TStreams & TFields (LazDataDesktop generated code from Firebird
Database)
lazarus / 16-Databases

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MattStrat · 2015-02-20 14:32

Hi All, I am pretty new to Lazarus & FreePascal. I've been trying it
out over the last week & have some class code generated with the
LazdataDesktop tool that I am getting issues with.
The tool generates 3 classes based on a database table: 1) the
"Object", 2) the "Object Field Map", and 3) the "Object List" along
with their code to load up from datasets, or load the objects up from
their "Object Field Map" .

I've got 2 areas (code generating a TStream property for a Blob field
in the firebird table)  that maybe someone can help me out with (some
sample code below with a test object I have called "Spec"):

1) In the main Object constructor, code generated is:

Code: [Select]//code as generated by DataDesktop Tool
Constructor TMySpec.Create;

begin
  FSPECDATA:=.Create; //error here FSPECDATA is private var for a
TStream
end; 
I get an error illegal expression for the above... So I changed it to
the following and it will compile:

Code: [Select]//code altered by me
Constructor TMySpec.Create;

begin
  FSPECDATA:=TStream.Create; //no error?? not sure if ok?
end;

2) In the code below for the "Object Field Map" in its "DoLoad", I'm
getting a "error-no member SaveToStream" for the FSPECDATA TField  :

Code: [Select] Self.FSPECDATA.SaveToStream(SPECDATA); //error here -
.SaveToStream  looks to be method of a TBlobField?
More code:

Code: [Select]{ TMySpecMap }

  TMySpecMap = Class(TFieldMap)
  Private
    FSPECCODE : TField;
    FSPECDATA : TField; //is a Blob in Firebird, TStream in MySpec
Object
    FSPECNAME : TField;
    Procedure DoLoad(AObject : TMySpec);
  Public
    Procedure InitFields; Override;
    Procedure LoadObject(AObject : TObject); Override;
  end;

Code: [Select]Implementation

{ TMySpecMap }
Procedure TMySpecMap.DoLoad(AObject : TMySpec);

begin
  With AObject do
    begin
    SPECCODE:=GetFromField(Self.FSPECCODE,SPECCODE);
    Self.FSPECDATA.SaveToStream(SPECDATA); //error here -
.SaveToStream  looks to be method of a TBlobField?
    SPECNAME:=GetFromField(Self.FSPECNAME,SPECNAME);
    end;
end;
Can someone let me know proper way to copy my TField (FSPECDATA) data
to the TStream (SPECDATA) property in the above code? The
".SaveToStream" is not a member of TField (though it is a member of
TBlobField I found when searching around)?

Or if there is a better place to ask this please let me know. I've
attached the full unit code zip if that helps.

Thanks!

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balazsszekely · 2015-02-20 15:57

Let's say you have a Blob field named GENERIC_BLOB. This is how you
can read it to stream(or vice versa).

uses db;
var
  st: TStream;
begin
  st := qTest.CreateBlobStream(qTest.FieldByName('GENERIC_BLOB'), 
bmRead); //or bmWrite
end;

Where qTest is the dataset: TSQLQuery, TIBOQuery, TIBOTable, etc...
Please note: This may not work, with zeos component(TZTable, TZQuery).
A few days ago, a user had some issues with zeos and createblobstream.