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've got a table
Application
ApplicationID,
NAme
ApplicationSteps
AplicationStepID,
AplicationID,
StepID
ApplicationStepCriterias
ApplicationStepID,
CriteriaID
So I've got one SelectedCriteriaID - a user choose from a dropdown one criteria and he wants all the applications which has this SelectedCriteriaID in the table ApplicationStepCriterias
I tried
var ds = context.Applications
.Where(a => a.ApplicationSteps
.Select(x=>x.ApplicationStepCriterias
.Select(t=>t.CriteriaId))
.Contains(SelectesdCriteria));
But as I have as result IEnumerable<IEnumerable<int>> I cannot use Contains
Just I get a list of all the CriteriaIds for each ApplicationStep(also a sequence). Just I cannot think of way to get in one list all the CriteriIds.
First, let me try to get the names right. This is not a pure many-to-many association, because the junction class is part of the class model. It is what I unofficially call a 1-n-1 association. So you have
Application -< ApplicationSteps >- ApplicationStepCriterias
I'd strongly recommend to use singular names for your classes ...
Application -< ApplicationStep >- ApplicationStepCriterion
... so you can use plural for collection property names without getting confused.
If I'm right so far, you query should be
context.Applications
.Where(a => a.ApplicationSteps
.Any(x => selectedCriteria
.Contains(x.ApplicationStepCriterion.CriteriaId));
(and I'd also prefer CriterionId, probably referring to a Criterion class)
You may try something like this:
var applicationStepIds = context.ApplicationStepCriterias
.Where(i => i.CriteriaID == selectedCriteria)
.Select(i => i.ApplicationStepID)
.Distinct();
var applicationIds = context.ApplicationSteps
.Where(i => applicationStepIds.Contains(i.AplicationStepID))
.Select(i => i.AplicationID)
.Distinct();
var result = context.Applications.Where(i => applicationIds.Contains(i.ApplicationId));
Running this query:
var holderAccounts = db.AccountDetails.Include(p => p.BranchDetail)
.Where(p => holder.AccountDetails.Any(a => a.Id == p.Id));
I get this exception:
Unable to create a constant value of type 'CodeFirst.AccountDetail'. Only primitive types or enumeration types are supported in this context.
Relationships are:
AccountHolder 1 to many AccountDetail 1 to 1 BranchDetail
What am I doing wrong?
Try extracting the relevant Ids first:
var accountDetailIds = holder.AccountDetails.Select(a => a.Id);
var holderAccounts = db.AccountDetails
.Include(p => p.BranchDetail)
.Where(p => accountDetailIds.Contains(p.Id));
Most likely, Any() is not supported. Try this query:
var ids = holder.AccountDetails.Select(x => x.Id).ToList();
var holderAccounts = db.AccountDetails.Include(p => p.BranchDetail)
.Where(p => ids.Contains(p.Id));
I think what you are trying to do is the same as a SQL Where-In Clause. As Jeffery Khan mentioned, I would extract the criteria that you are going to query against and then perform the query in a separate statement. Hopefully this article will help you understand this good practice used to enhance the readability of the query.
I have 3 entities: Banners, Packs and Files.
One Banner has many packs and one pack has many files.
I need to get all the files ids for all banners. I tried the following:
IList<BannerModel> banners = context.Banners
.OrderBy(x => Guid.NewGuid())
.Take(count)
.Select(x =>
new BannerModel {
Images = x.Packs.SelectMany(p => p.Files.Select(f => f.Id)).ToList()
}).ToList();
However, I am getting an error on the Files id selecting:
System.NotSupportedException: LINQ to Entities does not recognize the
method 'System.Collections.Generic.List1[System.Int32]
ToList[Int32](System.Collections.Generic.IEnumerable1[System.Int32])'
method, and this method cannot be translated into a store expression.
at
System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.DefaultTranslator.Translate(ExpressionConverter
parent, MethodCallExpression call) at ...
Any idea of what might be wrong?
NOTE: I have Lazy Loading disabled.
var allFileIDs = context.Banners.SelectMany(b =>
b.Packs.SelectMany(p => p.Files.Select(f => f.ID)))
.ToList();
Resulting SQL will look like:
SELECT [t2].[ID]
FROM [Banners] AS [t0], [Packs] AS [t1], [Files] AS [t2]
WHERE ([t1].[BannerID] = [t0].[ID]) AND ([t2].[PackID] = [t1].[ID])
No lazy-loading, single query.
Misunderstood your question about getting all file ids. If you need to project each banner to BannerModel:
context.Banners.Select(b => new BannerModel {
Images = b.Packs.SelectMany(p => p.Files.Select(f => f.ID))
}).ToList();
You see exception, because you have ToList() in expression, which cannot be converted into SQL. Change BannerModel.Images to be of type IEnumerable<int> instead of List<int>, and remove ToList() call from select statement.
One more option if you don't want to change type of BannerModel.Images:
context.Banners.Select(b => b.Packs.SelectMany(p => p.Files.Select(f => f.ID)))
.ToList() // brings next projection into memory
.Select(ids => new BannerModel { Images = ids.ToList() })
.ToList();