PostgreSQL, Get database exists with Npgsql - postgresql

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?

Answer 1

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;
}
}