Does a Generic Repository need a Base Entity class to be applied everywhere?

Question

I am creating an Intranet website with ASP.NET MVC and Onion Architecture. I have been implementing the repository pattern but I have a difficulty.

Answer 1

You're calling the Queryable.SingleOrDefault method.

Its second parameter has the type Expression<Func<T, bool>> so you can build expression manually, using as identifier property as you wish.

Short example:

public T Get(long id)
{
    var idName = "ID" + typeof(T).Name; // For Document would be IDDocument
    var parameter = Expression.Parameter(id.GetType());
    var property = Expression.Property(parameter, idName)
    var idValue = Expression.Constant(id, id.GetType());
    var equal = Expression.Equal(property, idValue);
    var predicate = Expression.Lambda<Func<T, bool>>(equal, parameter);
    return entities.SingleOrDefault(predicate);
}

Imagine you wrote lambda function (T obj) => obj.IdProperty == id. Here obj is parameter, and idName should store "IdProperty" string. property means obj.IdProperty, idValue means the value if id. equal means obj.IdProperty == id, and predicate means whole expression (T obj) => obj.IdProperty == id.