TSQLDataDriverEh component

TSQLDataDriverEh is a universal DataDriver that can interact with server using SQL commands.

TSQLDataDriverEh have five objects of the TSQLCommandEh type: SelectCommand, DeleteCommand, InsertCommand, UpdateCommand, GetrecCommand.

Each object holds SQL expressions and parameters to execute command to get table data, delete record, insert record, update record and get one record. To execute commands TSQLDataDriverEh calls global event - DefaultSQLDataDriverResolver.OnExecuteCommand.

You should write this event to execute SQL expressions on the server and, if need, return DataSet to read data. When TSQLDataDriverEh is used as provider of data, it takes records from DataSet created in DefaultSQLDataDriverResolver.OnExecuteCommand event and writes them in TMemTableEh. On the measure of the requirement it takes given current record, writes them in TMemTableEh and goes over to following record.

When TSQLDataDriverEh is used as handler of changes, it takes a changed record from TMemTableEh, and call DefaultSQLDataDriverResolver.OnExecuteCommand event sending DeleteCommand, InsertCommand or UpdateCommand as a parameter.

Using TSQLDataDriverEh it is possible change a type of the access to data. Suffice it to rewrite global event - DefaultSQLDataDriverResolver.OnExecuteCommand.

TSQLDataDriverEh has a SpecParams property of TStrings type. You may use it to write the special values, which you can use in the DefaultSQLDataDriverResolver.OnExecuteCommand event. This event also is used by TServerSpecOperationsEh object when DefaultSQLDataDriverResolver.ServerSpecOperations property is assigned. List of special values depends of the type of TServerSpecOperationsEh object and values is filled similarly of description in the "Characteristic TXXXDataDriverEh.SpecParams" section.

DefaultSQLDataDriverResolver.ServerSpecOperations property has a TServerSpecOperationsEh type. This object is intended to process the special operations before or after ExecuteCommand procedure is performed. TServerSpecOperationsEh is a base class for classes
TOracleSpecOperationsEh, TMSSQLSpecOperationsEh, TInterbaseSpecOperationsEh, TInfromixSpecOperationsEh, TDB2SpecOperationsEh, TSybaseSpecOperationsEh and TMSAccessSpecOperationsEh.

Each Of these objects can process a SpecParams property in particular to get values of the autoincrement fields that is generated by the server.

On the name of the class it is possible to define a type of the server, for which class is intended.

For full functioning of TSQLDataDriverEh it is necessary to write DefaultSQLDataDriverResolver.OnExecuteCommand event to execute queries on the server and assign DefaultSQLDataDriverResolver.ServerSpecOperations property by the object that inherited from TServerSpecOperationsEh class. Assigning a ServerSpecOperations property makes sense, if you execute operations of the insertion in tables that have autoincrement field (or sequence objects).

The typical code to adjust working of TSQLDataDriverEh can be look as follows:

// Below code adjusts working of  TSQLDataDriverEh components in the whole Application to access 
// InderBase server via BDE Engine
uses … DataDriverEh, BDEDataDriverEh;
type
  TMainForm = class(TMainForm)
    Database1: TDatabase;
    SQLDataDriverEh: TSQLDataDriverEh;
…
procedure TMainForm.FormCreate(Sender: TObject);
begin
  DefaultSQLDataDriverResolver.OnExecuteCommand := OnExecuteSQLCommand;
  DefaultSQLDataDriverResolver.ServerSpecOperations := TInterbaseSpecOperationsEh.Create;
end;

procedure TMainForm.FormDestroy(Sender: TObject);
begin
  DefaultSQLDataDriverResolver.ServerSpecOperations.Free;
  DefaultSQLDataDriverResolver.ServerSpecOperations := Nil;
end;

function TMainForm.OnExecuteSQLCommand(SQLDataDriver: TCustomSQLDataDriverEh;
  Command: TCustomSQLCommandEh; var Cursor: TDataSet; var FreeOnEof,
  Processed: Boolean): Integer;
begin
  Result := DefaultExecuteBDECommandEh(SQLDataDriver, Command,
    Cursor, FreeOnEof, Processed, Database1.DatabaseName);
end;

TSQLDataDriverEh is a base class for TBDEDataDriverEh, TIBXDataDriverEh, TDBXDataDriverEh and TADODataDriverEh. These objects overwrite ExecuteCommand procedure and them can execute SQL expressions on the server and if need returns DataSet to read data. When SQL commands is called, it creates DataSet with type of corresponding type of the access to data. For TBDEDataDriverEh it is a TQuery, for TIBXDataDriverEh it is a TIBXQuery and so on. Furthermore, TBDEDataDriverEh, TIBXDataDriverEh, TDBXDataDriverEh can define TServerSpecOperationsEh object automatically. For TADODataDriverEh it is need to assign DefaultSQLDataDriverResolver. ServerSpecOperations because ADO technology does not allow to define a type of the server.

TSQLDataDriverEh have the next events: OnExecuteCommand write this event to execute SQL expression. You can call TCustomSQLDataDriverEh.DefaultExecuteCommand method to process this event by default. By default TCustomSQLDataDriverEh.DefaultExecuteCommand calls DefaultSQLDataDriverResolver.ExecuteCommand method, which, in turn, call DefaultSQLDataDriverResolver.OnExecuteCommand event.

OnGetBackUpdatedValues write this event to return updated values from server. You can call TCustomSQLDataDriverEh.DefaultGetUpdatedServerValues method to process action by default. TCustomSQLDataDriverEh.DefaultGetUpdatedServerValues call DefaultSQLDataDriverResolver.GetBackUpdatedValues. If it was not processed in DefaultSQLDataDriverResolver then it call InternalGetServerSpecOperations.GetBackUpdatedValues. InternalGetServerSpecOperations returns object of TServerSpecOperationsEh type.

Property TXXXDataDriverEh.SpecParams Property SpecParams kept a list of parameters and values. TXXXDataDriverEh use them when performing SQL expressions. Value of each parameter have to be wrote in the separate line in the format PARAMETER_NAME =VALUE. Depending on the type of the server (InterBase, Oracle, MSSQL, Informix) SpecParams can contain the following parameters.

On interaction with InterBase server:

GENERATOR - defines a name of the InterBase generator. DataDriver uses this parameter to get current value of generator after the insertion of new record.

GENERATOR_FIELD - defines a name of the field, which will be assigned current value of the generator after the insertion of new record.

AUTO_INCREMENT_FIELD - defines a name of the field, which DataDriver will set AutoIncremet type. It is used on making a structure of the internal array of record.

On interaction with Oracle server:

SEQUENCE - will assign a name of the field Oracle sequences. DataDriver uses this parameter for the reception of the current value of the sequence after the insertion of new record.

SEQUENCE_FIELD - will assign a name of the field, which will be assigned current value of the sequence after the insertion of new record.

AUTO_INCREMENT_FIELD - defines a name of the field, which DataDriver will set AutoIncremet type. It is used on making a structure of the internal array of record.

On interaction with MSSQL server:

AUTO_INCREMENT_FIELD - defines a name of the field, which DataDriver will set AutoIncremet type. It is used on making a structure of the internal array of record.

On interaction with Informix server:

AUTO_INCREMENT_FIELD - defines a name of the field, which DataDriver will set AutoIncremet type. It is used on making a structure of the internal array of record.

Example of the list of parameters for InterBase server:

   GENERATOR=EMP_NO_GEN
   GENERATOR_FIELD=emp_no
   AUTO_INCREMENT_FIELD=emp_no

SQL expression for the insertion of record must contain EMP_NO_GEN generator.

   insert into
     employee (EMP_NO, FIRST_NAME)
   values
     (:EMP_NO_GEN, :FIRST_NAME)