Rapid Applications Programming with Windows

Week 10

Topics Week 10

The Borland Database Engine (BDE)Database DesktopAn Overview of Delphi Database

ComponentsUsing the Database Form Wizard

Data ModulesCreating Database Forms by Hand

Data components Searching for Records

The Borland Database Engine (BDE)

Provides access to local, client/server databases local: (single-tier) all data manipulation

occurs immediately Client/server, two-tier:

client application talks to the database server through database drivers

Database server manages connectionsclient application is responsible for managing

the integrity of the data (validation etc)

The Borland BDE...Client/Server, MultiTier

Client application talks to one or more application Servers, which in turn talk to the database server

Application servers are specialised e.g. data broker, security handler

client app. may be little more than the interface (Thin-client apps). Can be programmed by ‘juniors’

BDE Drivers vary a/c Delphi version STANDARD driver provides access to Paradox,

dBase Other drivers provided for e.g. Sybase, Oracle,

Informix, InterBase, MSAccess95, 97,( NOT 2000) Excel, FoxPro

The Borland BDE...The BDE Administrator utility

The Database Page (tab)displays list of all available DB aliasesan alias provides the path to a DB, and specifies

the driver to usejust change the alias path when changing PC’sAll Delphi database access routines will reference

the DB alias, which then references the DB tablesObject|New to create a new alias, then click

‘Apply’ speed button (or Code Examp1)Save Table As (in Database Desktop) also

displays a list of available aliases

The Borland BDE...

The BDE Administrator utility (contd) The Configuration Page (tab)

Configure the installed drivers: Native, ODBCChange e.g. Block Size, StrictIntegrity, Fill

FactorAdd new ODBC driverChange settings for the System Object:

• INIT settings (for starting an app, stored in Windows Registry)

•Formats settings e.g. Date, Time, Number

Database Desktop Tools|Database Desktop from within Delphi,(or

select as a stand-alone application)

Create a New Table with Database Desktop: File|New Table

Choose Database table type (e.g. Paradox 7) Table details specifications dialog:

Data Type: autoIncrement, Date, Time, Money, OLEValidity Checks: required, Min/max values, defaultsecondary indexesreferential integritypassword access to the field

Database Desktop...

File|Open|Table, then choose alias to a database (e.g. DBDEMOS), then the table

Table|Edit Data to change, add dataTable|Restructure to change table

definitionsFile|Working Directory to specify

directory where the database livesTools/Alias Manager to change,

create aliases (as in BDE Administrator)

Delphi Database Components Non-Visual data access components

Derived from TDataSet class provide mechanism to get at the data via

specific properties:TTable: DatabaseName, TableNameTQuery: DatabaseName, SQLTStoredProc: DatabaseName, StoredProcName

Visual data-aware components (controls) enable user to view, edit the data TDBEdit, TDBListBox, TDBImage, TDBGrid etc

TDataSet components and visual controls communicate via a TDataSource component.

Database Form Wizard

File|New|Business Page ->DataBase Form Wizard OR Database|Form Wizard

Choose between a simple or master/detail form Specify Table, fields, layout for Master info Same for Detail information (use Grid layout) plus

‘link’ fields (usually the foreign key) Run the project, using the Database Navigator

control (similar to the VB Data Control) to access the records.

May need to change component type e.g. an OLE object is displayed as a DBEdit field

Use the form as a starting point, then customise

Database Form WizardOn the final screen, Form Generation ->

Form and DataModule option will store the Dataset component (TTable or TQuery) and the DataSource in a separate module. Allows reuse of those data access

specifications: File|Use Unit DataMod.pas

Can also create a Data Module ‘by hand’ via File|New -> Data Module

In the Data Module’s On Create event handler open the dataset(s) it contains e.g. CustTable.Open

Database Forms, ‘by Hand’

To display data from >1 table, cut/paste all the database components from a ‘wizard-created’ second form to the first form created

Building forms without the Database WizardStart with a TDataset object (TTable or TQuery)

TQuery allows SQL to be written, specifying tables, and fields to be selected

Set its DatabaseName (via an alias), then TableName (for a TTable), or SQL statement (for a TQuery)

Add a RecordSource Object, and point its Dataset property to the TTable/TQuery

Database Forms, ‘By Hand’...

Place appropriate data-aware controls on the form from the Data Controls page (tab) on the component palette

Set their DataSource, DataField properties Set the Active property of the TTable component to

True to see the data at design time (do this last) By default, Delphi creates a TField object for each

field in the DataSet at run-time. You can create these at design time, specifying which fields are to be included in the DataSet, and set their properties: very useful with a DBGrid

Right-click the DataSet object (TTable, TQuery), then Fields Editor

Database Forms, ‘By Hand’…The Fields Editor

Right-click, then Add Fields, and select all the fields from the DataSet which you want to use in your application

Select a field in the Field Editor, to set its properties in the Object Inspector e.g.DisplayLabel, Visible, EditMask, DisplayFormat etc (note the TField component types).

Note that a DBGrid can’t display a BLOB type, so set Visible to False (still available, not visible)

Create new, calculated fields, based on values from the DataSet:

Right-click the Fields Editor, choose New Field Ensure Field Type option button Calculated is

selected

Database Forms, ‘By Hand’…The Fields Editor

Code for the OnCalcFields event (of a DataSet component) (Example 2)

The TTable Object will call the procedure once for each record, so the calculated field will appear for each record in the DBGrid

Lookup fields allow you to place a drop-down list in the grid: limit user to a set of choices determined by a DataSet component

Create a new DataSet component (TTable/TQuery) to be the SOURCE of the data for the drop-down list

Database Forms, ‘By Hand’…The Fields Editor

In the New Field Dialog from the Fields Editor, select Lookup as the field type

Set DataSet to the dataset where the data is COMING FROM

Key Fields e.g. SupplierID in the Stock Table will be used to lookup the SupplierName (Result Field) in the Supplier Table (DataSet), via the SupplierID (LookupKeys) in the Supplier table.

So when the user chooses a supplier name from the drop-down list, its corresponding SupplierID is written to the Stock table when record is updated.

Database Forms, ‘By Hand’...

Finally, make the original DBGrid field (i.e. SupplierID)

not visible To replicate this on another page with a SupplierID,

remove the original DBEdit field (which displayed SupplierID), then drag the SupplierLookup field from the Field Editor to the form

Each TField Object has a Validation Event (Example 3) Filter the Table component records (like a Where

clause) Set Filtered to True Specify the filter: CustNumber = 1234 AND ShipDate < ‘1/1/98’

Database Forms, ‘By Hand’…Finding a RecordFinding Records in a DataSet (Example 4)

Use the FindNearest method (only with a TTable component) for an approximate search. Positions the cursor on the first record that matches the criteria, or on the first record whose values are greater than those specified

Use the FindKey Method for an exact match Both FindNearest and FindKey require IndexName

to be set before the search Locate Method uses an index if available, otherwise

searches sequentially FindKey, Locate return true/false, and position the

cursor on the record if found

Database Forms ‘By Hand’…Referencing dataset records

The TField class represents a field in the database, gives access to its attributes FieldByName Method accesses the field set field’s value with AsString, AsInteger, etc or Value

Table1.FieldByName(‘LastName’).AsString := Edit1.Text; OR

Table1.FieldByName(‘LastName’).Value := Edit1.Text; To Change a field’s value:

Table1.Edit;Table1.FieldByName(‘LastName’).AsString := Edit1.Text;Table1.Post;

Database Forms, ‘By Hand’…Data-aware Components

Data-aware Components Use the ‘Field’ property to access the contents, displayNameEdit.Field.AsString := ‘Clown Fish’; DBGrid

use the Columns property to change the display Options property controls behaviour e.g col. Sizing

DBText: Label, DBEdit: Edit Box DBMemo: Memo

display large text fields If AutoDisplay is False, Double-click to display

the data

Database Forms, ‘By Hand’…Data-aware Components

DBImage: display binary large object data stored in image

format change via Clipboard at design, run-time or via code:

DBImage1.Picture.LoadFromFile(‘clouds.bmp’); DBListBox, DBComboBox

items for selection are specified via the Items property when an item is selected, it is written to the

DataField field in the DataSet DBCheckBox

DBCheckBox1.ValueChecked := ‘On;Yes;True’;

Database Forms, ‘By Hand’…Data-aware Components

DBLookupListBox, DBLookupComboBox Displays a list of values from a lookup field in a

dataset: ListSource, ListField When an item is selected, its value is written to

another field in another dataset: DataSource, DataField

DBCtrlGrid create custom scrollable grid components place any data components on the first cell of the

grid, and Delphi will duplicate those components for each record in the dataset at run-time

Database Forms, ‘By Hand’…Data-aware Components

DBNavigator Allows extensive manipulation of dataset records first, next, previous, last, insert, delete, edit,

cancel edits, post edits, refresh ConfirmDelete, VisibleButtons property Add, remove buttons at design, run-time (Examp.

5) simulate a DBNavigator button-click (Example 6)

Display fly-over help Set ShowHint property to True Use the Hints property String list editor to enter a

separate line of hint text for each button

Database Forms, ‘By Hand’…Dataset programming Providing Default Values, Appending via Code

The DataSet event OnNewRecord fires when an app. inserts or appends a new record into a dataset.

insert your own ‘next’ primary key, today’s date etcprocedure TForm1.Button1Click(Sender: TObject);begin

Table1.Append; //create a new record Table1.FieldByName(‘Name’).AsString := Edit1.text;Table1.FieldByName(‘Age’).AsInteger :=

StrToInt(Edit2.text);Table1.Post;end;

TQuery Components

Use ExecSQL for SQL statements which do not return records:

Query1.SQL.Clear;Query1.SQL.Add(‘insert into CountryTable’);Query1.SQL.Add(‘ (Name, Capital) ‘);Query1.SQL.Add(‘ (values (“Australia”, “Canberra”) ’);Query1.ExecSQL; Can also build up the query as a string, then ‘Add’

the whole stringvar query: stringquery := query + ‘Select * from Orders where ‘; etc

TQuery ComponentsUsing Parameters in SQL statements: At design time, the SQL statement isselect * from CountryTable where name = :ParCountry At run-time e.g. OnChange event of the edit controlWith Query1 dobeginDisableControls;Close;ParamByName(‘ParCountry’).AsString := edtCountry.Text;Open;EnableControls;end;

TQuery components Use the Datasource property to automatically

link to another datasource and access any matched-name fields, which can be used as parameters in the SQL for the Query.

Useful in master/detail forms. E.g. table1/ds1 accesses the customer table, query1/ds2 retrieves orders which match the

custno of the ‘current’ customer record: (custno is a foreign key in the orders table)

set the Datasource of the Query to point to ds1: custno becomes the parameter for the query e.g.

select * from orders, customer where orders.custno = customer.custno

Dataset Programming

Disable the data-aware controls when making changes or performing long operations on the dataset (e.g. loop)

Use a bookmark to keep track of where you started in the dataset

Use a try-finally block to catch exceptions that may occur when reading table data

See Example 8

Tutorial Week 10 Use the tute exercises to become familiar with Delphi 5 Start Delphi Assignment Task 1 (create Paradox DB

tables, add data) Start Delphi Assignment Task 3

Begin with the Database Form Wizard Add, customise to meet task requirements

Note: Because of limited availability of Delphi 5 (K1.07, K1.08, K1.10, B3.46, B3.43, B3.43B, T2.16), and since most of you will not have the software at home, tutes will be used to work on the weekly assignment tasks.

The remaining 4 Tute Exercise marks will be added to the Delphi Assignment, which will now be /14