C# and PostgreSQL

Question

Can anyone show me a working example of using a cursor returned from PLSQL to C# code?

I found many examples showing how to fill a dataSet with returned data, but I cannot find how to use that cursor with a DataReader, so as a result I have {unnamed portal}.

NpgsqlTransaction tr = (NpgsqlTransaction) Connection.BeginTransaction();
NpgsqlCommand cursCmd = new NpgsqlCommand("someStoredProcedure(:inRadius)", (NpgsqlConnection) Connection);
cursCmd.Transaction = tr;
NpgsqlParameter rf = new NpgsqlParameter("ref", NpgsqlTypes.NpgsqlDbType.Refcursor);
rf.Direction = ParameterDirection.InputOutput;
cursCmd.Parameters.Add(rf);

I have to add this to use NpgsqlDataReader myReader; correctly:

tr.Commit();

When I wrote fetch after the sql command, it works but it is not suitable.

Solution 1

I have got some answers on my question.

Problem: I have a stored PLSQL procedure which returns refCursor. I have to get the returned data with a DataReader, but wwhen I added parameters, the db returned <unnamed portal>.

To walk through all returned data I have to write my code like so:

NpgsqlTransaction tr = (NpgsqlTransaction) Connection.BeginTransaction();
NpgsqlCommand cursCmd = new NpgsqlCommand("someStoredProcedure", (NpgsqlConnection) Connection);
cursCmd.Transaction = tr;
NpgsqlParameter rf = new NpgsqlParameter("ref", NpgsqlTypes.NpgsqlDbType.Refcursor);
rf.Direction = ParameterDirection.InputOutput;
cursCmd.Parameters.Add(rf);

NpgsqlParameter param2 = new NpgsqlParameter("param1", NpgsqlTypes.Int32);
rf.Direction = ParameterDirection.Input;
cursCmd.Parameters.Add(param2);
NpgsqlDataReader r = cmd.ExecuteReader();

while (r.Read())
{
    ; // r.GetValue(0);
}
r.NextResult();
while(r.Read())
{
    ;
}

tr.Commit();

Notice that you don't write your parameters in sql like func(:param1).

If you have parameters in your function, assign only the function name to the CommandText property and add parameters to the NpgsqlCommand.Parameters collection as usual. Npgsql will take care of binding your parameters correctly.

But now I have another problem. When I pass another output parameter to my CommandText, I have two fields in my result. One of them is 0{my first output param} and the other is <unnamed portal>.

In Oracle, I can directly convert a RefCursor parameter to a DataReader, but in postgresql, I cannot.

Solution 2

For your reference:

/// <summary>
/// Get data from the returning refcursor of postgresql function
/// </summary>
/// <param name="FunctionName">Function name of postgresql</param>
/// <param name="Parameters">parameters to pass to the postgresql function</param>
/// <param name="ErrorOccured">out bool parameter to check if it occured error</param>
/// <returns></returns>
public List<DataTable> GetRefCursorData(string FunctionName, List<object> Parameters, out bool ErrorOccured)
{ 
    string connectstring = ""; //your connectstring here
    List<DataTable >  dtRtn =new List<DataTable>();
    NpgsqlConnection connection = null;
    NpgsqlTransaction transaction = null;
    NpgsqlCommand command = null;            
    try
    {
        connection = new NpgsqlConnection(connectstring);
        transaction = connection.BeginTransaction();
        command = new NpgsqlCommand();
        command.Connection = connection;
        command.CommandType = CommandType.StoredProcedure;
        command.CommandText = FunctionName;
        command.Transaction = transaction;
        //
        if (Parameters != null)
        {
            foreach (object item in Parameters)
            {
                NpgsqlParameter parameter = new NpgsqlParameter();
                parameter.Direction = ParameterDirection.Input;
                parameter.Value = item;
                command.Parameters.Add(parameter);
            }
        }
        //
        NpgsqlDataReader dr = command.ExecuteReader();
        while (dr.Read())
        {
            DataTable dt = new DataTable();
            command = new NpgsqlCommand("FETCH ALL IN " + "\"" + dr[0].ToString() + "\"", Connection); //use plpgsql fetch command to get data back
            NpgsqlDataAdapter da = new NpgsqlDataAdapter(command);
            da.Fill(dt);
            dtRtn.Add(dt); //all the data will save in the List<DataTable> ,no matter the connection is closed or returned multiple refcursors
        }                
        ErrorOccured = false;
        transaction.Commit();
    }
    catch
    { 
        //error handling ...
        ErrorOccured = true;
        if (transaction != null) transaction.Rollback();
    }
    finally
    {
        if (connection != null) connection.Close();
    }
    return dtRtn;
}

Comments

[Yevhen]

I think it is rather specific question

[A-K]

This answer will be more useful when you provide a sample call of your function. For example, how should we initialize List<object> Parameters?

[AHMAD SUMRAIZ]

There is error "A command is already in progress:" on this line execution da.Fill(dt);