Null value types using the positional parameter API - guidance about doc HOT 4 CLOSED

@erichiller at the moment, the last version is the only one that works: DBNull.Value is the way to represent a database null value.

This is an unfortunate situation which I hope to resolve, but it's important to think about all this in the context of the .NET data API (ADO.NET), and not just Npgsql. In the meantime, you can have an extension method which adds a non-generic parameter with DBNull.Value for a null value, and a generic one with the non-null value otherwise.

Thanks for the information. It might be good to have this in the official docs. I would be happy to add if you'd like.

from doc.

It seems you are conflating positional parameters (with no name) and the generic NpgsqlParameter<T>: you can (and should) use positional parameters with the non-generic NpgsqlParameter just fine.

The problem of passing null when using the generic NpgsqlParameter<T> with .NET value types is tracked by npgsql/npgsql#3679.

from doc.

Which non-generic variant should be used? I've tried:

new NpgsqlParameter { NpgsqlDbType           = NpgsqlDbType.Double, NpgsqlValue = nullableDouble } ;
// System.InvalidCastException: Parameter  must be set

new NpgsqlParameter { NpgsqlValue = nullableDouble } ; 
// System.InvalidOperationException: Parameter '$5' must have either its NpgsqlDbType or its DataTypeName or its Value set

new NpgsqlParameter { Value = nullableDouble } ; 
// System.InvalidOperationException: Parameter '$5' must have either its NpgsqlDbType or its DataTypeName or its Value set

new NpgsqlParameter( nullableDouble ) ;
// Cannot resolve constructor 'NpgsqlParameter(System.Nullable<double>)', candidates are...

/* The only one I've gotten to work */
nullableDouble is {} nonNullableDouble ? new NpgsqlParameter{ NpgsqlValue = nonNullableDouble, NpgsqlDbType = NpgsqlDbType.Double } : new NpgsqlParameter{ Value = DBNull.Value } ;

from doc.

@erichiller at the moment, the last version is the only one that works: DBNull.Value is the way to represent a database null value.

This is an unfortunate situation which I hope to resolve, but it's important to think about all this in the context of the .NET data API (ADO.NET), and not just Npgsql. In the meantime, you can have an extension method which adds a non-generic parameter with DBNull.Value for a null value, and a generic one with the non-null value otherwise.

from doc.