NpgsqlBatchCommand.ExecuteReader() & NpgsqlBatchCommand.Connection Gone?-CodePudding

I wanted to execute my reader for Npgsql query but there's an error stated like this:

'NpgsqlBatchCommand' does not contain a definition for 'Connection' and no accessible extension method 'Connection' accepting a first argument of type 'NpgsqlBatchCommand' could be found (are you missing a using directive or an assembly reference?) [Assembly-CSharp]

'NpgsqlBatchCommand' does not contain a definition for 'ExecuteReader' and no accessible extension method 'ExecuteReader' accepting a first argument of type 'NpgsqlBatchCommand' could be found (are you missing a using directive or an assembly reference?) [Assembly-CSharp]

Anyone knows why? Or does it have a new function or got deleted for version 6.0.5???

Here's my code:

using Npgsql;
        
        void Start()
        {
            using(NpgsqlConnection conn = new NpgsqlConnection())
            {
                conn.ConnectionString = "Server = localhost; Port = 5433; Database = 
            Postgres2; User Id = postgres; Password = admin";
                
                try
                {
                    NpgsqlBatchCommand cmd = new NpgsqlBatchCommand();
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = "SELECT id FROM m_pasukan";
                    cmd.Connection = conn;

                    conn.Open();

                    Debug.Log("Connection Open!");

                    NpgsqlBatchCommand sdr = cmd.ExecuteReader();

                    while(sdr.Read())
                    {
                        int id = (int)sdr["id"];
                        Debug.Log(id);
                    }
                }
                catch(Exception ex)
                {
                    Debug.Log("Cannot Open Connection!!");
                }
            }
        }

CodePudding user response：

They aren't gone. The wrong class is used. The code uses NpgsqlBatchCommand instead of NpgsqlCommand. The class that derives from ADO.NET's DbCommand base class and implements the IDbCommand interface is NpgsqlCommand, not NpgsqlBatchCommand.

Your code should be :

var cmd = new NpgsqlCommand();

or even :

using(var cmd=new NpgsqlCommand())
{
...
}

using(var cmd=new NpgsqlCommand(sql,conn))
{
...
}

ExecuteReader returns a DbDataReader that needs to be disposed too. A DbDataReader is a fast-forward cursor over the query results that consumes both client and server resources :

using(var sdr = cmd.ExecuteReader())
{
...
}

CodePudding user response：

If what you want is to execute a single SQL statement (SELECT id FROM m_pasukan), then you should indeed use NpgsqlCommand.

NpgsqlBatchCommand is part of a new ADO.NET batching API, which is an alternative to NpgsqlCommand for when you want to execute more than one command: here are the relevant Npgsql docs.

The problem with NpgsqlCommand in that scenario is that you include multiple statements separated by semicolons, forcing the database driver to parse SQL and split the statements out to different wire protocol messages.

To use the new batching API, create an NpgsqlBatch and add NpgsqlBatchCommands to it. Then, execute the NpgsqlBatch, not the NpgsqlBatchCommands.

await using var batch = new NpgsqlBatch(conn)
{
    BatchCommands =
    {
        new("INSERT INTO table (col1) VALUES ('foo')"),
        new("SELECT * FROM table")
    }
};

await using var reader = await cmd.ExecuteReaderAsync();

Extra reading: