IQueryable<Organization> query = context.Organizations;
Func<Reservation, bool> predicate = r => !r.IsDeleted;
query.Select(o => new {
Reservations = o.Reservations.Where(predicate)
}).ToList();
this query throws "Internal .NET Framework Data Provider error 1025" exception but the query below does not.
query.Select(o => new {
Reservations = o.Reservations.Where( r => !r.IsDeleted)
}).ToList();
I need to use the first one because I need to check a few if statements for constructing the right predicate. I know that I can not use if statements in this circumstance that is why I pass a delegate as parameter.
How can I make the first query work?
While the other answers are true, note that when trying to use it after a select statement one has to call AsQueryable() explicitly, otherwise the compiler will assume that we are trying to use IEnumerable methods, which expect a Func and not Expression<Func>.
This was probably the issue of the original poster, as otherwise the compiler will complain most of the time that it is looking for Expression<Func> and not Func.
Demo:
The following will fail:
MyContext.MySet.Where(m =>
m.SubCollection.Select(s => s.SubItem).Any(expr))
.Load()
While the following will work:
MyContext.MySet.Where(m =>
m.SubCollection.Select(s => s.SubItem).AsQueryable().Any(expr))
.Load()
After creating the bounty (rats!), I found this answer, which solved my problem. (My problem involved a .Any() call, which is a little more complicated than this question...)
In short, here's your answer:
IQueryable<Organization> query = context.Organizations;
Expression<Func<Reservation, bool>> expr = r => !r.IsDeleted;
query.Select(o => new { Reservations = o.Reservations.Where(expr) })
.ToList();
Read the referenced answer for an explanation of why you need the local variable expr, and you can't directly reference another method of return type Expression<Func<Reservation, bool>>.
Thanks for pinging me. I guess I was on the right track after all.
Anyway, to reiterate, LINQ to Entities (thanks to Jon Skeet for correcting me when I got mixed up in my own thought process in the comments) operates on Expression Trees; it allows for a projection to translate the lambda expression to SQL by the QueryProvider.
Regular Func<> works well for LINQ to Objects.
So in this case, when you're using the Entity Framework, any predicate passed to the EF's IQueryable has to be the Expression<Func<>>.
I just experienced this issue in a different scenario.
I have a static class full of Expression predicates which I can then combine or pass to an EF query. One of them was:
public static Expression<Func<ClientEvent, bool>> ClientHasAttendeeStatus(
IEnumerable<EventEnums.AttendeeStatus> statuses)
{
return ce => ce.Event.AttendeeStatuses
.Where(a => a.ClientId == ce.Client.Id)
.Select(a => a.Status.Value)
.Any(statuses.Contains);
}
This was throwing the 1025 error due to the Contains method group call. The entity framework expected an Expression and found a method group, which resulted in the error. Converting the code to use a lambda (which can be implicitly cast to an Expression) fixed the error
public static Expression<Func<ClientEvent, bool>> ClientHasAttendeeStatus(
IEnumerable<EventEnums.AttendeeStatus> statuses)
{
return ce => ce.Event.AttendeeStatuses
.Where(a => a.ClientId == ce.Client.Id)
.Select(a => a.Status.Value)
.Any(x => statuses.Contains(x));
}
Aside: I then simplified the expression to ce => ce.Event.AttendeeStatuses.Any(a => a.ClientId == ce.Client.Id && statuses.Contains(a.Status.Value));
Had a similar problem. Library of ViewModels that look like this:
public class TagViewModel
{
public int Id { get; set; }
public string Name { get; set; }
public static Expression<Func<SiteTag, TagViewModel>> Select = t => new TagViewModel
{
Id = t.Id,
Name = t.Name,
};
This works:
var tags = await db.Tags.Take(10).Select(TagViewModel.Select)
.ToArrayAsync();
But, this won't compile:
var post = await db.Posts.Take(10)
.Select(p => new {
Post = p,
Tags = p.Tags.Select(pt => pt.Tag).Select(TagViewModel.Select)
})
.ToArrayAsync();
Because the second .Select is a mess - the first one is actually called off of an ICollection, which is not IQueryable, so it consumes that first Expression as a plain Func, not Expression<Func.... That returns IEnumerable<..., as discussed on this page. So .AsQueryable() to the rescue:
var post = await db.Posts.Take(10)
.Select(p => new {
Post = p,
Tags = p.Tags.Select(pt => pt.Tag).AsQueryable()
.Select(TagViewModel.Select)
})
.ToArrayAsync();
But that creates a new, weirder problem: Either I get Internal Framework...Error 1025, or I get the post variable with a fully loaded .Post property, but the .Tags property has an EF proxy object that seems to be used for Lazy-Loading.
The solution is to control the return type of Tags, by ending use of the Anonymous class:
public class PostViewModel
{
public Post Post { get; set; }
public IEnumerable<TagViewModel> Tags { get; set; }
Now select into this and it all works:
var post = await db.Posts.Take(10)
.Select(p => new PostViewModel {
Post = p,
Tags = p.Tags.Select(pt => pt.Tag).AsQueryable()
.Select(TagViewModel.Select)
})
.ToArrayAsync();
Related
I am fairly new to C# and .Net, so apologies if something doesn't make sense, I will try my best to explain my problem.
I have two methods which are basically going to use the similar query but with slight differences. So instead of repeating the query in both methods I created a third private method which will return the common part of the query and then the functions can add more clauses in query as they require.
Here is a generic function which returns the IQueryable object with common part of the query
private IQueryable<OfferViewModel> GetOffersQueryForSeller(int sellerId)
{
return Db.Offers
.Where(o => o.Sku.SellerId == sellerId && o.IsActive && !o.IsDiscontinued)
.Select(o => new OfferViewModel
{
Id = o.Id,
Name = o.Sku.Name,
ImageUrl = o.Sku.ImageUrl ?? o.Sku.Upcq.Upc.ImageUrl,
QuantityName = o.Sku.QuantityName
});
}
Following are the two method which are reusing the IQueryable object
public async Task<List<OfferViewModel>> GetSellerOffers(int sellerId)
{
var query = GetOffersQueryForSeller(sellerId);
return await query.ToListAsync();
}
public async Task<List<OfferViewModel>> GetDowngradableSellerOffers(int sellerId)
{
var query = GetOffersQueryForSeller(sellerId);
return await query
.Where(o => o.Sku.Id == monthlySkuId)
.ToListAsync();
}
Now GetSellerOffers works just fine but GetDowngradableSellerOffers throws a run time error with message The specified type member 'Sku' is not supported in LINQ to Entities.. I asked around and one of the guys told me that I cannot add additional where after adding a select which uses a ViewModel because then my records will be mapped to ViewModel and LINQ will attempt to look up props of ViewModel instead of database columns.
Now I have two questions,
In the docs I read Entity Framework will only run query when I try to fetch the results with methods like ToList and if I haven't done that why it wouldn't allow me to apply conditions on database fields/
How can I reuse the common query in my scenario?
How about the following code:
(The type Offer should be replaced by the type of the Elements that Db.Offers holds)
private IQueryable<OfferViewModel> GetOffersQueryForSeller(int sellerId, Func<Offer,bool> whereExtension)
{
return Db.Offers
.Where(o => ... && whereExtension.Invoke(o))
.Select(o => new OfferViewModel { ... });
}
private IQueryable<OfferViewModel> GetOffersQueryForSeller(int sellerId)
{
return GetOffersQueryForSeller(sellerId, (o) => true);
}
And then call it in GetDowngradableSellerOffers like this:
public async Task<List<OfferViewModel>> GetDowngradableSellerOffers(int sellerId)
{
var query = GetOffersQueryForSeller(sellerId, (o) => o.Sku.Id == monthlySkuId);
return await query.ToListAsync();
}
I have a number of similar methods that contain linq queries - here's an example. The only difference is the .Where clause fed by the param.
public Supplier FindAny(int ID)
{
return CompareView.Select()
.Where(p => p.Supplier.ID == ID)
.Select(p => p.Supplier)
.FirstOrDefault();
}
I'm looking to see whether the code can be slimmed down through the use of expressions. To date I've found a few examples of expressions in use, but nothing that has helped me convert the code successfully.
Firstly, it would be good to know if expressions can be utilised with this style of code, and if it can, any pointers would be appreciated.
A straight forward translation would be:
public Supplier FindAny(Func<WhateverTypePIs, bool> func)
{
return CompareView.Select()
.Where(func)
.Select(p => p.Supplier)
.FirstOrDefault();
}
..which would allow this:
var supplier = FindAny(p => p.Supplier.ID == ID);
Note: You'll have to fill in the WhateverTypePIs generic type .. as that isn't shown in your original question (it's whatever p's type is in your current expression).
Does this help:
public Supplier FindAny(Func<WhateverTypePIs, bool> func)
{
return CompareView.FirstOrDefault(func).Supplier
}
I have something like this:
Func<Thread, bool> tmpFunc = thread => true;
threads = Threads.Where(tmpFunc).(...)
Now, when I do Threads.Where(thread => true).(...) everything is okay, but using variable in .Where() crashes my application. Why? Am I doing something wrong?
Okay, so here is the code that reproduces the error:
var threads = context.Categories
.Where(c => c.Name == variable)
.Select(c => new
{
threads = c.Threads
.Where(tmpFunc)
.OrderByDescending(t => t.DateCreated)
.Skip(threadsToSkip)
.Take(threadsPerPage)
.Select(t => new
{
t,
CategoryName = t.Category.Name,
AuthorName = t.Author.UserName,
t.Posts.Count,
LastPost = t.Posts
.OrderByDescending(post => post.DateCreated)
.Select(p => new{p.Author.UserName, p.DateCreated})
.FirstOrDefault()
}),
c.Threads.Count
}).Single();
And the error it gives me is internal .net framework data provider error 1025
Try using an Expression instead of the Func directly:
Expression<Func<Thread, bool>> tmpFuncExpr = thread => true;
While Linq2Objects will be happy with the Func, Linq2Sql will not.
My assumption is that there is no translatiin of a custom func to sql and the func is used in the projection. Although I would expect a "no sql translation for ... exists" exception.
To fix this, you could try declare your func as
Expression<Func<Thread, bool>> tmpFunc = thread => true;
threads = Threads.Where(tmpFunc).(...)
When you're using the Entity Framework, any predicate passed to the EF's IQueryable has to be the Expression<Func<>>.
Check this answer stackoverflow.com/questions/11990158...
Consider the following code
var q = from e in myCollection.AsQueryable<Entity>() where e.Name == "test" select e;
The actual query is very complex and I don't like building it using QueryBuilder instead of LINQ.
So I want to convert it back to IMongoQuery to use in myCollection.Group() call since there is no GroupBy support through LINQ.
Is it possible?
Edited answer:
I realized that there already is an official way to get the Mongo query from a LINQ query (I should have known!). You have to downcast the IQueryable<T> to a MongoQueryable<T> to get access to the GetMongoQuery method:
var linqQuery = from e in collection.AsQueryable<Entity>() where e.Name == "test" select e;
var mongoQuery = ((MongoQueryable<Entity>)linqQuery).GetMongoQuery();
Original answer:
At the moment there is no officially supported way to do that, but in the near future we do intend to make it easy to find out what MongoDB query the LINQ query was mapped to.
In the short term you could use the following undocumented internal methods to find out what MongoDB query the LINQ query is mapped to:
var linqQuery = from e in collection.AsQueryable<Entity>() where e.Name == "test" select e;
var translatedQuery = (SelectQuery)MongoQueryTranslator.Translate(linqQuery);
var mongoQuery = translatedQuery.BuildQuery();
But at some point you might need to switch from these undocumented methods to officially supported methods (the undocumented methods might change or be renamed in the future).
A quick extension based on Robert Stam's answer:
public static IMongoQuery ToMongoQuery<T>(this IQueryable<T> linqQuery)
{
var mongoQuery = ((MongoQueryable<T>)linqQuery).GetMongoQuery();
return mongoQuery;
}
public static WriteConcernResult Delete<T>(this MongoCollection<T> col, IQueryable<T> linqQuery)
{
return col.Remove(linqQuery.ToMongoQuery());
}
public static WriteConcernResult Delete<T>(this MongoCollection<T> col, Expression<System.Func<T, bool>> predicate)
{
return col.Remove(col.AsQueryable<T>().Where(predicate).ToMongoQuery());
}
example:
myCollection.Remove(myCollection.AsQueryable().Where(x => x.Id == id).ToMongoQuery());
myCollection.Delete(myCollection.AsQueryable().Where(x => x.Id == id));
myCollection.Delete(x => x.Id == id);
I have made myself an ExpressionBuilder class that helps me put together expressions that can be used as a predicate when doing Linq to Sql queries. It has worked great. However, I just discovered Expressions can only be used to filter on Tables, and not on EntitySets??Why on earth is this the case?
For example if I have Company and an Employee with a Salary. I could create these two expressions:
Expression<Func<Company, bool>> cp = x => x.Name.StartsWith("Micro");
Expression<Func<Employee, bool>> ep = x => x.Name.StartsWith("John");
I would then expect to be able to do the following, however it only partially works:
var companies = dataContext.Companies
.Where(cp) // Goes fine
.Select(x => new
{
x.Name,
SumOfSalaries = x.Employees
.Where(ep) // Causes compile-time error
.Sum(y => y.Salary),
}
.ToList();
Also, if I do a ep.Compile() it compiles, but then I get an error when running the query.
Why is this the case? Am I missing something? I don't find this logical. Can I fix this somehow? Or do you have a good workaround?
I know that I in this case could just use Where(x => x.Name.StartsWith("John")) instead, but the problem is that the expressions I need are not that trivial. They are longer strings of AndAlsos and OrElses.
If you are going to pass a lambda expression to a LINQ to SQL provider don't create it as an Expression<T> - let the provider do that for you.
The following works for me - note both are compiled:
var companies = dataContext.Companies.Where(cp.Compile())
.Select(x => new
{
x.Name,
SumOfSalaries = x.Employees
.Where( ep.Compile() )
.Sum(y => y.Salary),
}
).ToList();
The expression parser seems to be losing type information in there somewhere after the first where clause when you put in the second. To be honest, I'm not sure why yet.
Edit: To be clear, I do understand that EntitySet doesn't support passing an expression into the where clause. What I don't completely understand is why it fails when you add the Where(ep.Compile()).
My theory is that in compiling the first where (Where(cp.Compile()), Linq2Sql quits parsing the expression - that it can't parse the ep.Compile() against an entityset, and is unable to decide to break up the query into two until you compile the first where clause.
I think you need to rewrite your query. Another way to ask for the details you want, is: "Give me the sum of the salaries for the selected employees in the selected companies, organized by the company name".
So, with the employee salaries in focus, we can write:
//Expression<Func<Employee, bool>> ep = x => x.Name.StartsWith("John");
//Expression<Func<Company, bool>> cp = x => x.Name.StartsWith("Micro");
Expression<Func<Employee, bool>> ep = x => x.Name.StartsWith("John");
Expression<Func<Employee, bool>> cp = x => x.Company.Name.StartsWith("Micro");
var salaryByCompany = dataContext.Employees
.Where(ep)
.Where(cp)
.GroupBy(employee => employee.Company.Name)
.Select(companyEmployees => new
{
Name = companyEmployees.Key,
SumOfSalaries = companyEmployees.Sum(employee => employee.Salary)
});
var companies = salaryByCompany.ToList();