PostgreSQL, Get database exists with Npgsql

Question

I cant get reliable checking for database existence in NET/Npgsql at my program startup.

Here is code:

Public Function dbExists(ByVal _dbName As String) As Boolean

    Dim retval As Boolean = False
    Using mCon As New NpgsqlConnection(String.Format( _
                 "Server={0};Port={1};User Id={2};Password={3};", _
                  dbserver, dbport, "postgres", dbpass))
        Try
            mCon.Open()
            Using nCom = New NpgsqlCommand("SELECT 1 FROM pg_database WHERE datname='" + _dbName + "'", mCon)
                retval = CBool(nCom.ExecuteScalar())
            End Using
        Catch ex As Exception
            retval = False
        End Try
    End Using

    Return retval
End Function

This function return True no matter database exists or not. I also try with null checking on ExecuteScalar, getting Count(*) and all what I can without better result.

What to do to get it working?

phil_rawlings · Accepted Answer · 2013-11-17 15:36:34Z

8

Null checking on 'ExecuteScalar()' works for me (PostgreSQL 9.3 and Npgsql 2.0.12). Are you checking 'ExecuteScalar() == null'?

ExecuteScalar will return a .NET null not DBNull.Value (since it is not a record with a null value, it signifies no matching result).

I'm not a VB person but here's how I achieved it in C#:

bool dbExists;

using (NpgsqlConnection conn = new NpgsqlConnection("Server=127.0.0.1;Port=5432;Database=postgres;User Id=postgres;Password=testpass"))
{
    conn.Open();
    string cmdText = "SELECT 1 FROM pg_database WHERE datname='temp'";
    using (NpgsqlCommand cmd = new NpgsqlCommand(cmdText, conn))
    {
        dbExists = cmd.ExecuteScalar() != null;
    }
}

answered Nov 17, 2013 at 15:36

phil_rawlings

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1 Comment

Wine Too Over a year ago

Thanks Phil, I already finded a solution but your suggestion is useful too.

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