WhiteUnicorn

	#WhiteUnicorn/ StartPage/ Documentation/DelphiFAQ >

Frequently Asked Questions

Creating a Lookup field at runtime

Question:

How can I create a lookup field at runtime?

Answer:

Creating a lookup field at runtime differs in only a few ways from

creating any standard TField object.  Three properties of a field

that must be set in order to function as a Lookup field are 

LookUpDataset, LookUpKeyFields and LookUpResultField.  The sample 

code below demonstrates how to create a Lookup field at runtime 

using the two DBDEMOS tables 'customer.DB' and 'orders.DB'.

 

Example:



uses

  Forms, Classes, Controls, StdCtrls, Db, DBTables, DBCtrls;





type

  TForm1 = class(TForm)

    Table1: TTable;   // DBDemos customer table

    Table2: TTable;   // DBDemos orders table

    Button1: TButton;

    DBLookupComboBox1: TDBLookupComboBox;

    DataSource1: TDataSource;

    Table2CustNo: TFloatField;  // CustNo key field object used for Lookup  

    procedure Button1Click(Sender: TObject);

  private

    { Private declarations }

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.DFM}



procedure TForm1.Button1Click(Sender: TObject);

begin

  with TStringField.Create(Table2) do begin

    FieldName := 'MyLookup';

    FieldKind:= fkLookup;

    DataSet := Table2;  

    Name := Dataset.Name + FieldName;

    KeyFields:= 'CustNo';

    LookUpDataset:= Table1;

    LookUpKeyFields:= 'CustNo';

    LookUpResultField:= 'Company';

    DbLookupCombobox1.DataField:= FieldName;

    DataSource1.DataSet:= Dataset;

    Table2.FieldDefs.Add(Name, ftString, 20, false);

  end;

  DbLookupCombobox1.DataSource:= Datasource1;

  Table1.Active:= True;

  Table2.Active:= True;

end;



end.

	#WhiteUnicorn/ StartPage/ Documentation/DelphiFAQ >

	Anastasija aka WhiteUnicorn	LiveJournal PhotoFile