使用Delphi在已安装的应用程序中进行数据库版

重要的部分是：

Because dbisam doesn’t support views,
the version number is stored (along
with a bunch of other info) in an ini
file in the database directory.

I have a datamodule,
TdmodCheckDatabase. This has a
TdbisamTable component for every table
in the database. The table component
contains all fields in the table and
is updated whenever the table is
changed.

To make database changes,the
following process was used:

1. Increase the version number in the application
2. Make and test DB changes.
3. Update the affected tables in TdmodCheckDatabase
4. If necessary (rarely) add further upgrade queries to
   TdmodCheckDatabase. E.g. to set the
   values of new fields,or to add new
   data rows.
5. Generate a CreateDatabase unit script using the supplied database
   tools.
6. Update unit tests to suit the new db

When the application is run,it goes
through the following process

1. If no database is found,then run CreateDatabase unit and then do
   step 3
2. Get the current version number from the database ini file
3. If it is less than the expected version number then
   Run CreateDatabase (to create any new tables)
   Check every table component in TdmodCheckDatabase
   Apply any table changes
   run any manual upgrade scripts
4. Update the version number in the database ini file

代码示例是

class procedure TdmodCheckDatabase.UpgradeDatabase(databasePath: string; currentVersion,newVersion: integer);
var
module: TdmodCheckDatabase;
f: integer;
begin
module:= TdmodCheckDatabase.create(nil);
try
  module.OpenDatabase( databasePath );

  for f:= 0 to module.ComponentCount -1  do
  begin
    if module.Components[f] is TDBISAMTable then
    begin
      try
        // if we need to upgrade table to dbisam 4
        if currentVersion <= DB_VERSION_FOR_DBISAM4 then
          TDBISAMTable(module.Components[f]).UpgradeTable;

        module.UpgradeTable(TDBISAMTable(module.Components[f]));
      except
       // logging and error stuff removed
      end;
    end;
  end;

  for f:= currentVersion + 1 to newVersion do
    module.RunUpgradeScripts(f);

  module.sqlMakeIndexes.ExecSQL; // have to create additional indexes manually
 finally
  module.DBISAMDatabase1.Close;
  module.free;
end;
end;


procedure TdmodCheckDatabase.UpgradeTable(table: TDBISAMTable);
var
 fieldIndex: integer;
 needsRestructure: boolean;
 canonical: TField;
begin
 needsRestructure:= false;

 table.FieldDefs.Update;

 // add any new fields to the FieldDefs
 if table.FieldDefs.Count < table.FieldCount then
 begin
   for fieldIndex := table.FieldDefs.Count to table.Fields.Count -1 do
   begin
     table.FieldDefs.Add(fieldIndex + 1,table.Fields[fieldIndex].FieldName,table.Fields[fieldIndex].DataType,table.Fields[fieldIndex].Size,table.Fields[fieldIndex].Required);
   end;
   needsRestructure:= true;
 end;

 // make sure we have correct size for string fields
 for fieldIndex := 0 to table.FieldDefs.Count -1 do
 begin
   if (table.FieldDefs[fieldIndex].DataType = ftString) then
   begin
     canonical:= table.FindField(table.FieldDefs[fieldIndex].Name);
     if assigned(canonical) and (table.FieldDefs[fieldIndex].Size <> canonical.Size) then
   begin
     // field size has changed
     needsRestructure:= true;
     table.FieldDefs[fieldIndex].Size:= canonical.Size;
   end;
   end;
 end;

 if needsRestructure then
   table.AlterTable(); // upgrades table using the new FieldDef values
end;

procedure TdmodCheckDatabase.RunUpgradeScripts(newVersion: integer);
begin
 case newVersion of
   3: sqlVersion3.ExecSQL;
   9: sqlVersion9.ExecSQL;
   11: begin  // change to DBISAM 4
         sqlVersion11a.ExecSQL;
         sqlVersion11b.ExecSQL;
         sqlVersion11c.ExecSQL;
         sqlVersion11d.ExecSQL;
         sqlVersion11e.ExecSQL;
       end;
   19: sqlVersion19.ExecSQL;
   20: sqlVersion20.ExecSQL;
 end;
end;