Repository generic method GetById using eager loading

Question

I am using Entity Framework and would like to create generic GetById method in Repository class with eager loading:

Here is my method which uses lazy-lo

Answer 1

One possible way is to use FirstOrDefault with predicate over the DbSet with Includes. It's not hard to build manually a predicate using Expression.Equal method, but the main challenge is how to get the key property name. Luckily we can use some ObjectContext methods to do that, so the implementation could be like this (assuming we have access to the concrete DbContext instance):

public virtual TEntity GetById(object id, params string[] includeProperties)
{
    var propertyName = ((System.Data.Entity.Infrastructure.IObjectContextAdapter)DbContext).ObjectContext
        .CreateObjectSet().EntitySet.ElementType.KeyMembers.Single().Name;

    var parameter = Expression.Parameter(typeof(TEntity), "e");
    var predicate = Expression.Lambda>(
        Expression.Equal(
            Expression.PropertyOrField(parameter, propertyName),
            Expression.Constant(id)),
        parameter);

    var query = DbSet.AsQueryable();
    if (includeProperties != null && includeProperties.Length > 0)
        query = includeProperties.Aggregate(query, System.Data.Entity.QueryableExtensions.Include);
    return query.FirstOrDefault(predicate);
}