CSE2207/CSE3007Rapid Applications

Programming for Windows

Week 6

Topics

DatabasesVB6.0 and DatabasesThe ADO Data ControlBound controlsThe Recordset Object

Databases

Database An organized collection of data relating to

one main (business) function e.g. Sales, Human Resources, Your Investments, Horse Breeding

Data is held in one or more tables (relations), hence a relational database

Each table is composed of rows and columnseach column represents a fieldeach row represents a record

Each table is a group of related records

Databases Basic Database design steps

Identify the information the user will need from the database (maps to the ER diagram)

Organize the information into 1 or more tables

Establish relationships between tables (if any) Create indexes if necessary Define data validation rules if required

Define/create the database within the DB package itself e.g MSAccess from VB6.0 via the Visual Data Manager

Structured Query Language (SQL)

Manipulating data in a relational database is made easier by using an English-like language called SQL.

The user creates an SQL “query.” The database engine “answers” by returning any database rows that meet the requirements of the query. The query usually contains the tables to search, the columns to return, and other information that sets the scope of the search. "Select Name, Picture from Authors where

Date_of_Birth = #2/7/1947# " This SQL query would return the name and picture of

all authors whose birthday is February 7, 1947. If any rows were returned, you could use bound controls to display the values.

Data Access and VB6.0Business data is stored in numerous formats e.g.

spreadsheets, databases, WP documents, emailMicrosoft have developed UDA to provide a uniform set of

standards for data access: consists of a set of complex interfaces, called OLE DB can deal with any type of data, regardless of storage method or

format In VB 6.0, access to the OLE DB interfaces is through ADO (ActiveX

Data Objects) includes an ADO data provider into ODBC Project|References|Microsoft ActiveX Data Objects 2.0 Library

The BIBLIO.MDB sample database used is located in the main Visual Basic directory (\VB).

Databases and VB6.0

Use the built-in application Visual Data Manager to create and maintain an MS Access db Add-Ins|Visual Data Manager, then File|New etc Right-click Properties, select New Table

For each table name it, define each field, with data type (and

size) create at least a primary index define validation rules for fields if applicable Note: you can’t create a foreign key here

Databases and VB6.0...The Visual Data Manager…

NB!! You cannot modify field sizes, attributes, without losing data

You can add more fields, and change names of existing fields.

Note that default for Zero-Length strings is NO

Use Refresh button to update your table data Utility|Data Form Designer supports creation

of a form with controls that display data from a database

Project|Add Form|Data Form Wizard does too

Databases and VB6.0...

Three approaches:Use the ADO Data Control to provide visual

navigation, data handling and automatic database connection/manipulation, together with bound controls.

Use an invisible/visible ADO Data Control for database connection and manipulation, supplemented with code, and provide your own navigation and data handling, together with bound controls

Handle everything yourself

Approach #1The ADO Data Control Project|Components|Controls|Microsoft ADO Data Control

6.0 (OLEDB) adds the control to the toolbox. Double-click to place it on the form Set its ConnectionString property to link it to a data

provider (e.g. an Access DB) On the General Tab, select Use Connection String

option Then click Build -> Data Link Properties dialog box On Provider tab, select Microsoft Jet……, then Next On the Connection tab browse/enter an Access DB

name Click Test Connection. If ok, then Apply

The ADO Data Control... To create a permanent OLE DB Data Link to a

database: In Windows Explorer move to an appropriate

directory e.g. VB98 Right-click the right pane of Explorer, then New,

then Microsoft Data Link Rename the new file e.g. NorthWind.MDL Right-click the new file, then Properties Complete Dialog box entries for Provider and

Connection tabs as before OLE DB Data Source (Data Link) can also be created

as follows: Control Panel->Data Links icon -> Organise Data Link Files -> New

The ADO Data Control...Set the RecordSource property

On its Property Pages, if Command type is adCmdTable, then select the DB table where the data will come from. If Command type is adCmdText, then type the required SQL Select command in the text box (no ; at the end!)

Now place one or more data-aware controls (text-box, label, datalist etc) on the form, and bind them to the ADO Data Control (i) DataSource property is the name of the ADO Data

Control e.g. adoTitles (ii) DataField property is the name of the table field

which the bound control will display e.g. Title

The ADO Data Control...By default, displays records in entry order

Use a Select…..Order by for the ADO Data Control’s RecordSource property (with commandType property as adcmdText)

Can dynamically change which data is displayed - see Example 1

RecordSource can be an existing QueryDef e.g.ADOQuery.RecordSource = “VicContacts”ADOQuery.Refresh UserName, Password needed if DB is password-

protected Setting Mode to read-only will increase performance

(but user will not be able to change data)

Run the Application

Use the four arrow buttons on the data control to move to the 1st, previous, next or last record in the Recordset

Changes made to values in bound controls are automatically written to the database when the user moves to a new record.

The ADO Data Control...

One data control can access one or many DB tables, depending on the SQL query which it contains Can specify that data will be retrieved

from a single tablevia an existing Stored Procedure in the databasevia SQL you write at design time, or assign at

run-time The user may view, change and add new records, but

not delete records Records returned are held in a ‘Recordset’ object

Fields from the ‘current record’ can be displayed via ‘bound controls’, or referenced in code.

The ADO Data Control...

Use BOFAction, EOFAction to control what happens when user moves past the 1st, last record in the recordset

BOFAction property adDoMoveFirst 0

Keeps the first record as the current record. adStayBOF 1

BOF: Moving past the beginning of a Recordset triggers the Data control Validate event on the first record, followed by a Reposition event on the invalid (BOF) record. At this point, the Move Previous button on the Data control is disabled

Using the EOFAction & BOFAction PropertiesEOFAction property

adDoMoveLast 0Invokes the MoveLast method, positioning the current record at the last record in the recordset and effectively preventing the user from scrolling past the end of the recordset.

adStayEOF 1Positions the current record to the invalid (EOF) record and disables the MoveNext button on the data control.

Using the EOFAction & BOFAction Properties...EOFAction property: adDoAddNew 2

When the user moves past the last record, validates the data in the last record, automatically invokes the AddNew method, and then positions the data control on the new record.

If new data is entered, moving off the current (new) record will automatically trigger an update and save the new record in the database. If the user moves off the new record without adding data, the new record is discarded.

Convenient way of entering many new consecutive records i.e. move to end, then MoveNext, enter data, MoveNext, enter data etc

The Recordset Object Created by the ADO Data control at run-time based

on the CommandType property (e.g. adCmdTable) If the Recordset object contains no records, the BOF

and EOF properties are set to True, and the Recordset object's RecordCount property setting is 0 Any MOVE action will generate an error - so use

the AddNew method to create a valid first record When you open a Recordset object that contains at

least one record, the first record is the current record and the BOF and EOF properties are False.

CursorLocation: adUseClient or adUseServer (default)

The ADO Data Control…

CursorType property Dynamic cursor (adOpenDynamic) allows

additions, changes, and deletions by all users to be viewed

Keyset cursor (adOpenKeyset) behaves like a dynamic cursor, except you cannot see records that other users add,

records that other users delete.

Static cursor (adOpenStatic) provides a static copy of a set of records for you to use to find data or generate reports

Static cursor (adOpenForwardOnly)

Approach #2

Use an invisible/visible ADO Data Control for database connection, manipulation, supplemented with code, and provide your own navigation and data handling controls

1. Create an ADO Data control and link it to a data provider e.g. MS Access database

2. Design form(s) with bound controls to display the data that is retrieved by the ADO Data Control

3. Either make the DC invisible, and provide navigation, tasks via buttons, menu options

OR leave the DC visible (maybe disabled until needed)

Approach #2...

4. Write code to perform navigation (move first, move last etc), validation, deletion, undo changes, add, update

So, use a combination of the ADO Data Control, properties, events,

methods the Recordset object bound controls code

The Data Control…

UpdateControls Method Gets the current record from a Data Control’s

Recordset object and displays the appropriate data in controls bound to the same Data Control Use to restore contents to original values e.g.

when user chooses Cancel

WillChangeRecord Event Occurs just before a record in the underlying

recordset is changed - perform validation (See ex. 2)

MoveComplete Event (See Example 2)

The Recordset Object

Methods (See Example 2) AddNew: add a new, blank record to the end of the

recordset CancelUpdate: cancel changes made to the current

record Delete: Delete the current record from the recordset MoveFirst, MovePrevious, MoveNext, MoveLast Update: Save the changes made to the current

record

Properties BOF, EOF : Beginning, end of the recordset

Searching for Records in a RecordsetFind Method Searches a Recordset for the record that satisfies

the specified criteria. If the criteria is met, the recordset position is set on the found record; otherwise, the position is set on the end of the recordset.

Syntax:

Find (criteria, SkipRows, searchDirection, start)

The comparison operator in criteria may be ">" (greater than), "<" (less than), "=" (equal), or "like" (pattern matching). E.g.

adoDC1.Recordset.Find (”custID = 5”)

Dynamic SQLSub FindContact(strColumn as String, strOperator as

String)Dim strSQL as StringstrSQL = “SELECT * FROM Contacts”strSQL = strSQL & “ WHERE “ & strColumn & strOperatorstrSQL = strSQL & “’” & txtSearch.Text & “’”adoDC1.RecordSource = strSQLadoDC1.RefreshIf adoDC1.Recordset.Recordcount <> 0 Then txtFound.Text = adoDC1.Recordset!ContactElse txtFound.Text = “(Contact Not Found)”End If: End Sub

Recordset Bookmark property

Bookmarks allow you to save a current record pointer and reposition directly to a specific record.

Save the Bookmark into a Variant.Dim vntBookMark as Variant ' Save current vntBookMark = adoDC1.Recordset.Bookmark ’ record pointer.adoDC1.Recordset.MoveFirst ' Move off the

record…adoDC1.Recordset.Bookmark = vntBookmark ' Move back -------------------------------------------------------------------------Private Sub dtlContacts_Click(Area As Integer)adoContacts.Recordset.Bookmark = dtlContacts.SelectedItemEnd Sub

.

Bound Controls

Intrinsic Bound Controls (some)Check Box Image Label Picture

BoxText Box List Box Combo Box OLE Container

Custom Bound Controls (some)DataList DataCombo RichTextBoxDataGrid Masked Edit Microsoft ChartDateTimePicker ImageCombo MonthView May need to add the controls to the toolbox via

Project|Controls tab. All are OLEDB enabled.

Bound Controls

Data-Aware PropertiesDataChanged Indicates whether a value

displayed in a bound control has changed. Not available at design time.

DataSource Specifies the name of the data control to which the control is bound. ANY control with this property can become a ‘bound’ control

DataField Specifies the name of a field in the recordset created by the data control, which this bound control will display

Bound Controls When data is displayed in a bound control, the

DataChanged property is set to False. If the user or any other operation changes the value in the bound control, the DataChanged property is set to True. Simply moving to another record doesn't affect the DataChanged property.

When the data control starts to move to a different record, the WillMove event occurs. If DataChanged is True for any bound control, the data control automatically invokes the Update method to post the changes to the database.

If you don't wish to save changes from a bound control to the database, you can set the DataChanged property to False in the WillMove event.

More Data-Bound Controls...DataList, DataCombo controlsTo use with a single Data Control:

Set DataSource & RowSource to same Data Control e.g. adoTitles

Set DataField & BoundColumn to same field in the data control’s recordset e.g. PublisherID

Can be bound to 2 different DC’s, linking data between them useful in data entry: let the user choose from a list of

Publisher Names, then when they select one, write the corresponding Publisher ID back to the Titles tables

More Data-Bound Controls...Binding DBList/DBCombo to 2 ADO Data Controls:DataSource: The Data Control it is bound to (and which it

will pass data to) e.g. DC1 is linked to the Titles tableDataField: A field in the DataSource recordset. Any list

selection or edit updates this field in the DB e.g. PublisherID in the Titles Table

RowSource: The Data Control whose recordset (a field in it) FILLS the list (e.g. DC2 is linked to Publishers table)

ListField: Name of field in the RowSource recordset (DC2) which will be used to FILL the list i.e. PublisherName

BoundColumn:A field in the RowSource recordset (DC2). Used to map/link to a field in the Datasource recordset (field types must match e.g. PublisherID

More Data-Bound Controls...

DataList, DataCombo: More useful properties SelectedItem property (returns a bookmark) MatchEntry property (controls the way values

are matched in the list) When user selects an item in the list, the

BoundText property becomes updated to the value of the BoundColumn property e.g. if BoundColumn is PublisherID, and user chooses ‘Amazon’ in the list of Publisher Names, then the BoundText would contain the ID for ‘Amazon’

DataGrid control displays editable data in rows, columns

AllowAddNew, AllowDelete, AllowUpdate right-click, then “Retrieve Fields” to display at

design time the fields from its ADO Data Control Then “Edit” to make changes to the display, and

“Properties” to set numerous propertiesDataGrid Control Property Pages: Use General Tab to control user actions (add,

change ..) Use Columns tab to change headings, data field Use Format tab for data formatting Use Layout tab to control column access,visible display

More Data-Bound Controls...

DataGrid control Events:BeforeColUpdate, AfterColUpdate, AfterColEdit

occur when focus is moved to another cell, or to another control in the interface. Use Before… to validate cell contents. Use After… to create other fields/cells based on the

value just entered

BeforeUpdate, AfterUpdate occur ONLY when focus is moved to a cell in another row (record) Use Before… to do final validation on the record as

a whole

Linking the DataGrid to DataList, DataCombo Task: User selects a Publisher Name from a

DataCombo, then display all the books published by that publisher in a DataGrid Set the DataGrid’s DATASOURCE to adoTitles Set CommandType of adoTitles to adCmdText Set the DataCombo’s ROWSOURCE to adoPublishers Set the BoundColumn properties of the DataCombo to

PublisherID, ListField to PublisherName

Dim strSQL As String ‘code for datacombo Change eventstrSQL = “SELECT * FROM Titles WHERE PublisherID = “

_ & dtcNames.BoundText adoTitles.RecordSource = strSQLadoTitles.Refresh

Link Multiple DataGrids

Task: User selects a Publisher row in DataGrid1, then display all the Titles for that Publisher in DataGrid2 Bind each DataGrid to its own ADO Data Control

Private Sub dtgPubTitles_RowColChange(LastRow As Variant, ByVal LastCol As Integer)Dim strSQL As StringstrSQL = “SELECT * FROM Titles WHERE PublisherID _

= ” & adoPublishers.Recordset!PublisherID adoTitles.RecordSource = strSQLadoTitles.Refresh: End Sub