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reindex paradox table

D3, Paradox 7.0 and BDE 5.01

I am looking for some code to reindex a paradox table.

Thanx in advance,

Georg
please email to: gbc.des...@vip.{*word*104}city.dk

 

Re:reindex paradox table


On Fri, 04 Jun 1999 14:58:47 +0200, Georg Beyer Clausen

Quote
<gbc.des...@vip.{*word*104}city.dk> wrote:
>D3, Paradox 7.0 and BDE 5.01

>I am looking for some code to reindex a paradox table.

There are a number of ways you could approach this.

One way would be to make a call to the BDE API function DbiRegenIndexes.
This insulates you from having to know what indexes exist, if any, the BDE
handling all the code for you. Error checking can be handled by examining
the return value (type DBIResult) or by using the Check function (defined
in the BDE wrapper unit BDE).

  procedure TForm1.Button4Click(Sender: TObject);
  var
    aExclusive, aActive: Boolean;
  begin
    with Table1 Do Begin
      aActive := Active;
      Close;
      aExclusive := Exclusive;
      Exclusive := True;
      Open;
      Check(DbiRegenIndexes(Table1.Handle));
      Close;
      Exclusive := aExclusive;
      Active := aActive;
      Check(DbiSaveChanges(Table1.Handle));
    end;
  end;

As when calling any BDE API function, the BDE API wrapper unit BDE (for
Delphi 1, the units DbiTypes, DbiErrs, and DbiProcs) must be referenced in
the Uses section of the unit from which the call is to be made. The BDE API
function DbiSaveChanges, used here, forces any data changes in memory
buffer to be written to disk at that point.

Another way to handle this situation -- if you know at design-time all the
indexes that will exist for the table -- would be to iterate through the
items in the TIndexDefs object of the TTable component, delete each index
(DeleteIndex method), and then add all needed indexes back (AddIndex
method).

  procedure TForm1.Button3Click(Sender: TObject);
  var
    aName: String;
    i: Byte;
    aExclusive, aActive: Boolean;
  begin
    with Table1 do begin
      aActive := Active;
      Close;
      aExclusive := Exclusive;
      Exclusive := True;
      IndexDefs.Update;
      i := IndexDefs.Count;
      while i > 0 do begin
        aName := IndexDefs.Items[i - 1].Name;
        DeleteIndex(aName);
        Dec(i);
      end;
      AddIndex('', 'MainField', [ixPrimary]);
      AddIndex('Field1', 'Field1', []);
      AddIndex('Field2', 'Field2', []);
      IndexDefs.Update;
      Exclusive := aExclusive;
      Active := aActive;
      Check(DbiSaveChanges(Table1.Handle));
    end;
  end;

When iterating through the items in the TIndexDefs object, the cycling must
be backwards, from highest to lowest. This is to account for those table
types that have primary indexes. With those table types, deleting a primary
index first causes all secondary indexes to be unavailable, which
interferes with this iterating based on the TIndexDefs array object
contents. This is because a secondary index cannot exist in some table
types (such as Paradox) without an existing primary index. For the same
reason, when recreating the indexes, the process should start with the
primary index and then progress through all secondary indexes (if any are
to be created).

If information about the index definitions is not known at design-time,
this process becomes emminently more complex. The data from all indexes
will need to be saved to memory, the information for all indexes existing
simultaneously in memory. This is because a primary index would need to be
deleted at some point (to later be rebuilt), destroying references to any
secondary indexes (whether retrieval for the secondary indexes takes place
before or after deletion of the primary index). To accomplish this, some
multi-entity storage structure would need to be created to hold a variable
number of elements, one element per index. Each element would need to be
able to store the four bits of data that comprise an index's definition:
Name (String), Fields (String), Expression (String), and Options
(TIndexOptions). An array or a TList object of Pascal records with these
data fields would suffice for this purpose.

Once the definition information for all indexes are stored to memory, the
succeeding steps are similar to those for the previous method: Delete each
index (DeleteIndex) and then recreate each index based on the definition
information stored in the array or TList (AddIndex).

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