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.
Related
I am currently working on a Database-Security-System, have to make sure that in the next two minutes of this database there is no other entry that equals to true. But somehow I always end up getting a System.NotSupportedException.
My Code
public IQueryable<AuthorizationAttempt> GetSuspiciousActivity(
DateTime from,
DateTime to)
{
return GetActivity(from, to).Where(e1 =>
e1.Result == false
&& !GetActivity(
e1.AttemptDate,
e1.AttemptDate.AddMinutes(2d)
).Any(e2 => e2.Result == true));
}
Error
System.NotSupportedException: "LINQ to Entities does not recognize the method 'System.DateTime AddMinutes(Double)' method, and this method cannot be translated into a store expression."
Thanks a lot
You can't use any helper methods inside your LINQ query. Use DbFunctions instead.
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;
I am receiviing this error when I try to delete rows using entity framework. Really do not understand why!
The object cannot be deleted because it was not found in the
ObjectStateManager.
public void Delete(int ticketID)
{
Modules.Entity.gmEntities context = new Modules.Entity.gmEntities();
var ticketitem = context.xticketitem.Select(p => p.TicketID == ticketID);
ticketitem.ToList().ForEach(r => context.DeleteObject(r));
context.SaveChanges();
}
By the call of context.xticketitem.Select(p => p.TicketID == ticketID); you will get a list of booleans that do not exist in context.
I think you should do something like this:
var ticketitem = context.xticketitem.Where(p => p.TicketID == ticketID);
ticketItem.ToList().ForEach(r => context.xticketitem.DeleteObject(r));
context.SaveChanges();
EDIT:
I've moved .ToList() on the next line to make differences between our snippets more evident. Let's try revise it step by step:
When you call var ticketitem = context.xticketitem.Select(p => p.TicketID == ticketID);
You are creating query that will go by all xticketitems and return whether each item's TicketID equals ticketID variable passed as an argument to your Delete method.
Result of this query is IEnumerable<bool>.
My code returns IEnumerable<xticketitem>. It's main difference.
When you call context.DeleteObject(r) your r variable is bool. and you are calling DeleteObject method on context. That mathod accepts parameter of type object (that's why you don't get error at compile time).
I'm calling DeleteObject on xticketitem ObjectSet that accepts strogly-typed parameter of xticketitem type.
Can I use an Expression Tree as an argument constraint in a FakeIteasy CallTo assertion?
Given a method on an interface with the following signature:
interface IRepository<TEntity>
{
TEntity Single(Expression<Func<TEntity, bool>> predicate);
Being called in code like so:
Flight flight = repository.Single(f => f.ID == id);
I have in mind a unit test doing something like this:
Expression<Func<Flight, bool>> myExpression = flight => flight.ID == 1;
A.CallTo(() => repository.Single(
A<Expression<Func<Flight, bool>>>.That.Matches(myExpression)))
.Returns(new Flight());
However this produces a warning: Try specifying type arguments explicitly.
I am currently having to use the Ignored property which is not ideal.
The "Matches"-method takes a lambda but you're trying to pass it the expression. What are you trying to say with the "Matches"-call? Are you matching on equality? In that case you'd just write:
A.CallTo(() => repository.Single(myExpression)).Returns(new Flight());
If you want to constrain the expression on something else you'd have to pass a predicate of the type: Func<Expression<Func<Flight, bool>>, bool> to the "Matches"-method.
Thanks Patrik,
Examining the expression was exactly what I needed to do, i.e. parse the expression (f => f.ID == id) and execute the Right side of the == to get its runtime value.
In code this looks like this:
A.CallTo(() => flightRepository.Single(A<Expression<Func<Flight, bool>>>.That
.Matches(exp => Expression.Lambda<Func<int>>(((BinaryExpression)exp.Body).Right).Compile().Invoke() == 1)))
.Returns(new Flight());
However I can't help thinking that there must be a more elegant way to achieve the same end. I'll leave that for another day though.
Thanks again,
Michael McDowell
I had the same problem while attempting to assert an expression as an argument but I was using Moq. The solution should work for you though as well...
I give most of the credit to this answer to a similar question:
Moq Expect On IRepository Passing Expression
It basically says you can do a ToString() on the expressions and compare them. It is kind of hacky but it only has one downside; the variables names in the lambda expression must match.
Here is an example...
[Test]
public void TestWhichComparesExpressions()
{
// setup
_mockRepository.Setup(x => x.GetByFilter(MatchQuery())).Returns(new List<Record>());
// execute
var records = _service.GetRecordsByFilter();
// assert
Assert.IsNotNull(records);
Assert.AreEqual(0, records.Count());
}
private static Expression<Func<DomainRecord, bool>> MatchQuery()
{
return MatchExpression(ServiceClass.QueryForTheRecords); // constant
}
// https://stackoverflow.com/questions/288413/moq-expect-on-irepository-passing-expression/1120836#1120836
private static Expression<Func<DomainRecord, bool>> MatchExpression(Expression<Func<DomainRecord, bool>> expression)
{
return It.Is<Expression<Func<DomainRecord, bool>>>(e => e.ToString() == expression.ToString());
}
I decided to put the expression into a constant on the class which used it which guaranteed it would be the same in the test if someone changed the lambda expressions's variable names.
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.