accompany

prepared byJames 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

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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”

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Displaying Record Number & Count

Display record number and record count with RecordCount and AbsolutePosition propertiesintCurrentRecord = datBooks.Recordset.AbsolutePosition + 1

If at BOF or EOF, AbsolutePosition is 0

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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

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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

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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

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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 = “”

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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”)

OrdatControl.Recordset![Pub Date]

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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

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Hands on Programming Example