Changin default value of a paradox field

Hi All,

I've created one field which has a default value 100 (this default value is assigned using database desktop utility), I want to have a delphi piece of code using which I can change the default value of any database field to any user defined value.

Thanks in advance

Rammohan
splramAsked:
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kretzschmarConnect With a Mentor Commented:
ahh,

thats, why i wrote
//a validate check may not exist
:-))

but its now about ~3 years ago,
i wrote this based on a bdeapi-sample from borland,
and i guess i had searched some time
to get the cause on the opType for your reported failure

well glad you got it work

meikl ;-)
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kretzschmarCommented:
have one piece . . . searching
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kretzschmarCommented:
here it comes,

bde-unit is used in the unit-clause

from my paqs, modified dbiapi-samples

---------- Validation

For setting a validation-check in paradox

//Set a Valcheck, valcheck may not exist
procedure SetValCheck(Tbl: TTable; Field: TField; MinVal, MaxVal,
          DefVal: Pointer; MinSize,MaxSize,DefSize : Integer; Required: Bool);
var
 hDb: hDbiDb;
 TblDesc: CRTblDesc;
 VChk: pVChkDesc;
 Dir: String;
 NumVChks: Word;
 OpType: CROpType;

begin
 NumVChks := 0;
 SetLength(Dir, dbiMaxNameLen + 1);
 Check(DbiGetDirectory(Tbl.DBHandle, False, PChar(Dir)));
 SetLength(Dir, StrLen(PChar(Dir)));
 VChk := AllocMem(sizeof(VChkDesc));
 try
   FillChar(TblDesc, sizeof(CRTblDesc), #0);

   VChk.iFldNum := Field.Index + 1;
   Tbl.DisableControls;
   Tbl.Close;
   Check(DbiOpenDatabase(nil, nil, dbiReadWrite, dbiOpenExcl,
              nil, 0, nil, nil, hDb));
   Check(DbiSetDirectory(hDb, PChar(Dir)));
   with VChk^ do
   begin
     bRequired := Required;
     if MinVal <> nil then
     begin
       Inc(NumVChks);
       bHasMinVal := True;
       move(MinVal^, aMinVal, MinSize);
     end
     else
       bHasMinVal := False;
     if MaxVal <> nil then

     begin
       Inc(NumVChks);
       bHasMaxVal := True;
       move(MaxVal^, aMaxVal, MaxSize);
     end
     else
       bHasMaxVal := False;
     if DefVal <> nil then
     begin
       Inc(NumVChks);
       bHasDefVal := True;
       move(DefVal^, aDefVal, DefSize);
     end
     else
       bHasDefVal := False;

   end;
   TblDesc.iValChkCount := NumVChks;
   TblDesc.pVChkDesc := VChk;
   OpType := crADD;
   TblDesc.pecrValChkOp := @OpType;

   StrPCopy(TblDesc.szTblName, Tbl.TableName);
   StrCopy(TblDesc.szTblType, szParadox);
   Check(DbiDoRestructure(hDb, 1, @TblDesc, nil, nil, nil, False));
 finally
   Check(DbiCloseDatabase(hDb));
   FreeMem(VChk, sizeof(VChkDesc));
   Tbl.EnableControls;
   Tbl.Open;
 end;
end;

//Help Function to encode bde-date
Function GetBDEDate(Month, Day : Word; Year : SmallInt; var MyDate : DbiDate) : DbiDate;
begin
 Check(DbiDateEncode(Month, Day, Year, MyDate));
 Result := Mydate;
end;


//Table must be opened exclusive,
//a validate check may not exist
procedure TForm1.Button2Click(Sender: TObject);
var
 cmin,cmax,cdef : Double;
 lmin,lmax,ldef : Longint;
 amin,amax,adef : String;
 bdef : Boolean;
 dmin,dmax,ddef : dbiDate;
begin
 //Set validate for numeric Field
 cmin := -2.5;
 cmax := 2.5;
 cdef := 0.01;
 SetValCheck(Table6,Table6.FieldByName('Numeric'),@cmin,@cmax,@cdef,
             SizeOf(cMin),SizeOf(cMax),SizeOf(cdef),True);

 //Set Validate for Integer Field
 lmin := -100;
 lmax := 100;
 ldef := 1;
 SetValCheck(Table6,Table6.FieldByName('Integer'),@lmin,@lmax,@ldef,
             SizeOf(lMin),SizeOf(lMax),SizeOf(ldef),True);

 //Set Validate for Alphanumeric Field
 amin := 'A';
 amax := 'ABCDE';
 adef := 'AB';
 SetValCheck(Table6,Table6.FieldByName('Alpha'),@amin[1],@amax[1],@adef[1],
             length(amin),length(aMax),length(adef),True);

 //Set Validate for Boolean Field (Default only)
 bdef := False;
 SetValCheck(Table6,Table6.FieldByName('Boolean'),Nil,nil,@bdef,
             0,0,SizeOf(bdef),True);

 //Set Validate for DateField
 dMin := GetBDEDate(1,1,1999,dmin);
 dMax := GetBDEDate(12,31,1999,dmax);
 dDef := GetBDEDate(7,1,1999,ddef);
 SetValCheck(Table6,Table6.FieldByName('Date'),@dmin,@dmax,@ddef,
             SizeOf(dMin),SizeOf(dMax),SizeOf(ddef),True);
end;


-- hope this helps

meikl ;-)
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kretzschmarCommented:
appendix

if you want only set defaults,
them set the min and max-value to nil
like in the boolean sample above

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splramAuthor Commented:
Thanks for your prompt/early reply, I'm getting an error message when trying to change the default value for a string field the error is:

"INVALID ARRAY OF VALIDITY CHECK DESCRIPTORS".

This is how I'm invoking the SetValCheckFunction

amin := 'A';
amax := 'ABCDE';
adef := 'AB';
SetValCheck(Table1,Table1.FieldByName('Funcloc'),nil,nil,@adef[1],
            0,0,length(adef),True);


Whats wrong with this?

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kretzschmarCommented:
which delphi-version do you use?
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kretzschmarCommented:
just to say the sample was for d3 long time ago,

it could be that in later versions this conversion
,@adef[1], did not work.

replace it with

PChar(adef)

well, testing myself this evening (with d5)
(no delphi on hand yet)

meikl ;-)

           
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splramAuthor Commented:
Though I changed it to pchar(adef) its giving the same error, FYI, I'm working with delphi 5

the statement where error is cropping is:

  Check(DbiDoRestructure(hDb, 1, @TblDesc, nil, nil, nil, False));
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kretzschmarCommented:
well,
checking myself this evening (d5 i can check :-)
thats in ~5 hours

meikl ;-)
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splramAuthor Commented:
I think you have taken Me to the 1 step behind the solution, I would owe My sincere thanks if you can take Me to the complete solution.

Thanks a lot for your contrinution, hope I get answer after 5 hrs.

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kretzschmarCommented:
i will do my best for reproducing and solving
we will see, what happened :-))
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splramAuthor Commented:
Hello meikl,

Kudos to you, I cracked the error the problem was:

OpType was crAdd,
I changed it to
crMODIFY;

Then worked thanks a ton

bye
Rammohan
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kretzschmarCommented:
ahh,

thats, why i wrote
//a validate check may not exist
:-))

but its now about ~3 years ago,
i wrote this based on a bdeapi-sample from borland,
and i guess i had searched some time
to get the cause on the opType for your reported failure

well glad you got it work

meikl ;-)
0
 
kretzschmarCommented:
oops, doublepost, sorry :-))
0
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