Problem with TField data type.
lazarus / 63-Database

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MakorDal · 2016-01-14 05:42

I have some problem defining the fields of a TmemDataset. I want to
use a memDataset with some files to keep and manipulate the data for a
small personal project.

here are the code snipet I use to create the fields :

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
createField(fieldName, fieldLabel : String ; fieldType : TFieldType; 
                   group : Integer) : TField;begin  Result :=
TField.Create(nil);  Result.FieldName := fieldName; 
Result.SetFieldType(fieldType);  Result.FieldKind := fkData;  if
fieldLabel = '' then    Result.DisplayLabel := fieldName  else   
Result.DisplayLabel := fieldLabel;  result.DataSet := memDataset;  
Result.Tag:= group; end;    The call is quite simple :

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
createField('FIELDNAME', 'FieldDisplay', ftInteger, 2);Unfortunately,
this does not properly set the field type and compromise the whole
data editing afterwards. I get a ftUnknown field type. How can I set
the proper type for my fields ?

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balazsszekely · 2016-01-14 10:25

Try this:
1. Add memds, db to the uses clauses
2. Drop a TMemDataSet, TMemo and a TButton to your form
3. Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);var  I, Counter: Integer;begin 
with MemDataset1 do  begin    //create fields    FieldDefs.Clear;   
FieldDefs.Add('FirstName', ftString, 16, False);   
FieldDefs.Add('LastName', ftString, 16, False);   
FieldDefs.Add('BirthDate', ftDateTime, 0, False);    CreateTable;   
Open;     //add data    Append;    FieldByName('FirstName').AsString
:= 'John';    FieldByName('LastName').AsString := 'Smith';   
FieldByName('BirthDate').AsDateTime := EncodeDate(1994, 12, 14);   
Post;     Append;    FieldByName('FirstName').AsString := 'Free';   
FieldByName('LastName').AsString := 'Pascal';   
FieldByName('BirthDate').AsDateTime := EncodeDate(1970, 06, 21);   
Post;     //display data    First;    Counter := 0;    Memo1.Clear;  
while not EOF do    begin      Inc(Counter);      for I := 0 to
Fields.Count - 1 do      begin       // if Fields[I].FieldDef.DataType
 = ftDateTime then        if Fields[I].DataType  = ftDateTime then   
     Memo1.Lines.Add(Fields[I].FieldName + ' : ' +
FormatDateTime('YYYY.MM.DD', Fields[I].AsDateTime))        else      
  Memo1.Lines.Add(Fields[I].FieldName + ' : ' + Fields[I].AsString); 
   end;      Memo1.Lines.Add('');      Next;    end;    Close; 
end;end;
PS: Edited, see @howardpc's suggestion.

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howardpc · 2016-01-14 11:00

minor glitch (at least with Laz 1.4.4) - line 37 should be
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i if
Fields[I].DataType  = ftDateTime then

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balazsszekely · 2016-01-14 11:11

Quote@howardpc
minor glitch (at least with Laz 1.4.4) - line 37 should be:
    if Fields.DataType  = ftDateTime then Thank you Howard! I edited
my post.

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MakorDal · 2016-01-14 16:43

Thanks...
Except your solution allows me neither to set a field display name - I
found a workaround - nor a tag, which is quite important to my
project.

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howardpc · 2016-01-14 19:18

You could devise a routine of this sort:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses
db; procedure AddField(aDSet: TDataSet; const aFName, aFLabel:
string;  aFType: TFieldType; aSize, aGroup: integer; aRequired:
boolean=False);var  fld: TField;  fldDef: TFieldDef;begin 
aDSet.Close;  fldDef:=aDSet.FieldDefs.AddFieldDef;  with fldDef do
begin    Name:=aFName;    if (aFLabel = '') then     
DisplayName:=aFName    else      DisplayName:=aFLabel;   
DataType:=aFType;    Size:=aSize;    Required:=aRequired;  end; 
fld:=fldDef.CreateField(aDSet);  fld.Tag:=aGroup; 
aDSet.FieldDefs.Update;end; 
which you might call thus:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
AddField(MemDataset1, 'Extra', 'Extra Field', ftString, 30, 99);

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MakorDal · 2016-01-15 17:52

Thanks, this works !
I had decided not to use fielddef at first because it did not support
two memDataSet with similar field name. I had error message saying
that "a field with this name already exists"