hs380

Retrieving Existing Objects

Objects that have been stored to the database can be retrieved into memory by using any of the following techniques: If the Id of the object is known the Retrieve constructor can be used.An optional connector through which the object shall be retrieved can be specified. If no connector is specified, the default connector is used.If the object already exists in memory, the existing object is returned.If the object is not found, the constructor returns nil. See example 1.

If the Id of the object is not known or multiple objects meeting a certain criteria need to be retrieved, a Selector or an InstantQuery can be used. See example 2 and example 3.

**Example 1 **

var
  Person: TPerson;
begin
  Person := TPerson.Retrieve('12345678', MyConnector);
  try
    ShowMessage(Person.Name);
  finally
    Person.Free;
  end;
end;

Example 2

var
  I: Integer;
  Person: TPerson;
begin
  with TInstantSelector.Create(nil) do
  try
    Connector := MyConnector;
    Command.Text := 'SELECT * FROM TPerson WHERE Company.Name = "Happy Donuts"';
    Open;
    for I := 0 to Pred(ObjectCount) do
    begin
      Person := Objects[I] as TPerson;
      Person.Salary := Person.Salary * 1.05;
      Person.Store;
    end;
  finally
    Free;
  end;
end;

Example 3

var
  I: Integer;
  Person: TPerson;
begin
  with MyConnector.CreateQuery do
  try
    Command := 'SELECT * FROM TPerson WHERE Company.Name = "Happy Donuts"';
    Open;
    for I := 0 to Pred(ObjectCount) do
    begin
      Person := Objects[I] as TPerson;
      Person.Salary := Person.Salary * 1.05;
      Person.Store;
    end;
  finally
    Free;
  end;
end;