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Delphi 10.3.2 enterprise, database ASA (SQL Anywhere 17.0.9.4913).

I have this table

CREATE TABLE string_null(
    lo_key integer NOT NULL DEFAULT AUTOINCREMENT PRIMARY KEY,
    str_short char(100) NOT NULL DEFAULT '',
    str_long long varchar NOT NULL DEFAULT '');

and I want to insert records using FireDAC TFDConnection and TFDQuery components.

qry.Insert;

If I assign non-empty strings, everything works properly.

qry.FindField('str_short').Asstring := 'ABC';
qry.FindField('str_long').Asstring := 'XYZ';

If I insert a record using empty strings (empty, not null!)

qry.FindField('str_short').Asstring := '';  // IsNull is FALSE, ok
qry.FindField('str_long').Asstring := '';   // IsNull becomes TRUE (wrong!)

the IsNull property on the LONG VARCHAR field returns TRUE even if it has been assigned a NOT NULL value (the empty string), while the short field behavior is correct.

(The property FormatOptions.StrsEmpty2Null for both the connection and the query is FALSE).

Furthermore, when I execute the Post() method, Delphi raises the exception on the LONG VARCHAR field:

Field 'str_long' must have a value

If I set 

qry.FindField('str_long').Required := FALSE;
qry.Post;

the record is successful inserted in the database, with empty strings values.

To make short a long story: if I insert a record with empty string values in a LONG VARCHAR field, the IsNull property returns a wrong value and I have to assign Required := False in order to get the INSERT operation executed.

In this small demonstrative application I try to insert

  • a record with NOT EMPTY strings (and everything works properly)

  • a record with EMPTY strings.

Test application output

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, FireDAC.Stan.Intf, FireDAC.Stan.Option, FireDAC.Stan.Error, FireDAC.UI.Intf, FireDAC.Phys.Intf,
  FireDAC.Stan.Def, FireDAC.Stan.Pool, FireDAC.Stan.Async, FireDAC.Phys, FireDAC.Phys.ASA, FireDAC.Phys.ASADef, FireDAC.VCLUI.Wait,
  FireDAC.Stan.Param, FireDAC.DatS, FireDAC.DApt.Intf, FireDAC.DApt, Data.DB, FireDAC.Comp.DataSet, FireDAC.Comp.Client, Vcl.StdCtrls,
  FireDAC.Phys.SQLite, FireDAC.Phys.SQLiteDef, FireDAC.Stan.ExprFuncs, FireDAC.Phys.ODBCBase, FireDAC.Comp.UI;

type
  TForm1 = class(TForm)
    conn: TFDConnection;
    qry: TFDQuery;
    memo: TMemo;
    procedure FormCreate(Sender: TObject);
  private
    procedure exec_insert(str_value : string);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

const
  LONG_FIELD = 'str_long';
  SHORT_FIELD = 'str_short';

procedure TForm1.exec_insert(str_value : string);

  procedure msg(s : string);
  begin
    memo.Text := memo.Text + s + #13#10
  end;

begin
  msg('======================');
  msg('INSERT VALUE = "' + str_value + '"');
  try
    qry.Insert;

    if qry.FindField(SHORT_FIELD).IsNull then msg('BEFORE assign SHORT field is NULL')
    else msg('BEFORE assign SHORT field is NOT NULL');
    if qry.FindField(LONG_FIELD).IsNull then msg('BEFORE assign LONG field is NULL')
    else msg('BEFORE assign LONG field is NOT NULL');
    msg('');

    qry.FindField(SHORT_FIELD).AsString := str_value;
    qry.FindField(LONG_FIELD).Asstring := str_value;

    if qry.FindField(SHORT_FIELD).IsNull then msg('AFTER assign SHORT field is NULL')
    else msg('AFTER assign SHORT field is NOT NULL');
    if qry.FindField(LONG_FIELD).IsNull then msg('AFTER assign LONG field is NULL')
    else msg('AFTER assign LONG field is NOT NULL');

    //qry.FindField(LONG_FIELD).Required := FALSE;
    qry.Post
  except
    on e: Exception do msg('EXCEPTION: ' + e.message)
  end;
  msg('')
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  s : string;
begin
  conn.params.Text := 'Database=jolly'#$D#$A'User_Name=jop'#$D#$A'Password=jpw'#$D#$A'Server=jolly'#$D#$A'DriverID=ASA'#$D#$A;
  conn.FormatOptions.StrsEmpty2Null := FALSE;
  conn.Connected := TRUE;

  qry.FormatOptions.StrsEmpty2Null := FALSE;
  qry.SQL.Text := 'select * from string_null';
  qry.UpdateOptions.RequestLive := TRUE;
  qry.Active := TRUE;

  exec_insert('ABC');
  exec_insert('')
end;

end.

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 299
  ClientWidth = 635
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  OnCreate = FormCreate
  DesignSize = (
    635
    299)
  PixelsPerInch = 96
  TextHeight = 13
  object memo: TMemo
    Left = 120
    Top = 8
    Width = 273
    Height = 283
    Anchors = [akLeft, akTop, akBottom]
    TabOrder = 0
  end
  object conn: TFDConnection
    Left = 28
    Top = 12
  end
  object qry: TFDQuery
    Connection = conn
    Left = 28
    Top = 64
  end
end

program Project1;

uses
  Vcl.Forms,
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

I have not tested the behavior with other databases.

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