Reading Data

ADO.NET provides a basic object to read data from a database. This object is the DataReader, or CtreeSqlDataReader in the particular case of our data provider. CtreeSqlDataReader is a fast forward-only and read-only representation of the data returned by a c-treeACE SQL query. A DataReader object is obtained by calling the ExecuteReader() method of the CtreeSqlCommand object, after setting the CommandText property of a CtreeSqlCommand object to the appropriate c-treeACE SQL query.

You should always call the Close() method when you have finished using the CtreeSqlDataReader object.

The examples below show how to use a DataReader with various .NET languages.

.NET VB Example

Sub DisplayNames()

   Dim conString As String = “User=ADMIN;Password=ADMIN;Database=ctreeSQL”

   Dim hConnection As New CtreeSqlConnection(conString)

   Dim hCommand As New CtreeSqlCommand(hConnection)

   Dim reader As CtreeSqlDataReader

   hConnection.Open()

   hCommand.CommandText = “select name from tab1”

   reader = hCommand.ExecuteReader()

   While reader.Read()

      Console.WriteLine(reader[“name”])

   End While

   reader.Close()

   hConnection.Close()

End Sub

.NET C# Example

void DisplayNames()

{

   String conString = “User=ADMIN;Password=ADMIN;Database=ctreeSQL”;

   CtreeSqlConnection hConnection = new CtreeSqlConnection(conString);

   CtreeSqlCommand hCommand = new CtreeSqlCommand(hConnection);

   CtreeSqlDataReader reader;

   hConnection.Open();

   hCommand.CommandText = “select name from tab1”;

   reader = hCommand.ExecuteReader();

   while (reader.Read())

        Console.WriteLine(reader[“name”]);

   reader.Close();

   hConnection.Close();

}

.NET C++ Example

void CreateTable()

{

   String* conString = S“User=ADMIN;Password=ADMIN;Database=ctreeSQL”;

   CtreeSqlConnection* hConnection = new CtreeSqlConnection(conString);

   CtreeSqlCommand* hCommand = new CtreeSqlCommand(hConnection);

   CtreeSqlDataReader* reader;

   hConnection->Open();

   hCommand->CommandText = “select name from tab1”;

   reader = hCommand->ExecuteReader();

   while (reader->Read())

      Console::WriteLine(reader[“name”]);

   reader->Close();

   hConnection->Close();

}

.NET Delphi Example

procedure DisplayNames

var

   conString : String;

   hConnection : CtreeSqlConnection;

   hCommand : CtreeSqlCommand;

   reader : CtreeSqlDataReader;

begin

   conString := 'User=ADMIN;Password=ADMIN;Database=ctreeSQL';

   hConnection := CtreeSqlConnection.Create(conString);

   hCommand := CtreeSqlCommand(hConnection);

   hConnection.Open();

   hCommand.CommandText := 'select name from tab1';

   reader := hCommand.ExecuteReader();

   while reader.Read() do

      Console.WriteLine(reader['name']);

   reader.Close();

   hConnection.Close();   

end;