I'm looking for suggestions on how to write a query. For each Goal, I want to select the first Task (sorted by Task.Sequence), in addition to any tasks with ShowAlways == true. (My actual query is more complex, but this query demonstrates the limitations I'm running into.)
I tried something like this:
var tasks = (from a in DbContext.Areas
from g in a.Goals
from t in g.Tasks
let nextTaskId = g.Tasks.OrderBy(tt => tt.Sequence).Select(tt => tt.Id).DefaultIfEmpty(-1).FirstOrDefault()
where t.ShowAlways || t.Id == nextTaskId
select new CalendarTask
{
// Member assignment
}).ToList();
But this query appears to be too complex.
System.InvalidOperationException: 'Processing of the LINQ expression 'OrderBy<Task, int>(
source: MaterializeCollectionNavigation(Navigation: Goal.Tasks(< Tasks > k__BackingField, DbSet<Task>) Collection ToDependent Task Inverse: Goal, Where<Task>(
source: NavigationExpansionExpression
Source: Where<Task>(
source: DbSet<Task>,
predicate: (t0) => Property<Nullable<int>>((Unhandled parameter: ti0).Outer.Inner, "Id") == Property<Nullable<int>>(t0, "GoalId"))
PendingSelector: (t0) => NavigationTreeExpression
Value: EntityReferenceTask
Expression: t0
,
predicate: (i) => Property<Nullable<int>>(NavigationTreeExpression
Value: EntityReferenceGoal
Expression: (Unhandled parameter: ti0).Outer.Inner, "Id") == Property<Nullable<int>>(i, "GoalId"))),
keySelector: (tt) => tt.Sequence)' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.'
The problem is the line let nextTaskId =.... If I comment out that, there is no error. (But I don't get what I'm after.)
I'll readily admit that I don't understand the details of the error message. About the only other way I can think of to approach this is return all the Tasks and then sort and filter them on the client. But my preference is not to retrieve data I don't need.
Can anyone see any other ways to approach this query?
Note: I'm using the very latest version of Visual Studio and .NET.
UPDATE:
I tried a different, but less efficient approach to this query.
var tasks = (DbContext.Areas
.Where(a => a.UserId == UserManager.GetUserId(User) && !a.OnHold)
.SelectMany(a => a.Goals)
.Where(g => !g.OnHold)
.Select(g => g.Tasks.Where(tt => !tt.OnHold && !tt.Completed).OrderBy(tt => tt.Sequence).FirstOrDefault()))
.Union(DbContext.Areas
.Where(a => a.UserId == UserManager.GetUserId(User) && !a.OnHold)
.SelectMany(a => a.Goals)
.Where(g => !g.OnHold)
.Select(g => g.Tasks.Where(tt => !tt.OnHold && !tt.Completed && (tt.DueDate.HasValue || tt.AlwaysShow)).OrderBy(tt => tt.Sequence).FirstOrDefault()))
.Distinct()
.Select(t => new CalendarTask
{
Id = t.Id,
Title = t.Title,
Goal = t.Goal.Title,
CssClass = t.Goal.Area.CssClass,
DueDate = t.DueDate,
Completed = t.Completed
});
But this also produced an error:
System.InvalidOperationException: 'Processing of the LINQ expression 'Where<Task>(
source: MaterializeCollectionNavigation(Navigation: Goal.Tasks (<Tasks>k__BackingField, DbSet<Task>) Collection ToDependent Task Inverse: Goal, Where<Task>(
source: NavigationExpansionExpression
Source: Where<Task>(
source: DbSet<Task>,
predicate: (t) => Property<Nullable<int>>((Unhandled parameter: ti).Inner, "Id") == Property<Nullable<int>>(t, "GoalId"))
PendingSelector: (t) => NavigationTreeExpression
Value: EntityReferenceTask
Expression: t
,
predicate: (i) => Property<Nullable<int>>(NavigationTreeExpression
Value: EntityReferenceGoal
Expression: (Unhandled parameter: ti).Inner, "Id") == Property<Nullable<int>>(i, "GoalId"))),
predicate: (tt) => !(tt.OnHold) && !(tt.Completed))' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.'
This is a good example for the need of full reproducible example. When trying to reproduce the issue with similar entity models, I was either getting a different error about DefaulIfEmpty(-1) (apparently not supported, don't forget to remove it - the SQL query will work correctly w/o it) or no error when removing it.
Then I noticed a small deeply hidden difference in your error messages compared to mine, which led me to the cause of the problem:
MaterializeCollectionNavigation(Navigation: Goal.Tasks (<Tasks>k__BackingField, DbSet<Task>)
specifically the DbSet<Task> at the end (in my case it was ICollection<Task>). I realized that you used DbSet<T> type for collection navigation property rather than the usual ICollection<T>, IEnumerable<T>, List<T> etc., e.g.
public class Goal
{
// ...
public DbSet<Task> Tasks { get; set; }
}
Simply don't do that. DbSet<T> is a special EF Core class, supposed to be used only from DbContext to represent db table, view or raw SQL query result set. And more importantly, DbSets are the only real EF Core query roots, so it's not surprising that such usage confuses the EF Core query translator.
So change it to some of the supported interfaces/classes (for instance, ICollection<Task>) and the original problem will be solved.
Then removing the DefaultIfEmpty(-1) will allow successfully translating the first query in question.
I don't have EF Core up and running, but are you able to split it up like this?
var allTasks = DbContext.Areas
.SelectMany(a => a.Goals)
.SelectMany(a => a.Tasks);
var always = allTasks.Where(t => t.ShowAlways);
var next = allTasks
.OrderBy(tt => tt.Sequence)
.Take(1);
var result = always
.Concat(next)
.Select(t => new
{
// Member assignment
})
.ToList();
Edit: Sorry, I'm not great with query syntax, maybe this does what you need?
var allGoals = DbContext.Areas
.SelectMany(a => a.Goals);
var allTasks = DbContext.Areas
.SelectMany(a => a.Goals)
.SelectMany(a => a.Tasks);
var always = allGoals
.SelectMany(a => a.Tasks)
.Where(t => t.ShowAlways);
var nextTasks = allGoals
.SelectMany(g => g.Tasks.OrderBy(tt => tt.Sequence).Take(1));
var result = always
.Concat(nextTasks)
.Select(t => new
{
// Member assignment
})
.ToList();
I would recommend you start by breaking up this query into individual parts. Try iterating through the Goals in a foreach with your Task logic inside. Add each new CalendarTask to a List that you defined ahead of time.
Overall breaking this logic up and experimenting a bit will probably lead you to some insight with the limitations of Entity Framework Core.
I think we might separate the query into two steps. First, query each goals and get the min Sequence task and store them(maybe with a anonymous type like {NextTaskId,Goal}). Then, we query the temp data and get the result. For example
Areas.SelectMany(x=>x.Goals)
.Select(g=>new {
NextTaskId=g.Tasks.OrderBy(t=>t.Sequence).FirstOrDefault()?.Id,
Tasks=g.Tasks.Where(t=>t.ShowAlways)
})
.SelectMany(a=>a.Tasks,(a,task)=>new {
NextTaskId = a.NextTaskId,
Task = task
});
I tried to create the linq request but I'm not sure about the result
var tasks = ( from a in DbContext.Areas
from g in a.Goals
from t in g.Tasks
join oneTask in (from t in DbContext.Tasks
group t by t.Id into gt
select new {
Id = gt.Key,
Sequence = gt.Min(t => t.Sequence)
}) on new { t.Id, t.Sequence } equals new { oneTask.Id,oneTask.Sequence }
select new {Area = a, Goal = g, Task = t})
.Union(
from a in DbContext.Areas
from g in a.Goals
from t in g.Tasks
where t.ShowAlways
select new {Area = a, Goal = g, Task = t});
I currently don't have EF Core, but do you really need to compare this much?
Wouldn't querying the tasks be sufficient?
If there is a navigation property or foreign key defined I could imaging using something like this:
Tasks.Where(task => task.Sequence == Tasks.Where(t => t.GoalIdentity == task.GoalIdentity).Min(t => t.Sequence) || task.ShowAlways);
Using Entity Framework Core 2.2 I have the following query:
IQueryable<User> users = _context.Users.AsNoTracking();
User user = await users
.Include(x => x.UserSkills)
.ThenInclude(x => x.Skill)
.FirstOrDefaultAsync(x => x.Id == 1);
var userSkills = user.UserSkills.ToList();
IQueryable<Lesson> lessons = _context.Lessons.AsNoTracking();
var test = lessons
.Where(x => x.IsEnabled)
.Where(x => x.LessonSkills.All(y => userSkills.Any(z => y.SkillId == z.SkillId)))
.ToList();
I am looking to get User Skills contains all Lesson Skills.
When I run this query I get the following error:
Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.dll:
'Error generated for warning 'Microsoft.EntityFrameworkCore.Query.QueryClientEvaluationWarning:
The LINQ expression 'where ([y].SkillId == [z].SkillId)' could not be translated and will be evaluated locally.'.
How to change the query to solve this problem?
Update
I need to extend this query with an extra option (y.SkillLevelId <= z.SkillLevelId):
var test = lessons
.Where(x => x.IsEnabled)
.Where(x => x.LessonSkills.All(y => userSkills.Any(z =>
y.SkillId == z.SkillId
&&
y.SkillLevelId <= z.SkillLevelId)))
.ToList();
userSkills is in-memory collection, and from my experience with EF6 and EF Core so far I can say that the only reliable translatable construct with in-memory collections is Enumerable.Contains method on primitive type in-memory collection.
So the following solves the problem is question.
First (should be outside the query expression tree):
var userSkillIds = user.UserSkills.Select(x => x.SkillId);
Then instead of
.Where(x => x.LessonSkills.All(y => userSkills.Any(z => y.SkillId == z.SkillId)))
use the equivalent (but translatable):
.Where(x => x.LessonSkills.All(y => userSkillIds.Contains(y.SkillId)))
Update: If you can't use Contains, the options you have until EF Core starts supporting it are (1) EntityFrameworkCore.MemoryJoin package (I personally haven't tested it, but the idea is interesting), (2) manually building Or based predicate with Expression class (hard and works for small memory collections) and (3) replace the memory collection with real IQueryable<>, for instance
var userSkills = users
.Where(x => x.Id == 1)
.SelectMany(x => x.UserSkills);
and use the original query.
I am trying to convert the result of the query into IDictionary
Here string will contain orderId and the int will contain the TradedQuantity
The query below should join three objects Order, OrderRevision and OrderEvent.
1 Order can have many orderRevisions
1 OrderRevision can have many orderEvents
What the query is trying to do is to inner join three objects and get all order objects whose order id matches the list of orderids supplied to it. Then it does a group by based on orderId and gets the latest TradedQuantity from orderEvents object. LatestTradedQuantity will be the TradedQuantityFrom latest OrderEvent. For now the latest orderevent can be regarded as the one that has highest OrderEventId value.
OrderRevision revisionAlias = null;
Order orderAlias = null;
var query =
Session.QueryOver<OrderEvent>()
.JoinAlias(oe => oe.OrderRevision,() => revisionAlias)
.JoinAlias(oe => oe.OrderRevision.Order,() => orderAlias)
.Where(x => x.OrderRevision.Order.SourceSystem.Name.ToLower() == sourceSystem.ToLower())
.WhereRestrictionOn(x => x.OrderRevision.Order.Id).IsIn(orderIds.ToList())
.SelectList(list => list.SelectGroup(x => x.OrderRevision.Order.SourceOrderIdentifier)
.SelectMax(x => x.Id).Select(x => x.TradedQuantity))
.Select(x => new KeyValuePair<string, int?>(x.OrderRevision.Order.SourceOrderIdentifier, x.TradedQuantity)
);
As this query does not do what is supposed to. Could you please help and let me know how the result can be cast into IDictionary?
You have tagged your question with linq-to-nhibernate, so I guess using it instead of queryover would suit you. With Linq, use a sub-query for selecting the "max" order events ids for each order, then query them and project them to a dictionary.
using System.Linq;
using NHibernate.Linq;
...
var orderEventsIdsQuery = Session.Query<OrderEvent>()
.Where(oe => orderIds.Contains(oe.OrderRevision.Order.Id))
.GroupBy(oe => oe.OrderRevision.Order.SourceOrderIdentifier,
(soi, oes) => oes.Max(oe => oe.Id));
var result = Session.Query<OrderEvent>()
.Where(oe => orderEventsIdsQuery.Contains(oe.Id))
.ToDictionary(oe => oe.OrderRevision.Order.SourceOrderIdentifier,
oe => oe.TradedQuantity);
This should do the job. I do not use QueryOver and I will not try to give an answer for doing it with QueryOver.
I have the following queries:
var ground = db
.Ground
.Where(g => g.RowKey == Ground_Uuid)
.ToList();
var building = db
.Building
.Where(b => ground.Any(gr => gr.RowKey == b.Ground.RowKey))
.ToList();
var floor = db
.Floor
.Where(b => building.Any(by => by.RowKey == b.Building.RowKey))
.ToList();
So the second relies on the id from the first set and so on.
I got following error when an execution goes to the second query:
Unable to create a constant value of type 'Domain.Model.Entities.Ground'. Only primitive types or enumeration types are supported in this context.
Any ideas how to resolve it?
The problem with your code is that ToList is converting the result into an in-memory object and a collection of objects in memory cannot be joined with a set of data in the database.
var ground = db.Ground.Where(g => g.RowKey == Ground_Uuid);
var building = db.Building.Where(b => ground.Any(gr => gr.RowKey == b.Ground.RowKey));
var floor = db.Floor.Where(b => building.Any(by => by.RowKey == b.Building.RowKey));
Also, frankly after reading #juharr's comment, I saw the relationship between floor, building & ground. Since you are already doing b.Building.RowKey, b.Ground.RowKey predicting the relationship was easy and I totally agree, it can be simplified as:-
var floor = db.Floor.Where(b => b.Building.Ground.RowKey == Ground_Uuid);
It seems like the first query is redundant. You already know that the RowKey column for each row will be equal to Ground_Uuid.
var building = db.Building.Where(b => b.Ground.RowKey == Ground_Uuid);
var floor = db.Floor.Where(b => b.Building.Ground.RowKey == Ground_Uuid);
Removing ToList() would do the job, but moreover if RowKey is the foreign key you can utilize Linq:
var floor = db.Floor
.Where(b => b.Building.Ground.RowKey == Ground_Uuid)
.ToList();
I'm trying to visit the Entity Framework's Include method using QueryResultCache class which is motioned here. It's a very popular article and a lot of query caching libraries are using it.
When I try an expression like:
var exp1 = context.Products.Include(x => x.Tags)
.Where(x => x.Tags.Any(y => y.Name.Contains("Test")))
.Select(x => new {x.ProductId}).Expression;
with it, it produces this string:
value(System.Data.Entity.Core.Objects.ObjectQuery`1
[EfSecondLevelCaching.Test.Models.Product]).MergeAs(AppendOnly).IncludeSpan
(value(System.Data.Entity.Core.Objects.Span))
.Where(x => x.Tags.Any(y => y.Name.Contains("Test")))
.Select(x => new <>f__AnonymousType5`1(ProductId = x.ProductId))
As you can see, the result doesn't contain the parameters of Include method (x => x.Tags). So most of the linq caching libraries on the net can't create a valid unique query key for the EF queries. How can I fix this?
Edit:
If I remove the select method, it will produce:
value(System.Data.Entity.Core.Objects.ObjectQuery`1
[EfSecondLevelCaching.Test.Models.Product])
.MergeAs(AppendOnly)
.IncludeSpan(value(System.Data.Entity.Core.Objects.Span))
.Where(x => x.Tags.Any(y => y.Name.Contains("Test")))
So here there is no difference between Include(x=>x.Tags) and Include(x=>x.Users).
The query will only return what is in your Select expression. In this case Select(x => new {x.ProductId}) means that only a single field ProductId will be returned.
Your Include would have made a difference if you were returning Products as they contain Tags, but makes no difference if you just have ProductId.
See this MSDN article for more information on eager loading (Include ensures eager loading)