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.