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.
Related
I am trying to populate a ViewModel in an MVC app with data from a parent table joined with a child table. The only data I want from the child table is a comma diliminated string from the Nomenclature field of the top three records and put them into a string field in the ViewModel. Here is what I have tried without success:
public IEnumerable<ReqHeaderVM> GetOpenReqs(string siteCode)
{
var openReqs = from h in context.ReqHeaders
join l in context.ReqLineItems on h.ID equals l.ReqID into reqLineItems
select new ReqHeaderVM
{
ReqID = h.ID,
ShopCode = h.ShopCode
Nomenclatures = reqLineItems.Select(x => x.Nomenclature).Take(3) // This doesn't work
};
return (openReqs.ToList());
}
Here is the ViewMdel:
public class ReqHeaderVM
{
[Editable(false)]
public string ReqID { get; set; }
public string ShopCode { get; set; }
public string Nomenclatures {get; set;}
}
Assuming that you have proper relationship (foreign key) between ReqHeaders and ReqLineItems, this should give you what you are looking for...
public IEnumerable<ReqHeaderVM> GetOpenReqs(string siteCode)
{
var openReqs = from h in context.ReqHeaders
select new
{
ReqID = h.ID,
ShopCode = h.ShopCode
Nomenclatures = h.ReqLineItems
.OrderBy(x => x.SomeColumn)
.Select(x => x.Nomenclature)
.Take(3)
};
var openReqsTran = from oreq in openReqs.AsEnumerable()
select new ReqHeaderVM
{
oreq.ReqID,
oreq.ShopCode,
Nomenclatures = string.Join(", ", oreq.Nomenclatures)
};
return (openReqsTran);
}
Note that Nomenclatures is a list of type of Nomenclature.
Yes, the join creates a single Cartesian result set. (think tabular data) what you are attempting to do. To get the results you want you have a few choices.
use lazy loading and iterate over each header querying the line items individually.
pro - simple queries
con - select n+1
query all headers and all line items, but build view model with only the top 3
pro - single query
con - large Cartesian result set query too much data
query all headers and all associated lines individuals
pro - 2 smaller, simpler queries
con - query too many line details.
query all headers and top 3 lines per header in 2 queries
pro - get only the information you require
con - complex query for top 3 lines per header.
Lets say I have a generic list of the the following objects:
public class Supermarket
{
public string Brand { get; set; }
public string Suburb { get; set; }
public string State { get; set; }
public string Country { get; set; }
}
So using a List<Supermarket> which is populated with many of these objects with different values I am trying to:
Select the distinct Suburb properties from a
superset of Supermarket objects contained in a List<Supermarket> (say this superset contains 20
distinct Suburbs).
Join the Distinct List of Suburbs above to another set of aggregated and counted Suburbs obtained by a LINQ query to a different, smaller list of List<Supermarket>
The distinct items in my superset are:
"Blackheath"
"Ramsgate"
"Penrith"
"Vaucluse"
"Newtown"
And the results of my aggregate query are:
"Blackheath", 50
"Ramsgate", 30
"Penrith", 10
I want to join them to get
"Blackheath", 50
"Ramsgate", 30
"Penrith", 10
"Vaucluse", 0
"Newtown", 0
Here is what I have tried so far:
var results = from distinctSuburb in AllSupermarkets.Select(x => x.Suburb).Distinct()
select new
{
Suburb = distinctSuburb,
Count = (from item in SomeSupermarkets
group item by item.Suburb into aggr
select new
{
Suburb = aggr.Key,
Count = aggr.Count()
} into merge
where distinctSuburb == merge.Suburb
select merge.Count).DefaultIfEmpty(0)
} into final
select final;
This is the first time I have had to post on Stack Overflow as its such a great resource, but I can't seem to cobble together a solution for this.
Thanks for your time
EDIT: OK So I solved this a short while after the initial post. The only thing I was missing was chaining a call to .ElementAtOrDefault(0) after the call to .DefaultIfEmpty(0). I also verifed that using .First() instead of .DefaultIfEmpty(0) as Ani pointed out worked, The correct query is as follows:
var results = from distinctSuburb in AllSupermarkets.Select(x => x.Suburb).Distinct()
select new
{
Suburb = distinctSuburb,
Count = (from item in SomeSupermarkets
group item by item.Suburb into aggr
select new
{
Suburb = aggr.Key,
Count = aggr.Count()
} into merge
where distinctSuburb == merge.Suburb
select merge.Count).DefaultIfEmpty(0).ElementAtOrDefault(0)
} into final
select final;
LASTLY: I ran Ani's code snippet and confirmed that it ran successfully, so both approaches work and solve the original question.
I don't really understand the assumed equivalence between State and Suburb (where distinctSuburb == merge.State), but you can fix your query adding a .First() after the DefaultIfEmpty(0) call.
But here's how I would write your query: using a GroupJoin:
var results = from distinctSuburb in AllSupermarkets.Select(x => x.Suburb).Distinct()
join item in SomeSupermarkets
on distinctSuburb equals item.Suburb
into suburbGroup
select new
{
Suburb = distinctSuburb,
Count = suburbGroup.Count()
};
I have spent hours upon hours trying to figure out how to shape the data projected from linq to a strongly type view. My problem is I think my problem is I am unsure how to use IEnumberable and IGrouping.
Here is the linq:
var spec = from a in _entities.Approvals
join b in _entities.ApprovalSpecifications on a.HeaderlID equals b.HeaderlID into g
where a.ApprovalID == id
group a by a.HeaderlID into groupedByHeader
select new
{
Key = groupedByHeader.Key,
groupedByHeader
};
Can anyone suggest the method with which I should approach this? I am thinking a class for this would work best, but as I mentioned I'm not sure how to use IGrouping to build a class. Any help is appreciated!
Something like this?
class StronglyTypedGrouping {
public object Key { get; set; } // I can't infer Key type from the snippet.
public IEnumerable<Approval> Approvals { get; set; }
}
var spec = from a in _entities.Approvals
join b in _entities.ApprovalSpecifications on
a.HeaderlID equals b.HeaderlID into g
where a.ApprovalID == id
group a by a.HeaderlID into groupedByHeader
select new StronglyTypedGrouping {
Key = groupedByHeader.Key,
Approvals = groupedByHeader
};
I'm trying to get eager loading working with Subsonic, and it's been returning null for me.
In the method below, I'm trying to hydrate a domain model (UserModel) which contains another domain model (CompanyModel). However, with the code below, UserModel.Company is always null.
What am I missing here. Any help would be appreciated.
public IList<UserModel> GetUsers()
{
return (from u in SubsonicSqlServer.Users.All()
select new UserModel
{
UserId= u.UserId,
Company = (from c in u.Companies
select new CompanyModel
{
CompanyId = c.CompanyId,
CompanyName = c.CompanyName
}).SingleOrDefault(),
FirstName = u.FirstName,
LastName = u.LastName,
BirthDate = u.BirthDate
}).ToList();
}
Update (08/11/09):
More toying around with the code, I found out that setting CompanyId in the following example doesn't work either. I initially thought this was an issue with Subsonic, but if the code below doesn't work, I'm guessing it has something to do with my Linq statement. Any ideas?
public IList<UserModel> GetUsers()
{
return (from u in SubsonicSqlServer.Users.All()
select new UserModel
{
UserId= u.UserId,
CompanyId = Guid.NewGuid(),
FirstName = u.FirstName,
LastName = u.LastName,
BirthDate = u.BirthDate
}).ToList();
}
Update (11/17/2009):
Still haven't found a solution. But we are switching to nHibernate (not because of this issue).
"UserModel.Company is always null."
since you are setting this with an expression that ends with .SingleOrDefault(), I'm going to suggest that the query isn't returning a single item. Start investigating there. If you are expecting exactly one item in u.Companies, change to .Single() and force an early failure.
You can do the .Single() before creating the new CompanyModel object, I think.
As for style, I like the query comprehension syntax ("from x in y select") but find it awkward when combined with traditional dot-notation syntax. It's just hard to read. (LINQ - Fluent and Query Expression - Is there any benefit(s) of one over other?).
Consider using let in the query comprehension to make it clearer.
Also, since a query already returns an IEnumerable<T>, and calling ToList() forces all items to be realized, I would modify my method to return IEnumerable<T> if possible.
So, in your case, I would refactor the first to say:
public IEnumerable<User> GetUsers()
{
return from u in SubsonicSqlServer.Users.All()
let c = u.Companies.Single()
select new UserModel
{
UserId = u.UserId,
Company = new CompanyModel
{
CompanyId = c.CompanyId,
CompanyName = c.CompanyName
},
FirstName = e.FirstName,
LastName = e.LastName,
BirthDate = e.BirthDate
};
}
If it makes sense in your object model, you could modify User to have a constructor that takes whatever type u is, and it gets even simpler:
return from u in SubsonicSqlServer.Users.All()
select new UserModel (u);
or even
return SubsonicSqlServer.Users.All().Select(u => new UserModel (u));
Two things
You're returning a List<UserModel> when your method's signature line says IList<User> does UserModel inherit from User?
Am I missing something, where does e come from?
FirstName = e.FirstName,
LastName = e.LastName,
BirthDate = e.BirthDate Blockquote
Please check out my fork # github (http://github.com/funky81/SubSonic-3.0/commit/aa7a9c1b564b2667db7fbd41e09ab72f5d58dcdb) for this solution, actually there's a problem when subsonic try to project new type class, so there's nothin wrong with your code actually :D
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