Visual Basic Database Access

BICS546

Microsoft Universal Data Access

• OLE DB: The OLE database protocol– Allows a program to access information in any type of data

source, and it is the basis for ADO.– Data provider: databases, spreadsheets, etc.

• ADO: ActiveX Data Objects– An Interface for OLE DB.– Allow programmers to use a standard set of objects to refer

to any OLE DB data source.

• ODBC: Open Database Connectivity– A driver manager– Used for relational databases

Program

ActiveX Data Objects

OLE DBProvider

Data Source

OLE DBProvider

ODBC

ODBCData Source

Using ODBC

• Three types of data source names– User DSN: usable only by you and only on the

machine currently using.– System DSN: Any one using the machine can

use.– File DSN: Can be copied and used by other

computers with the same driver installed.

Visual Basic Database Tools

• Visual Data Manager

• Data Environments

• Data Views

• Data Report Designer

• Data Projects

Visual Data Manager

• Add-Ins/Visual Data Manager

• Supports: Access, dBase, FoxPro, Paradox, ODBC, Text files.

• Creating new database

• Managing existing database

• Query Builder, Form Wizard

• DAO

Data Environments

• Project/More ActiveX Designer/Data Environment

• Data Environments are designed to be the basis of design-time and run-time data access. They make data available to any forms and modules in your application.

Data Environments at Design Time

• Right Click Connection1– Click Properties to set up database connection

– Click Add Command to choose record source.

• Drag and drop fields from Command1 to form. Text box properties:– Data Source: Data Environment1

– Data Member: Command1 (Note: Data environment can support many command objects)

– Data Field

Data Environments at Run Time

• Access command object’s Recordset object and Recordset object’s methods.

• Recordset’s name: rs+command name.– Ex. rsCommand1

• Properties:– EOF, BOF, RecordCount

• Methods:– MoveFirst, MoveLast, MoveNext, MovePrevious

Data Environment Code Example

DataEnvironment1.rsCommand1.MoveNext

IF DataEnvironment1.rsCommand1.EOF THEN

DataEnvironment1.rsCommand1.MoveLast

END IF

Data Views

• View/Data View Window

• An overview of the database objects you have in a project, such as Data Environments, connections, data links.

Data Report Designer

• Project/Add Data Report• Features of Data Report Designer

– Drag and Drop fields from the Data Environment to report detail section. The DataMember and DataField properties of the text box are automatically set.

– Drag and Drop the Command object (Must make sure the DataSOurce and DataMember properties of the DataReport are set properly).

Data Report Code Example

‘To preview report

DataReport1.Show

‘To print

DataReport.PrintReport

Data Projects

• VB projects come with built-in Data Environments and Data Report Designer.

Using Databases in VB

• Three VB database objects:– DAO, RDO, ADO

• Two ways to work with these objects:– VB Data controls, data-bound controls– Programming objects

DAO

• Support the Jet database• DAO data control

– Database property– RecordSource property: tables, queries, SQL

statement– RecordSet Type Property: Table, Dynaset,

Snapshot– Able to connect to data sources such as dBase,

text files, and Excel spreadsheet.

ADO Data Control

• Project/Components/Microsoft ADO 6.0

• Double Click ADO to insert ADO

• Right Click and select ADODC Properties– General : Source of Connection– RecordSource:

• 1 – adCmdText: SQL statement

• 2 – adCmdTable: Table in the database

• 4 - adCmdStoredProc

ADO Properties

• BOF Action, EOF Action• Command TimeOut: Amount of time in seconds

the ADO control will allow for commands to be executed on the server.

• ConnectionString• CursorLocation: server site, client site• CursorType• MaxRecords: 0 means no limit.• RecordSource

Cursor Type

• Forward Only: Can only move forward through the recordset (can only MoveNext). Use the least amount of system resources.

• Static: Can navigate in both directions. Unable to see changes made by other users.

• Keyset: Can see changes made by other users (except insertions).

• Dynamic: Use most of resources, and can see all changes made by other users.

Cursor Lock Type

• ReadOnly

• Optimistic: Does not lock the file until updates are actually applied.

• BatchOptimistic: All changes be submitted at one time.

• Pessimistic: Lock the table the entire time that the recordset is open.

Cursor Mode Property

• Determines the access rights of the user.– Read– Write– ReadWrite– ShareDenyRead: Deny other from opening connections

with read permissions.– ShareDenyWrite– ShareExclusive– ShareDenyNone: Prevent others from opening

conections with any permissions.