Cheluis Cheluis - 3 months ago 40
C# Question

Retrieve serial ID with Npgsql when inserting with ExecuteScalar

I'm trying to insert a row into a PostgreSQL table with a serial primary key and I need to retrieve this column after it was inserted. I got something like this:

The table "pais" has 3 columns: id, pais, capital; id is a serial column and is its primary key.

NpgsqlCommand query = new NpgsqlCommand("insert into pais(nombre, capital) values(@nombre, @capital)", conn);
query.Parameters.Add(new NpgsqlParameter("nombre", NpgsqlDbType.Varchar));
query.Parameters.Add(new NpgsqlParameter("capital", NpgsqlDbType.Varchar));
query.Prepare();
query.Parameters[0].Value = this.textBox1.Text;
query.Parameters[1].Value = this.textBox2.Text;
Object res = query.ExecuteScalar();
Console.WriteLine(res);


It inserts the row on the table but "res" value is null. If I insert with the nexval('table_sequence') also returns null.

Any idea of how can I return the id of the table? Am I missing something?

Thanks in advance

Answer

In order to select the last identity inserted you need to use: currval(sequencename)

so your select statement should look like:

NpgsqlCommand query = new NpgsqlCommand("insert into pais(nombre, capital) values(@nombre, @capital);select currval('table_sequence');", conn);

You can find this and more at http://www.programmingado.net/a-117/Insert-data-and-retrieve-serial-autonumber-id.aspx

Cheers,

CEC

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