Converting ESQL to LINQ to Entities. Sort by related entities - entity-framework

Question

I am using EF + RIA and unfortunately meet some problems with sorting by related entities.
For such purpose there is ESQL query that I implemented (found only this solution):
var queryESQL = string.Format(
#" select VALUE ent from SomeEntities as ent
join Attributes as ea ON ea.EntityId = ent.Id
where ea.AttributeTypeId = #typeId
order by ea.{0} {1}", columnName, descending ? "desc" : "asc");
var query = ObjectContext.CreateQuery<SomeEntity>(queryESQL, new ObjectParameter("typeId", attributeTypeId));
Tables have following structure:
<Attribute>:
int Id;
decimal DecimalColumn;
string StringColumn;
int EntityId;
int AttributeTypeId;
<SomeEntity>:
int Id;
string Name;
Is there any way to rewrite this stuff(sorting), using LINQ to Entities approach?

Answer 1

Here's my attempt, I can't guarantee it will work. I need to think more on how to get a dynamic column name, I'm not sure on that one. EDIT: you can use a string for the order column.
int typeId = 1115;
bool orderAscending = false;
string columnName = "StringColumn";
var query = from ent in SomeEntities
join ea in Attributes on ea.EntityId = ent.Id
where ea.AttributeTypeId = typeId;
if(orderAscending)
{
query = query.OrderBy(ea => columnName).Select(ea => ea.Value);
}
else
{
query = query.OrderByDescending(ea => columnName).Select(ea => ea.Value);
}
var results = query.ToList(); // call toList or enumerate to execute the query, since LINQ has deferred execution.
EDIT: I think that ordering after the select stops is from ordering by. I moved the select statement to after the order by. I also added the "query =", but I'm not sure if that is needed. I don't have a way to test this at the moment.
EDIT 3: I fired up LINQPad today and made a few tweaks to what I had before. I modeled your data in a Code-first approach to using EF and it should be close to what you have.
This approach works better if you're just trying to get a list of Attributes (which you aren't). To get around that I added an Entity property to the MyAttribute class.
This code works in LINQPAD.
void Main()
{
// add test entities as needed. I'm assuming you have an Attibutes collection on your Entity based on your tables.
List<MyEntity> SomeEntities = new List<MyEntity>();
MyEntity e1 = new MyEntity();
MyAttribute a1 = new MyAttribute(){ StringColumn="One", DecimalColumn=25.6M, Id=1, EntityId=1, AttributeTypeId = 1, Entity=e1 };
e1.Attributes.Add(a1);
e1.Id = 1;
e1.Name= "E1";
SomeEntities.Add(e1);
MyEntity e2 = new MyEntity();
MyAttribute a2 = new MyAttribute(){ StringColumn="Two", DecimalColumn=198.7M, Id=2, EntityId=2, AttributeTypeId = 1, Entity=e2 };
e2.Attributes.Add(a2);
e2.Id = 2;
e2.Name = "E2";
SomeEntities.Add(e2);
MyEntity e3 = new MyEntity();
MyAttribute a3 = new MyAttribute(){ StringColumn="Three", DecimalColumn=65.9M, Id=3, EntityId=3, AttributeTypeId = 1, Entity=e3 };
e3.Attributes.Add(a3);
e3.Id = 3;
e3.Name = "E3";
SomeEntities.Add(e3);
List<MyAttribute> attributes = new List<MyAttribute>();
attributes.Add(a1);
attributes.Add(a2);
attributes.Add(a3);
int typeId = 1;
bool orderAscending = true;
string columnName = "StringColumn";
var query = (from ent in SomeEntities
where ent.Attributes.Any(a => a.AttributeTypeId == typeId)
select ent.Attributes).SelectMany(a => a).AsQueryable();
query.Dump("Pre Ordering");
if(orderAscending)
{
// query = is needed
query = query.OrderBy(att => MyEntity.GetPropertyValue(att, columnName));
}
else
{
query = query.OrderByDescending(att => MyEntity.GetPropertyValue(att, columnName));
}
// returns a list of MyAttributes. If you need to get a list of attributes, add a MyEntity property to the MyAttribute class and populate it
var results = query.Select(att => att.Entity).ToList().Dump();
}
// Define other methods and classes here
}
class MyAttribute
{
public int Id { get; set; }
public decimal DecimalColumn { get; set; }
public string StringColumn { get; set; }
public int EntityId { get; set; }
public int AttributeTypeId { get; set; }
// having this property will require an Include in EF to return it then query, which is less effecient than the original ObjectQuery< for the question
public MyEntity Entity { get; set; }
}
class MyEntity
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<MyAttribute> Attributes { get; set; }
public MyEntity()
{
this.Attributes = new List<MyAttribute>();
}
// this could have been on any class, I stuck it here for ease of use in LINQPad
// caution reflection may be slow
public static object GetPropertyValue(object obj, string property)
{
// from Kjetil Watnedal on http://stackoverflow.com/questions/41244/dynamic-linq-orderby
System.Reflection.PropertyInfo propertyInfo=obj.GetType().GetProperty(property);
return propertyInfo.GetValue(obj, null);
}