Linq Query with dynamic type

Question

I am using the following linq to parse a dataset that I have returned:

 row.Field<long?>("id").HasValue == false &&

The problem I'm running into is that when the dataset is obtained from Sql Server, the field needs to be parsed with <int?> and when it's obtained from Oracle, it needs to be parsed as <long?>. Is there a way to create a variable that I can pass in to the .Field method to dynamically set this data type? I'd like to have something like this:

Type T = IsSqlServer ? typeof(int?) : typeof(long?);
....
row.Field<T>("id").HasValue == false &&

Thanks in advance!

Answer 1

You can use the dynamic keyword for just this purpose. See here for the programming guide.

I hope this helps.

Answer 2

You could either use reflection (not recommended) or just use the ternary operator:

!(IsSqlServer ? row.Field<int?>("id").HasValue : row.Field<long?>("id").HasValue)

Answer 3

Here's an extension method:

public static class DataRowHelpers
{
    private static readonly Dictionary<Type, MethodInfo> FieldSpecialized = new Dictionary<Type, MethodInfo>();

    public static bool FieldHasValue(this DataRow row, Type type, string column)
    {
        MethodInfo fieldSpecialized;

        if(!FieldSpecialized.TryGetValue(type, out fieldSpecialized))
        {       
            var extensions = typeof(DataRowExtensions);
            var fieldGeneric = extensions.GetMethod("Field",
                                                    new[] { typeof(DataRow), typeof(string) });
            fieldSpecialized = fieldGeneric.MakeGenericMethod(type);

            FieldSpecialized.Add(type, fieldSpecialized);
        }


        return fieldSpecialized.Invoke(null, new object[] { row, column }) != null;
    }
}

Usage:

var type = IsSqlServer ? typeof(int?) : typeof(long?);

var predicate = row.FieldHasValue(type, "id");