how can I get cursor data with calling stored procedure in npgsql

Question

I have looked into materials in www.npgsql.org, but couldn\'t find how to solve my problem...

Table, PostgreSQL

[City], [State]
\"Au         


        

Answer 1

With Shay's help, I figured out how we can fetch cursor in v3.x after removal of "dereferenced" feature. I think there are not much of good example on this, I hope this might help people save time to search example.

You can do this in npgsql ver3.x

1. CommandType.StoredProcedure (cursor name not defined)

conn.Open();
NpgsqlTransaction tran = conn.BeginTransaction();

NpgsqlCommand command = new NpgsqlCommand("show_cities", conn);
command.CommandType = CommandType.StoredProcedure;
command.ExecuteNonQuery();

command.CommandText = "fetch all in \"\"";
command.CommandType = CommandType.Text;

NpgsqlDataReader dr = command.ExecuteReader();
while (dr.Read())
{
    // do what you want with data, convert this to json or...
    Console.WriteLine(dr[0]);
}
dr.Close();

tran.Commit();
conn.Close();

2. CommandType.StoredProcedure (cursor name defined)

conn.Open();
NpgsqlTransaction tran = conn.BeginTransaction();

NpgsqlCommand command = new NpgsqlCommand("select show_cities(@ref)", conn);
command.CommandType = CommandType.Text;
NpgsqlParameter p = new NpgsqlParameter();
p.ParameterName = "@ref";
p.NpgsqlDbType = NpgsqlTypes.NpgsqlDbType.Refcursor;
p.Direction = ParameterDirection.InputOutput;
p.Value = "ref";
command.Parameters.Add(p);
command.ExecuteNonQuery();

command.CommandText = "fetch all in \"ref\"";
command.CommandType = CommandType.Text;

NpgsqlDataReader dr = command.ExecuteReader();
while (dr.Read())
{
    // do what you want with data, convert this to json or...
    Console.WriteLine(dr[0]);
}
dr.Close();

tran.Commit();
conn.Close();

3. CommandType.Text (cursor name defined)

conn.Open();
NpgsqlTransaction tran = conn.BeginTransaction();

NpgsqlCommand command = new NpgsqlCommand("select show_cities(@ref)", conn);
command.CommandType = CommandType.Text;
NpgsqlParameter p = new NpgsqlParameter();
p.ParameterName = "@ref";
p.NpgsqlDbType = NpgsqlTypes.NpgsqlDbType.Refcursor;
p.Direction = ParameterDirection.InputOutput;
p.Value = "ref";
command.Parameters.Add(p);
command.ExecuteNonQuery();

command.CommandText = "fetch all in \"ref\"";
command.CommandType = CommandType.Text;

NpgsqlDataReader dr = command.ExecuteReader();
while (dr.Read())
{
    // do what you want with data, convert this to json or...
    Console.WriteLine(dr[0]);
}
dr.Close();

tran.Commit();
conn.Close();

(reference for v2.x) http://www.sqlines.com/postgresql/npgsql_cs_result_sets

This is example for easy understanding, so if you want your function to return single result set, then instead of returning cursor, please consider it to return table as @Shay suggested or create a view not a function as @CeOnSql suggested.

Thanks !