I'm using MVC and Entity Framework. I've created a class in my model folder with this code below. I keep getting the error message above with both queries below. I know there is a known issue on referencing non-scalar variables, but I'm not sure how to implement a workaround:
http://msdn.microsoft.com/en-us/library/bb896317.aspx#Y1442
private MovieLibraryDBEntities movieLibraryDBEntitiesContext;
public int getNumberOfEntriesReserved()
{
return (from m in movieLibraryDBEntitiesContext.Movies
where m.CheckedOut.Equals(1)
select m).Count();
//return movieLibraryDBEntitiesContext.Movies
// .Where(e => e.CheckedOut.Equals(1))
// .Select (e => e.Title).Count();
}
You cannot use m.CheckedOut.Equals(1) in linq-to-entities query. Use m.CheckedOut == 1 but CheckedOut must be integer.
This is an older question. I had the same problem when trying to filter a nullable column using the IQueryable interface. I solved the problem by first checking to see if the object had a value and then checking the value.
widgets = widgets.Where(x => x.ID.HasValue.Equals(true) && x.ID.Value.Equals(widgetID));
same issue using Any()
i had to change my where clause to search on primitive types, for me int
so this
where order.User == user
becomes this
where order.User.UserId == user.UserId
There is a blog post explaining the quirk.
Related
I have simplified the following example from my code and hoping there's no obvious compilation errors because of it. Lets say I have the following entities (not what i actually have, please assume I have no EF or schema issues, this is just for example):
public class Company
{
public string GroupProperty {get;set;}
public virtual ICollection<PricingForm> PricingForms {get;set;}
}
public class PricingForm
{
public decimal Cost {get;set;}
}
And I want to query like so:
IQueryable DynamicGrouping<T>(IQueryable<T> query)
{
Expression<Func<Company, decimal?>> exp = c => c.PricingForms.Sum(fr => fr.Cost);
string selector = "new (it.Key as Key, #0(it) as Value)";
IQueryable grouping = query.GroupBy("it.GroupProperty", "it").Select(selector, exp);
return grouping;
}
I get the following error when calling the groupby/select line:
System.Linq.Dynamic.ParseException: 'Argument list incompatible with lambda expression'
What type is "it" when grouped? I have tried using other expressions that assume it is an IGrouping<string, Company>, or a IQueryable<Company>, same error. I've tried just selecting "Cost" and moving the Sum() aggregate into the selector string (i.e. Sum(#0(it)) as Value) and always seem to get the same error.
I eventually tried something along the lines of:
Expression<Func<IEnumerable<Company>, decimal?>> exp = l => l.SelectMany(c => c.PricingForms).Sum(fr => fr.Cost);
However this one, I get farther but when attempting to iterate through the results I got a different error.
The LINQ expression node type 'Invoke' is not supported in LINQ to Entities.
So, with this dynamic grouping and injecting my own select expression, what should I assume the datatype of 'it' is? Will this even work?
The type of it is IGrouping<TKey, TElement>, where TKey is dynamic based on the keySelector result type, and TElement is the element type of the input IQueryable. Luckily IGrouping<TKey, TElement> inherits (is a) IEnumerable<TElement>, so as soon as you know the input element type, you can safely base selector on IEnumerable<TElement>.
In other words, the last attempt based on Expression<Func<IEnumerable<Company>, decimal?>> is correct.
The new error you are getting is because #0(it) generates Expression.Invoke call which is not supported by EF. The easiest way to fix that is to use LINQKit Expand method:
Expression<Func<Company, decimal?>> exp = c => c.PricingForms.Sum(fr => fr.Cost);
string selector = "new (it.Key as Key, #0(it) as Value)";
IQueryable grouping = query.GroupBy("it.GroupProperty", "it").Select(selector, exp);
// This would fix the EF invocation expression error
grouping = grouping.Provider.CreateQuery(grouping.Expression.Expand());
return grouping;
var dic = context.Treasure.Include("TreasureShare")
.Where(t => t.TreasureShare.IsShared && t.TreasureShare.EvaluationContent.Contains(keyword))
.ToDictionary(t => t.ProductUrl, t => t.ProductId, EqualityComparer<string>.Default);
I got an error:
An item with the same key has already been added.
So why the equalitycomparer not work, and how to use a equalitycomparer to get different records while querying to database.
Updated:
I know IEqualityComparer can only be executed locally, but I didn't get an error like:
LINQ to Entities does not recognize the method 'System.Linq.IQueryable1[Panli.Service.Share.DataAccess.DbData.Treasure] Distinct[Treasure](System.Linq.IQueryable1[Panli.Service.Share.DataAccess.DbData.Treasure], System.Collections.Generic.IEqualityComparer`1[Panli.Service.Share.DataAccess.DbData.Treasure])' method, and this method cannot be translated into a store expression.
except I change the codes to below:
dic = context.Treasure.Include("TreasureShare")
.Where(t => t.TreasureShare.IsShared && t.TreasureShare.EvaluationContent.Contains(theme))
.Distinct(new TreasureEqualityComparer()).ToDictionary(t => t.ProductUrl, t => t.ProductId);
This is my TreasureEqualityComparer:
public class TreasureEqualityComparer : EqualityComparer<Treasure>
{
public override bool Equals(Treasure x, Treasure y)
{
return x.ProductUrl.ToLower() == y.ProductUrl.ToLower();
}
public override int GetHashCode(Treasure obj)
{
return obj.ProductUrl.ToLower().GetHashCode();
}
}
So why not throw an exception just like the Distinct() when I use ToDictionary(..) which has an IEqualityComparer param ? Anyone can explain this ?
So why not throw an exception?
The ToDictionary part is executed in memory. This is apparent when you investigate the SQL that is executed: nothing that shows any preparation for a conversion to Dictionary.
The query expression with Distinct on the other hand is translated into SQL as a whole (except it isn't because it fails). EF tries to let the database do the hard work of returning distinct values, but of course a comparer can't be translated into SQL, so this overload of Distinct() is not supported.
As for the duplicate key: apparently there are duplicate URL's (ignoring case). Maybe you should use group by.
Dictionary key has to be unique. In this case you are using ProductUrl as dictionary key and ProductId as value, unfortunately as the error indicated there are more then one records in Table having same ProductUrl. So you can't use it as a dictionary key.
Given an EntityObject, I'd like an object-oriented way find all related items as part of my data-source query.
The following produces the correct output, but brings all the rows over the wire to do it.
Parent. // EntityObject
Children. // EntityCollection
Where(o => o.Gender == 'm'). // IEnumerable (local!)
OrderBy(o => o.Age). // IOrderedEnumerable
Skip(pages * pageSize).Take(pageSize); // (Inefficient paging!)
I need to support a UI with this (filter using other criteria, sort, and paginate before returning results over the wire). I reordered to leverage Queryable:
Repository. // Repository
Children. // ObjectSet
Where(o => o.Parent == Parent && o.Gender == 'm'). // ObjectQuery, runtime error
OrderBy(o => o.Age). // IOrderedQueryable
Skip(pages * pageSize).Take(pageSize);
but this yields the error:
Unable to create a constant value of type 'DataModel.Parent'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
Is there a natural, object-oriented way to query on this relation, using Linq to Entities? Or do I necessarily fall-back to SQL for this?
I thought for a moment that CreateSourceQuery was going to be the answer, but it can't be applied to an EntityObject.
I can't do a test for what I'm saying, but I think that you get the error because EF doesn't know how to translate o.Parent == Parent into a SQL statement. Try compare the Ids of the two parents..
o.Parent.Id == Parent.Id
To select all Schedulings which are active, I have the following code:
var allSchedulesOnALine = CurrentUser.Lines.SelectMany(o => o.Scheduling).Where(o => o.Active);
var allSchedulesUnscheduled = Entities.SchedulingSet
.Where(o => o.Line == null && o.Site.Id == CurrentUser.Site.Id &&
o.Factory == CurrentUser.Factory && o.Active);
IEnumerable<Scheduling> allSchedules = allSchedulesUnscheduled.Union(allSchedulesOnALine);
foreach(Scheduling schedule in allSchedules.OrderBy(o => o.Ordering))
{
//Do Stuff
}
(Factory is an int)
When I run this code, I get this cryptic error on the foreach line:
Unable to create a constant value of type 'System.Collections.Generic.IEnumerable`1'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
Strangely enough, I can enumerate both allSchedulesOnALine and allSchedulesUnscheduled separately. Even stranger, if I reorder the union:
IEnumerable<Scheduling> allSchedules = allSchedulesOnALine.Union(allSchedulesUnscheduled);
It works fine!
Does anyone have any idea why this would happen? Am I missing something crucial, or is this a bug?
I should mention I am using Entity Framework 3.5. EF4 is not an option for us currently - it is beyond my control :\
You're calling two different methods with your "reordering".
You don't show the types of allSchedulesOnALine or allSchedulesUnscheduled, but I'm betting allSchedulesOnALine is of type IEnumerable<Schedule> and allSchedulesUnscheduled is of type IQueryable<Schedule>.
So when you call Queryable.Union, you're asking the EF to translate the expression into SQL. But the argument you pass is of type IEnumerable<Schedule>, and it can't translate that into a query.
On the other hand, when you call Enumerable.Union, you're asking LINQ to Objects to do the whole thing in memory, which works fine, albeit perhaps slower.
So the reason the behavior is different is that you're calling two completely different methods, which do different things, but happen to have the same name. No, it's not a bug.
I have a situation where I'm trying to filter a LINQ select using a derived sub class.
ctx.BaseEntity.OfType<SubClass>() - this works fine.
However I'd like to do this using a string value instead. I've come across a performance barrier when I have lots (>20) Sub Classes and selecting an Entity without using OfType just isn't an option. I have a generic UI that renders from the base class, so I don't know what Class Type will be returned at compile time.
So what I'd like to do is this:
Perform a projected Select where I
return just the SubClassType from
the database
Perform a second select
using this value as the OfType to
only select the relevant related
entity from the database (No mass
unions generated)
int id = 1;
var classType = (from c in ctx.BaseClass.Include("ClassType")
where c.id == id
select new
{
c.ClassType.TypeName
}).First();
BaseClass caseQuery = ctx.BaseClass.OfType<classType.TypeName>()
.Include("ClassType")
.Include("ChildEntity1")
.Include("ChildEntity2")
.Where(x => x.id== id);
But obviously this won't work because OfType requires a Type and not a string.
Any ideas on how I can achieve this?
Update:
As a side note to the original question, it turns out that the moment you project a query that uses a Navigation Property - it builds the monster SQL too, so I've ended up using a stored procedure to populate my ClassType entity from the BaseClass Id.
So I've just got it to work using eSQL, which I'd never used before. I've posted the code here just in case it helps someone. Has anyone else got a more strongly typed solution they can think of?
BaseClass caseQuery = ctx.BaseClass.CreateQuery<BaseClass>("SELECT VALUE c FROM OFTYPE(Entities.[BaseClass],namespace.[" + classType.TypeName + "]) as c")
.Include("ClassType")
.Include("ChildEntity1")
.Include("ChildEntity2")
.Where(x => x.id== id).FirstOrDefault();
To answer the headline question about calling OfType with a string / runtime type, you can do the following:
// Get the type, assuming the derived type is defined in the same assembly
// as the base class and you have the type name as a string
var typeToFilter = typeof(BaseClass)
.Assembly
.GetType("Namespace." + derivedTypeName);
// The use reflection to get the OfType method and call it directly
MethodInfo ofType = typeof(Queryable).GetMethod("OfType");
MethodInfo ofTypeGeneric = method.MakeGenericMethod(new Type[] { typeToFilter });
var result = (IQueryable<Equipment>)generic.Invoke(null, new object[] { equipment });
Combine this with your stored procedure to get the class name and you (should?) avoid the massive join - I don't have table-per-type implementation to play with so I can't test.