Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

restructering a table within a delphi program

Posted on 1997-12-27
3
Medium Priority
?
161 Views
Last Modified: 2010-04-04
Hi,

I need the following... I want to be able to add, remove, and edit fields (names, fieldsizes and fieldtypes) to a table in my program. I've tried using the tables fielddefs.add property and afterwards the createtable command. This works fine for adding fields, but this way existing date in the table is erased. I didn't find how I could remove a field from the table either.. Can anyone help me or at least point me in the right direction ?

Thanks
0
Comment
Question by:michaelsanders
3 Comments
 
LVL 1

Author Comment

by:michaelsanders
ID: 1354655
Adjusted points to 100
0
 
LVL 5

Expert Comment

by:ronit051397
ID: 1354656
0
 
LVL 1

Accepted Solution

by:
jackb022197 earned 300 total points
ID: 1354657
Here is a piece of code that adds a field to a specific table. You need to change the code to remove or change fields, but that works more or less in similar way:

This example will add a field to the end of an existing table.
NOTE: You must fill in all options in the ChangeRec with 0 or '' if the option is not used in the restructure. FillChar can be
used to do this: Fillchar(MyChangeRec, sizeof(MyChangeRec), 0);
This example uses the following input:
AddField(Table1, MyChangeRec);
ChangeRec is defind as follows:
ChangeRec = packed record
    szName: DBINAME;
    iType: byte;
    iSubType: byte;
    iLength: word;
    iPrecision: byte;
  end;
The function is defined as follows:
procedure AddField(Table: TTable; NewField: ChangeRec);
var
  Props: CURProps;
  hDb: hDBIDb;
  TableDesc: CRTblDesc;
  pFlds: pFLDDesc;
  pOp: pCROpType;
  B: byte;

begin
  // Make sure the table is open exclusively so we can get the db handle...
  if Table.Active = False then
    raise EDatabaseError.Create('Table must be opened to restructure');
  if Table.Exclusive = False then
    raise EDatabaseError.Create('Table must be opened exclusively to restructure');

  // Get the table properties to determine table type...
  Check(DbiGetCursorProps(Table.Handle, Props));
  pFlds := AllocMem((Table.FieldCount + 1) * sizeof(FLDDesc));
  FillChar(pFlds^, (Table.FieldCount + 1) * sizeof(FLDDesc), 0);
  Check(DbiGetFieldDescs(Table.handle, pFlds));

  for B := 1 to Table.FieldCount do begin
    pFlds^.iFldNum := B;
    Inc(pFlds, 1);
  end;
  try
    StrCopy(pFlds^.szName, NewField.szName);
    pFlds^.iFldType := NewField.iType;
    pFlds^.iSubType := NewField.iSubType;
    pFlds^.iUnits1  := NewField.iLength;
    pFlds^.iUnits2  := NewField.iPrecision;
    pFlds^.iFldNum  := Table.FieldCount + 1;
  finally
    Dec(pFlds, Table.FieldCount);
  end;

  pOp := AllocMem((Table.FieldCount + 1) * sizeof(CROpType));
  Inc(pOp, Table.FieldCount);
  pOp^ := crADD;
  Dec(pOp, Table.FieldCount);

  // Blank out the structure...
  FillChar(TableDesc, sizeof(TableDesc), 0);
  //  Get the database handle from the table's cursor handle...
  Check(DbiGetObjFromObj(hDBIObj(Table.Handle), objDATABASE, hDBIObj(hDb)));
  // Put the table name in the table descriptor...
  StrPCopy(TableDesc.szTblName, Table.TableName);
  // Put the table type in the table descriptor...
  StrPCopy(TableDesc.szTblType, Props.szTableType);
  // Close the table so the restructure can complete...
  TableDesc.iFldCount := Table.FieldCount + 1;
  Tabledesc.pfldDesc := pFlds;
  TableDesc.pecrFldOp := pOp;
  Table.Close;
  // Call DbiDoRestructure...
  try
    Check(DbiDoRestructure(hDb, 1, @TableDesc, nil, nil, nil, FALSE));
  finally
    FreeMem(pFlds);
    FreeMem(pOp);
    Table.Open;
  end;
end;
0

Featured Post

Vote for the Most Valuable Expert

It’s time to recognize experts that go above and beyond with helpful solutions and engagement on site. Choose from the top experts in the Hall of Fame or on the right rail of your favorite topic page. Look for the blue “Nominate” button on their profile to vote.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article explains how to create forms/units independent of other forms/units object names in a delphi project. Have you ever created a form for user input in a Delphi project and then had the need to have that same form in a other Delphi proj…
Introduction The parallel port is a very commonly known port, it was widely used to connect a printer to the PC, if you look at the back of your computer, for those who don't have newer computers, there will be a port with 25 pins and a small print…
We’ve all felt that sense of false security before—locking down external access to a database or component and feeling like we’ve done all we need to do to secure company data. But that feeling is fleeting. Attacks these days can happen in many w…
Is your data getting by on basic protection measures? In today’s climate of debilitating malware and ransomware—like WannaCry—that may not be enough. You need to establish more than basics, like a recovery plan that protects both data and endpoints.…
Suggested Courses
Course of the Month10 days, 22 hours left to enroll

886 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question