I have custom OrderBy implementation, it only works for types without inheritance, if I want order by field from base type I got The LINQ expression could not be translated
public static IOrderedQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty, bool desc)
{
if (source == null)
{
throw new ArgumentNullException(nameof(source));
}
if (string.IsNullOrEmpty(orderByProperty))
{
throw new ArgumentNullException(nameof(orderByProperty));
}
var command = desc ? "OrderByDescending" : "OrderBy";
var type = typeof(TEntity);
var param = Expression.Parameter(type, "p");
var property = type.GetProperty(orderByProperty);
var propertyAccess = Expression.MakeMemberAccess(param, property);
var orderByExpression = Expression.Lambda(propertyAccess, param);
var resultExpression = Expression.Call(
typeof(Queryable),
command,
new Type[] { type, property.PropertyType },
source.Expression,
Expression.Quote(orderByExpression));
return (IOrderedQueryable<TEntity>)source.Provider.CreateQuery(resultExpression);
}
I am using entityframework core 2.2 but the very interesting thigs is that if I write just source.OrderBy(x=>x.someBaseField)
then it works without any problem, so there must by something with my custom implementation
In error log I got also the translated query and it looks like this, intereresting is end part
orderby new SomeType() {NewField = [entity].DbField, Id = [entity].Id}.Id desc
orderByExpression.Body {p => p.Id}
resultExpression
.Call System.Linq.Queryable.OrderByDescending(
.Call System.Linq.Queryable.Select(
.Call System.Linq.Queryable.Where(
.Call System.Linq.Queryable.Where(
.Constant<Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MyTypeView]>(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MyTypeView]),
'(.Lambda #Lambda1<System.Func`2[MyTypeView,System.Boolean]>)),
'(.Lambda #Lambda2<System.Func`2[MyTypeView,System.Boolean]>)),
'(.Lambda #Lambda3<System.Func`2[MyTypeView, MyTypeResult]>))
,
'(.Lambda #Lambda4<System.Func`2[MyTypeResult,System.Guid]>))
I've seen something like this before. The only difference between compiler generated and manual expression is the ReflectedType
property of the PropertyInfo
- in compiler generated code it's the same as DeclaringType
, which in this case is the base class, while in the PropertyInfo
obtained via type.GetProperty
it is the derived type used to obtain it.
For some unknown reason (probably a bug) this is confusing EF Core. The workaround is to change the code as follows:
var property = type.GetProperty(orderByProperty);
if (property.DeclaringType != property.ReflectedType)
property = property.DeclaringType.GetProperty(property.Name);
or use a helper method like this
static PropertyInfo GetProperty(Type type, string name)
{
for (; type != null; type = type.BaseType)
{
var property = type.GetProperty(name, BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly);
if (property != null) return property;
}
return null;
}
In order to support nested properties, I would add the following helpers
static Expression Property(Expression target, string name) =>
name.Split('.').Aggregate(target, SimpleProperty);
static Expression SimpleProperty(Expression target, string name) =>
Expression.MakeMemberAccess(target, GetProperty(target.Type, name));
and then use
var propertyAccess = Property(param, orderByProperty);
and
new Type[] { type, orderByExpression.ReturnType },
inside the method in question.