ADONetVCL > FAQ > General Questions

The list of general questions and answers.

Q1: Is there 'Getting Started Guide' (aka 'Quick Start Guide') for ADONetVCL?

A: First Steps to use ADONetVCL

Q2: What is the difference between trial and full versions?

A: ADO.Net VCL for Delphi Trial version:

•does not include the library source code files.

•30 days limitation period.

Q3: Does ADONetVCL supports a connection pooling?

A: Yes, it has. In general, connection pool minimizes the cost of repeatedly opening and closing connections. Connection pooling is handled differently for each of the data access components of the ADO.Net VCL for Delphi. When the connected property of the descendant of TDbConnection is set to True, the ADO.Net takes a "physical" connection from the pool and uses it. When the connected property of the descendant of TDbConnection is set to False, the "physical" connection is not closed, but put back into pool.

To use connection pooling in ADO.Net VCL, set the pooling property of the DAC Connection's Params property to True.

E.g. For SqlClientDAC, set the pooling to true like the code below:

TSqlClientConnection.Params.Pooling := True;

Q4: How to handle with Exceptions?

A: 1) Using SqlClientDAC:

Exported from Notepad++

uses
  CNClrLib.ADONet.SqlClient;

var
  msg: string;
begin
  try
//    ....Connect to Database and execute a query....
  except
    on E: Exception do
    begin
      if E is ESqlClientException then
      begin
        msg := 'Server:      ' + ESqlClientException(E).Errors[0].Server + #13#10 +
               'Line Number: ' + IntToStr(ESqlClientException(E).Errors[0].LineNumber) + #13#10 +
               'Number:      ' + IntToStr(ESqlClientException(E).Errors[0].Number) + #13#10 +
               'Message:     ' + ESqlClientException(E).Errors[0].Message;

        ShowMessage(msg);
      end
      else
        ShowMessage(E.Message);
    end;
  end;
end.

2) Using OdbcDAC:

Exported from Notepad++

uses
  CNClrLib.ADONet.Odbc;

begin
  try
//    ....Connect to Database and execute a query....
  except
    on E: Exception do
    begin
      if (E is EOdbcException) and (EOdbcException(E).ErrorCode = 335544472) then
        ShowMessage(strUserUnkown) // your Errormessage
      else
        ShowMessage(E.Message);
    end;
  end;
end.

Q5: Can I use the descendant of TOdbcQuery or any of other ADONet VCL Query components and connect it with a dataset provider and retieve the data in a Codegears' client dataset?

A: TOdbcQuery is the mix of the TOdbcDataReader, TOdbcDataAdapter, DataSet and few TOdbcCommand's. So, the TOdbcQuery has everythings inside to execute SQL command, send parameters data, receive and stored result sets, browse result sets, post changes back to a DB. There is no reason to use TOdbcQuery + DSP + CDS.

You can use TClrMemTable, TOdbcDataAdapter and TOdbcCommand directly, instead of TOdbcQuery. It gives more flexibility. But it also requires more coding.

TOdbcQuery is optimal "shortcut" for every day data application programming.

Note:

•Other ADONet VCL Query Components are TSqlClientQuery, TOracleClientQuery, TSQLiteQuery and TOleDbQuery.

•Other ADONet VCL DataReader Components are TSqlClientDataReader, TOracleClientDataReader, TSQLiteDataReader and TOleDbDataReader.

•Other ADONet VCL DataAdapter Components are TSqlClientDataAdapter, TOracleClientDataAdapter, TSQLiteDataAdapter and TOleDbDataAdapter.

•Other ADONet VCL Command Components are TSqlClientCommand, TOracleClientCommand, TSQLiteCommand and TOleDbCommand.

Q6: Is it necessary to create Index for ordering data?

A: You does not need to define Indexes, if you just need to order data. IndexFieldNames will work for you.

Q7: How to assign value to a ftGUID field?

A: Use the following code:


(AMemTable.FieldByName('Field1') as TGUIDField).AsGuid := aGUID;

Q8: How to specify a default value for a dataset field?

A: Assign an expression to the TField.DefaultExpression property.

Reference

•FAQ