how come this work
public IQueryable<Category> getCategories(int postId)
{
subnusMVCRepository<Categories> categories = new subnusMVCRepository<Categories>();
subnusMVCRepository<Post_Category_Map> postCategoryMap = new subnusMVCRepository<Post_Category_Map>();
var query = from c in categories.GetAll()
join pcm in postCategoryMap.GetAll() on c.CategoryId equals pcm.CategoryId
where pcm.PostId == 1
select new Category
{
Name = c.Name,
CategoryId = c.CategoryId
};
return query;
}
but this does not
public IQueryable<Category> getCategories(int postId)
{
subnusMVCRepository<Categories> categories = new subnusMVCRepository<Categories>();
subnusMVCRepository<Post_Category_Map> postCategoryMap = new subnusMVCRepository<Post_Category_Map>();
var query = from c in categories.GetAll()
join pcm in postCategoryMap.GetAll() on c.CategoryId equals pcm.CategoryId
where pcm.PostId == postId
select new Category
{
Name = c.Name,
CategoryId = c.CategoryId
};
return query;
}
The issue is most likely in the implementation of the query provider.
pcm.PostId == 1
and
pcm.PostId == postId
actually have a big difference. In the expression tree the first is generated as a ConstantExpression which doesnt need to be evaulated.
With the second, the compiler actually generates an inner class here (this is the _DisplayClassX that you see). This class will have a property (will most likely be the same name as your parameter) and the expression tree will create a MemberAccessExpression which points to the auto-generated DisplayClassX. When you query provider comes accross this you need to Compile() the Lambda expression and evaluate the delegate to get the value to use in your query.
Hope this helps.
cosullivan
The problem is not the linq itself,
you need to be sure that the context or provider object is able to fetch the data.
try testing the
subnusMVCRepository<Categories> categories = new subnusMVCRepository<Categories>();
subnusMVCRepository<Post_Category_Map> postCategoryMap = new subnusMVCRepository<Post_Category_Map>();
objects and see if they are populated or if they behaving as required.
you may want to search the generated code for c__DisplayClass1 and see what you can see there. some times the generated code dose some weird things.
when you step into you code check the locals and the variable values. this may also give you some clues.
Edit : Have you tried to return a List<> collection ? or an Enumerable type?
Edit : What is the real type of the item and query may not be iterable
Related
I need to get the following code to work
public IQueryable<BankingDTO> Get(ODataQueryOptions<TillSummaryDTO> options)
{
return((IQueryable<BankingDTO>)options.ApplyTo(this._bankingService.GetBanking()));
}
I would like to query on TillSummaryDTO because it has the field "TillOpID" on it. However I would like to return BankingDTO as this is the end result which contains the group by and sum. When I run the query I receive the error "Cannot apply ODataQueryOptions of 'Bepoz.Presentation.ViewModels.TillSummaryDTO' to IQueryable of 'Bepoz.Presentation.ViewModels.BankingDTO" what is the best practice for this?
The bankingservice.GetBanking method looks like this
var query = from t in _tillSummaryRepository.Table
join w in _workStationRepository.Table on t.TillOpID equals w.WorkstationID
join s in _storeRepository.Table on w.StoreID equals s.StoreID
join v in _venueRepository.Table on s.VenueID equals v.VenueID
select new TillSummaryDTO
{
TillOpID = t.TillOpID,
Cash = t.Cash,
Workstation = new WorkstationDTO()
{
WorkstationID = w.WorkstationID,
Name = w.Name,
Store = new StoreDTO()
{
StoreID = s.StoreID,
StoreGroup = s.StoreGroup,
Name = s.Name,
Venue = new VenueDTO()
{
VenueID = v.VenueID,
VenueGroup = v.VenueGroup,
Name = v.Name,
}
}
}
};
return query.GroupBy(x => x.Workstation.Name)
.Select(x => new BankingDTO()
{
TotalCash = x.Sum(y => y.Cash),
WorkstationName = x.Key
});
The scenario you want to achieve is that you have an entity set of TillSummaryDTO that you want to query, and you would like the return type to be a collection of BankingDTO. The query for the BankingDTO is carried out by applying the query options in the URL onto TillSummaryDTO . But the fact that the BankingDTO and TillSummaryDTO are different kind of types makes it impossible achieve that in a simple Get action method, right?
This scenario can be better resolved by the function feature of the OData protocol that the function takes the TillSummaryDTO collection as input parameter, has some internal complicated logic to query for the right BankingDTO, and returns the BankingDTO instead of TillSummaryDTO.
For the concept of function in OData protocol, you can refer to this link for V4 and section "10.4.2. Functions" of this page for V3.
For implementation, this sample can be referred to for Web API OData V4 and this tutorial can be referred to for Web API OData V3.
var result=(from refridgerators in context.A
group refridgerators by new { refridgerators.Id, refridgerators.Name } into gr
select new DAO<String>
{
Key = gr.Key.Name,
Count = gr.Count()
}).OrderByDescending(k => k.Count).Take(numberOfRecords).ToList();
This is my linq to sql query this is working perfectly fine.
this shows top 5 records (sorted by their count) if i pass numberOfRecords =5.
now my problem is i don`t want to modify query. so what should i do in above query to show all records. This is in relation with my requirement i want to use same query to show all refridgerators and Top 5 , top 10 refridgerators.
I am not sure if it is possible using LINQ. but i guess there must be something related to this.
I would simply don't add the Take to the query but to the code where you consume this query.
So for example:
public static IEnumerable<DAO> GetRefrigerators()
{
var query = from refridgerators in context.A
group refridgerators by new { refridgerators.Id, refridgerators.Name } into gr
select new DAO<String>
{
Key = gr.Key.Name,
Count = gr.Count()
};
return query.OrderByDescending(k => k.Count);
}
Now you can either use:
var refrigerators = GetRefrigerators().Take(5).ToList();
or
var refrigerators = GetRefrigerators().Take(10).ToList();
or
var refrigerators = GetRefrigerators().ToList();
I'd make numberOfRecords a int? and if the value is null you should not call Take(numberOfRecords)
var result = (from refridgerators in context.A
group refridgerators by new { refridgerators.Id, refridgerators.Name } into gr
select new DAO<String>
{
Key = gr.Key.Name,
Count = gr.Count()
}).OrderByDescending(k => k.Count);
if(numberOfRecords.HasValue)
result = result.Take(numberOfRecords.Value);
return result.ToList();
I know it changes your query a little bit but I believe it is pretty acceptable, adding a numberOfRecords of a super high value adds an overheard to your query which isn't useful in your case.
So this post is very old, I know, but my solution is not provided (maybe someone wants to achieve the same after 2 years, like me):
You could create your own extension-method that also works with linq 2 sql. Example:
public static class LinqExtensions
{
public static IEnumerable<TResult> TakeIfNotNull<TResult>(this IEnumerable<TResult> source, int? count)
{
return !count.HasValue ? source : source.Take(count.Value);
}
}
this takes an int? instead of int and returns either the source-enumerable if count is null else it returns the result of default Take-method.
So you could write like:
.OrderByDescending(k => k.Count).TakeIfNotNull(numberOfRecords).ToList();
if numberOfCounts is null, it'll take all records.
As the right solution has already been posted by Tim, still I want your attention to the simpler solution, if suits to your requirement.
Add one more if condition at the top of this query.
if(allRecordRequired)
{
numberOfRecords = 2000000;
}
Leave your query as it is.
Pass a huge number to your method.A number that is equal (at least) or bigger than the items count.That should give you all records.
I currently have a LINQ query written in one my controllers that I want to return a single blog post (based off a model) with corresponding comments and topics.
This is what I currently have as my query which I used to return a list of all my blog posts for the home page. I added "where p.id == id (which is the parameter taken in by the ActionResult to fetch the correct post.
var post = from p in db.Set<BlogPost>()
where p.id == id
select new PostViewModel
{
Id = p.id,
Title = p.Title,
DateCreated = p.DateCreated,
Content = p.Content,
Topics = p.Topics,
Comments = p.Comments,
CommentCount = p.Comments.Count
};
return View(post);
The return currently is sending an IQueryable when I just want it to be a single post. Currently I have a foreach in my razor view which is useless and wrong but it works. How can I change this to do what I want?
You can do:
return View(post.SingleOrDefault());
Or if you want to have an exception in the case list is empty:
return View(post.Single());
Just add First() or Single() (which one is right for you depends on context) to your query:
return View(post.First());
It sound like you want to use First or Single:
return View(post.Single());
The difference between them is that Single will throw an exception if more than one matching row is found.
Just do post.First() that should do the trick. Really any function that produces a concrete value will work. First, FirstOrDefault, Single, SingleOrDefault, ToList, or ToArray
I have included the links to each method so you can see what works for you. It sounds like you will want a First or Single variation, depending on if you want errors if more than one post is pulled
replace your LINQ with this
var post = (from p in db.Set<BlogPost>()
where p.id == id
select new PostViewModel
{
Id = p.id,
Title = p.Title,
DateCreated = p.DateCreated,
Content = p.Content,
Topics = p.Topics,
Comments = p.Comments,
CommentCount = p.Comments.Count
}).FirstOrDefault();
I am working with code first approach in EDM and facing an error for which I can't the solution.Pls help me
LINQ to Entities does not recognize the method 'Boolean
CheckMeetingSettings(Int64, Int64)' method, and this method cannot be
translated into a store expression.
My code is following(this is the query which I have written
from per in obj.tempPersonConferenceDbSet
where per.Conference.Id == 2
select new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327,per.Person.Id)
}
public bool CheckMeetingSettings(int,int)
{
///code I have written.
}
Please help me out of this.
EF can not convert custom code to SQL. Try iterating the result set and assigning the property outside the LINQ query.
var people = (from per in obj.tempPersonConferenceDbSet
where per.Conference.Id == 2
order by /**/
select new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
}).Skip(/*records count to skip*/)
.Take(/*records count to retrieve*/)
.ToList();
people.ForEach(p => p.CanSendMeetingRequest = CheckMeetingSettings(6327, p.Id));
With Entity Framework, you cannot mix code that runs on the database server with code that runs inside the application. The only way you could write a query like this, is if you defined a function inside SQL Server to implement the code that you've written.
More information on how to expose that function to LINQ to Entities can be found here.
Alternatively, you would have to call CheckMeetingSettings outside the initial query, as Eranga demonstrated.
Try:
var personDetails = obj.tempPersonConferenceDbSet.Where(p=>p.ConferenceId == 2).AsEnumerable().Select(p=> new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327,per.Person.Id)
});
public bool CheckMeetingSettings(int,int)
{
///code I have written.
}
You must use AsEnumerable() so you can preform CheckMeetingSettings.
Linq to Entities can't translate your custom code into a SQL query.
You might consider first selecting only the database columns, then add a .ToList() to force the query to resolve. After you have those results you van do another select where you add the information from your CheckMeetingSettings method.
I'm more comfortable with the fluid syntax so I've used that in the following example.
var query = obj.tempPersonConferenceDbSet
.Where(per => per.Conference.Id == 2).Select(per => new { Id = per.Person.Id, JobTitle = per.Person.JobTitle })
.ToList()
.Select(per => new PersonDetails { Id = per.Id,
JobTitle = per.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327, per.Person.Id) })
If your CheckMeetingSettings method also accesses the database you might want to consider not using a seperate method to prevent a SELECT N+1 scenario and try to express the logic as part of the query in terms that the database can understand.
OK I'm banging my head against a wall with this one ;-)
Given tables in my database called Address, Customer and CustomerType, I want to display combined summary information about the customer so I create a query to join these two tables and retrieve a specified result.
var customers = (from c in tblCustomer.All()
join address in tblAddress.All() on c.Address equals address.AddressId
join type in tblCustomerType.All() on c.CustomerType equals type.CustomerTypeId
select new CustomerSummaryView
{
CustomerName = c.CustomerName,
CustomerType = type.Description,
Postcode = address.Postcode
});
return View(customers);
CustomerSummaryView is a simple POCO
public class CustomerSummaryView
{
public string Postcode { get; set; }
public string CustomerType { get; set; }
public string CustomerName { get; set; }
}
Now for some reason, this doesn't work, I get an IEnumerable list of CustomerSummaryView results, each record has a customer name and a postcode but the customer type field is always null.
I've recreated this problem several times with different database tables, and projected classes.
Anyone any ideas?
I can't repro this issue - here's a test I just tried:
[Fact]
public void Joined_Projection_Should_Return_All_Values() {
var qry = (from c in _db.Customers
join order in _db.Orders on c.CustomerID equals order.CustomerID
join details in _db.OrderDetails on order.OrderID equals details.OrderID
join products in _db.Products on details.ProductID equals products.ProductID
select new CustomerSummaryView
{
CustomerID = c.CustomerID,
OrderID = order.OrderID,
ProductName = products.ProductName
});
Assert.True(qry.Count() > 0);
foreach (var view in qry) {
Assert.False(String.IsNullOrEmpty(view.ProductName));
Assert.True(view.OrderID > 0);
Assert.False(String.IsNullOrEmpty(view.CustomerID));
}
}
This passed perfectly. I'm wondering if you're using a reserved word in there?
This post seems to be referring to a similar issue...
http://groups.google.com/group/subsonicproject/browse_thread/thread/2b569539b7f67a34?hl=en&pli=1
Yes, the reason Rob's example works is because his projection's property names match exactly, whereas John's original example has a difference between CustomerType and type.Description.
This shouldn't have been a problem, but it was - the Projection Mapper was looking for properties of the same name and wasn't mapping a value if it didn't find a match. Therefore, your projection objects' properties would be default values for its type if there wasn't an exact name match.
The good news is, I got the latest source today and built a new Subsonic.Core.dll and the behavior is now fixed.
So John's code above should work as expected.
I just downloaded the latest build from 3/21/2010, which is about 2 months after the last poster on this thread, and the problem still exists in the packaged binary. Bummer.
Here what I have to do:
var data =
(from m in Metric.All()
where m.ParentMetricId == parentId
select new
{
m.MetricName,
m.MetricId,
})
.ToList();
var treeData =
from d in data
select new TreeViewItem
{
Text = d.MetricName,
Value = d.MetricId.ToString(),
LoadOnDemand = true,
Enabled = true,
};
return new JsonResult { Data = treeData };
If I try to do the projection directly from the Subsonic query, the Text property ends up with the ID, and the Value property ends up with the Name. Very strange.