TPgParam raises assertion error when cast as TParam

[yozey]

Hi, even though TPgParam descends from TDAParam which descends from TParam, using the following code raises and access violation with LoadFromFile

Code: Select all

TParam(MyParam).LoadFromFile('somefile', ftBlob); //where MyParam is a TParam

The assertion raised is that the Datatype is not supported. Shouldn't the above method work for a TParam descendant?

[Plash]

TDAParam works with BLOBs in different way then TParam. You cannot use TParam for the ftBlob data type. Some methods in TParam are not virtual and cannot be overriden. So you should use TDAParam or TPgParam.

[yozey]

My issue was a routine that filled TParams with values supplied. Since the routine uses the parent class to allow for usage with most TParam descendants, I could not now enforce a TPgParam/TDaParam as it would limit it to DevArt components.

I found a workaround however using the Assign procedure of TParam.

Code: Select all

var
  Pr: TParam;
begin
  Pr := TParam.Create(nil);
  try
    Pr.Assign(Param); // assign original param properties
    { Fill Pr with some data from supplied stream }
    Param.Assign(Pr); // Reassign data to supplied TParam
  finally
    Pr.Free;
  end;

This has so far worked with 2 different supplied TParam descendants.

[Plash]

This workaround shoud work correctly.