Develop Reference

ASP.NET MVC Linq Query DefaultIfEmpty not working [duplicate]

I have the following code. I'm getting error:
"The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type."
when CreditHistory table has no records.
var creditsSum = (from u in context.User
join ch in context.CreditHistory on u.ID equals ch.UserID
where u.ID == userID
select ch.Amount).Sum();
How can I modify the query to accept null values?

A linq-to-sql query isn't executed as code, but rather translated into SQL. Sometimes this is a "leaky abstraction" that yields unexpected behaviour.
One such case is null handling, where there can be unexpected nulls in different places. ...DefaultIfEmpty(0).Sum(0) can help in this (quite simple) case, where there might be no elements and sql's SUM returns null whereas c# expect 0.
A more general approach is to use ?? which will be translated to COALESCE whenever there is a risk that the generated SQL returns an unexpected null:
var creditsSum = (from u in context.User
join ch in context.CreditHistory on u.ID equals ch.UserID
where u.ID == userID
select (int?)ch.Amount).Sum() ?? 0;
This first casts to int? to tell the C# compiler that this expression can indeed return null, even though Sum() returns an int. Then we use the normal ?? operator to handle the null case.
Based on this answer, I wrote a blog post with details for both LINQ to SQL and LINQ to Entities.

To allow a nullable Amount field, just use the null coalescing operator to convert nulls to 0.
var creditsSum = (from u in context.User
join ch in context.CreditHistory on u.ID equals ch.UserID
where u.ID == userID
select ch.Amount ?? 0).Sum();

Had this error message when I was trying to select from a view.
The problem was the view recently had gained some new null rows (in SubscriberId column), and it had not been updated in EDMX (EF database first).
The column had to be Nullable type for it to work.
var dealer = Context.Dealers.Where(x => x.dealerCode == dealerCode).FirstOrDefault();
Before view refresh:
public int SubscriberId { get; set; }
After view refresh:
public Nullable<int> SubscriberId { get; set; }
Deleting and adding the view back in EDMX worked.
Hope it helps someone.

I have used this code and it responds correctly, only the output value is nullable.
var packesCount = await botContext.Sales.Where(s => s.CustomerId == cust.CustomerId && s.Validated)
.SumAsync(s => (int?)s.PackesCount);
if(packesCount != null)
{
// your code
}
else
{
// your code
}

You are using aggregate function which not getting the items to perform action , you must verify linq query is giving some result as below:
var maxOrderLevel =sdv.Any()? sdv.Max(s => s.nOrderLevel):0

I see that this question is already answered. But if you want it to be split into two statements, following may be considered.
var credits = from u in context.User
join ch in context.CreditHistory
on u.ID equals ch.UserID
where u.ID == userID
select ch;
var creditSum= credits.Sum(x => (int?)x.Amount) ?? 0;

Got this error in Entity Framework 6 with this code at runtime:
var fileEventsSum = db.ImportInformations.Sum(x => x.FileEvents)
Update from LeandroSoares:
Use this for single execution:
var fileEventsSum = db.ImportInformations.Sum(x => (int?)x.FileEvents) ?? 0
Original:
Changed to this and then it worked:
var fileEventsSum = db.ImportInformations.Any() ? db.ImportInformations.Sum(x => x.FileEvents) : 0;

I was also facing the same problem and solved through making column as nullable using "?" operator.
Sequnce = db.mstquestionbanks.Where(x => x.IsDeleted == false && x.OrignalFormID == OriginalFormIDint).Select(x=><b>(int?)x.Sequence</b>).Max().ToString();
Sometimes null is returned.

Conditional where clause with date parameters raises a has no supported translation to SQL. error in Linq to SQL with C#

I'm working on a linq to sql project using Visual C# 2008 and dot Net framework 4.5.
my query is as follows
var q =
from a in dc.GetTable<invoice_in>()
join b in dc.GetTable<supplier>()
on a.supplier_id equals b.id
where a.invoice_date >= date_from
select new Invoice_in(a.id, a.amount ?? 0, a.invoice_number ,
a.supplier_id ?? 0, a.supplier.s_name,
a.invoice_date ?? System.DateTime.Today);
invoce_in is a linq class while Invoice_in is a class I defined with a similar structure.
When I put the date comparison inside where clause within the last query, everything is OK. But I need to use a conditional where, as the query parameters goes after the main query clause
I added the following lines to the previous code
if (date_from != null)
{
q = q.Where(w => w.invoice_date >= date_from);
}
Where w.invoice_date is of DateTime type and it is data member of the class Invoice_in (defined by me).
Adding that last lines of code causes the following runtime error:
"has no supported translation to SQL"
I've tried dozens of methods on the web such as using SQLMethods for comparing dates and such stuff, nothing works
Please Help... Thanks in advance...

This should work for you:
var q =
from a in dc.GetTable<invoice_in>()
join b in dc.GetTable<supplier>()
on a.supplier_id equals b.id
select a;
//since you compared date_from against null I assume it is Nullable<DateTime>
if (date_from.HasValue)
{
q = q.Where(a => a.invoice_date >= date_from.Value);
}
var result =
q.Select(a => new Invoice_in(a.id, a.amount ?? 0,
a.invoice_number ,
a.supplier_id ?? 0,
a.supplier.s_name,
a.invoice_date ?? System.DateTime.Today))
.ToList();

Dynamic where clause in LINQ?

I am trying to load data based on Dynamic where condition.
string tempQry = string.Empty;
if (!string.IsNullOrEmpty(cusid) && !string.IsNullOrEmpty(mktid))
tempQry = "x=>x.MarketID==" + mktid + "&& x.MasterCustomerID==" + cusid;
if (string.IsNullOrEmpty(cusid))
tempQry = "x=>x.MarketID==" + mktid;
if (string.IsNullOrEmpty(mktid))
tempQry = "x=>x.MasterCustomerID==" + cusid;
_lstOptInInterest = new LinkedList<OptInInterestArea>(
(from a in _lstOptInInterest
join b in _marketoEntities.CustCommPreferences.Where(tempQry)
on new { CODE = a.Code, SUBCODE = a.SubCode } equals new { CODE = b.Option_Short_Name, SUBCODE = b.Option_Short_Subname }
into leftGroup
from b in leftGroup.DefaultIfEmpty()
select new OptInInterestArea()
{
Code = a.Code,
SubCode = a.SubCode,
SubCodeDescription = a.SubCodeDescription,
CodeDescription = a.CodeDescription,
PrevOptIn = b != null && b.OptedIn == true
}).ToList());
It is giving compilation error Where(tempQry).
'System.Data.Entity.DbSet<Market.Data.CustCommPreference>' does not contain a definition for 'Where' and the best extension method overload 'System.Linq.Queryable.Where<TSource>(System.Linq.IQueryable<TSource>, System.Linq.Expressions.Expression<System.Func<TSource,bool>>)' has some invalid arguments
How to handle this?

Where awaits conditions in form of lambdas rather than strings, so you have to refactor your code a little bit (just an idea below):
IQueryable<CustCommPreference> query = _marketoEntities.CustCommPreferences.AsQueryable();
if (!string.IsNullOrEmpty(cusid))
query = query.Where(x => x.MasterCustomerID == cusid);
if (!string.IsNullOrEmpty(mktid))
query = query.Where(x => x.MarketID == mktid);
and later use it:
...
join b in query
...

see this blog by Scott. It should help you sort your issue

The error you are seeing appears to indicate that you are using EF not LINQ to SQL. Please correct your tags if that is the case. If you want to use strings, consider using ObjectQuery's Where method instead of using DBSet. Alternatively, you could build the entire query using EntitySQL.

LINQ join on columns AND nullable variable

I am trying to join tables using LINQ by matching columns where a column in the joined table is equal to a variable or the variable is null (at which point the join still needs to happen just not on that field).
My LINQ is something like:
var data = (
from lt in cxt.CmsPageRow
join page in cxt.CmsPage on new { lt.CmsPageID, cmsSiteID.Value } equals new { page.CmsPageID, page.CmsSiteID }
...
cmsSiteID is a nullable INT.
I cannot compile my code as it is complaining about "Type inference failed in the call to 'Join'."
On top of that I need to only join on page.CmsSiteID when cmsSiteID is not null. If cmsSiteID is null then the join on lt.CmsPageID still needs to happen.
* EDIT *
The question has kind of changed now. I can get it to do what I want by using a WHERE clause on the join in my LINQ.
join page in cxt.CmsPage.Where(p=>(cmsSiteID==0||p.CmsSiteID==cmsSiteID)) on lt.CmsPageID equals page.CmsPageID
However, this still runs slow. If I change the parameter passed through to a literal it executes instantly.
Slow runner
(#p__linq__1 = 0 OR [Extent2].[CmsSiteID] = #p__linq__1)
Fast runner
(267 = 0 OR [Extent2].[CmsSiteID] = 267)
Is there a way to speed this up?

join in LINQ assumes an inner join (no nulls). Try pulling the null stuff out into separate where clauses. I think something along these lines should work for what you're describing.
from lt in cxt.CmsPageRow
join page in cxt.CmsPage on lt.CmsPageID == page.CmsPageID
where cmsSiteID == null ||
(cmsSiteID != null && (page.CmsSiteID == null || page.CmsSiteId == cmsSiteID.Value))
select ...
Update
I didn't realize that performance was an issue for you. In that case, I'd suggest creating a different query structure based on values that are known at run-time and don't depend on individual rows:
var rows =
from lt in cxt.CmsPageRow
join page in cxt.CmsPage on lt.CmsPageID == page.CmsPageID
select new {lt, page};
if (cmsSiteID != null)
{
rows = rows.Where(r => r.page.CmsSiteID == null ||
r.page.CmsSiteId == cmsSiteID.Value));
}
var data = rows.Select(...);
Also, if your data context is set up right, you should be able to use navigation properties to simplify your code somewhat.
var rows = ctx.CmsPageRow;
if (cmsSiteID != null)
{
rows = rows.Where(r => r.CmsPage.Any(p => p.CmsSiteID == null ||
p.CmsSiteId == cmsSiteID.Value));
}
var data = rows.Select(...);

"IN" Operator in Linq

I am trying to convert an old raw Sql query in Linq with Entity Framework here.
It was using the IN operator with a collection of items. The query was something like that:
SELECT Members.Name
FROM Members
WHERE Members.ID IN ( SELECT DISTINCT ManufacturerID FROM Products WHERE Active = 1)
ORDER BY Members.Name ASC
Since the return of the subquery is not a single string but a collection of strings I can't use the String.Contains() method.
I thought about doing something like :
var activeProducts = (
from products in db.ProductSet
where product.Active == true
select product.ManufacturerID);
and then
var activeMembers = (
from member in db.ContactSet
where member.ID.ToString().Contains(activeProducts));
but it stops at the contains saying it has invalid arguments ... I can't select activeProducts.ManufacturerID because obviously the proprety is not there since it returns an IQueryable...
Bottom line what I'm trying to do here is to return a list of members who have at least one active product.
Any hint ?
[edit]
Here's the full query code ... I tried with the contains on the second expression, Linq didn't seem to like it :
Server Error in '/' Application.
LINQ to Entities does not recognize the method 'Boolean Contains[String](System.Linq.IQueryable``1[System.String], System.String)' method, and this method cannot be translated into a store expression.
var activeProduct =(from product in Master.DataContext.ProductSet
where product.Active == true
&& product.ShowOnWebSite == true
&& product.AvailableDate <= DateTime.Today
&& ( product.DiscontinuationDate == null || product.DiscontinuationDate >= DateTime.Today )
select product.ManufacturerID.ToString() );
var activeArtists = from artist in Master.DataContext.ContactSet
where activeProduct.Contains(artist.ID.ToString())
select artist;
NumberOfArtists = activeArtists.Count();
artistsRepeater.DataSource = activeArtists;
artistsRepeater.DataBind();
[More details]
ManufacturerID is a nullable GUID apparently...
For some reason the ContactSet class do not contain any reference to the products I guess I will have to do a join query, no clues here.

var activeMembers = (
from member in db.ContactSet
where activeProducts.Select(x=>x.ID).Contains(member.ID));

Try where activeProducts.Contains(member.ID).
EDIT: Did you try it without any ToStrings?

You can do it in one query:
var q = from member in db.ContactSet
where member.Products.Any(p => p.IsActive)
select member;

Try the solution posted by Colin Meek at: http://social.msdn.microsoft.com/forums/en-US/adodotnetentityframework/thread/095745fe-dcf0-4142-b684-b7e4a1ab59f0/. It worked for me.

What about this:
from m in members
where products.FirstOrDefault(prod => prod.IsActive == 1 && prod.Id == m.Id) != null
select m;
you can chain any number of conditions required in the where clause using &&
Ash..

from m in members
where products.Any(p => p.Active && p.ManufacturerID == m.ID)
select m
or
from m in members
join p in products on m.ID equals p.ManufacturerID
where p.Active
select m

Instead of this:
var activeMembers = (
from member in db.ContactSet
where member.ID.ToString().Contains(activeProducts));
Try this:
var activeMembers = (
from member in db.ContactSet
where activeProducts.Contains(member.ID));

What if you swap the statement (untested)?
where activeProducts.Contains(member.ID)

How about this...
var activeProducts = (
from products in db.ProductSet
where product.Active == true
select product.ManufacturerID);
var activeMembers = (
from member in db.ContactSet
where activeProducts.Contains(member.ID.ToString()));

A helper or extension method will work fine when querying against objects in memory. But against an SQL database, your LINQ code will be compiled into an expression tree, analysed and translated into an SQL command. This functionality has no concept of custom-made extension methods or methods of other objects like .Contains(...).
It could be easily implemented into the standard LINQ-To-SQL functionality by Microsoft though. But as long as they don't want, we're helpless as long it's not an open source functionality.
All you can do is create your own QueryProvider that goes against an SQL database. But it will be hard and it would be only for that one in feature alone that you're missing.
However, if you really wanna go that route, have fun: LINQ: BUILDING AN IQUERYABLE PROVIDER SERIES

Finally I managed to code something really ugly, but that actually works! (lol)
var activeProduct =(from product in Master.DataContext.ProductSet
where product.Active == true
&& product.ShowOnWebSite == true
&& product.AvailableDate <= DateTime.Today
&& ( product.DiscontinuationDate == null || product.DiscontinuationDate >= DateTime.Today )
select product.ManufacturerID ).Distinct();
var artists = from artist in Master.DataContext.ContactSet
select artist;
List<Evolution.API.Contact> activeArtists = new List<Evolution.API.Contact>();
foreach (var artist in artists)
{
foreach(var product in activeProduct)
{
if (product.HasValue && product.Value == artist.ID)
activeArtists.Add(artist);
}
}
NumberOfArtists = activeArtists.Count();
artistsRepeater.DataSource = activeArtists;
artistsRepeater.DataBind();

I have already posted about the same at
http://www.codeproject.com/Tips/336253/Filtering-records-from-List-based-similar-to-Sql-I

var q = (from p in db.DOCAuditTrails
where p.ActionUser == "MyUserID"
&& p.ActionTaken == "Not Actioned"
&& p.ActionDate > DateTime.Parse("2011-09-13")
select p.RequisitionId).Distinct();
var DocAuditResults = db.DOCAuditTrails.Where(p
=> q.ToArray().Contains(p.RequisitionId));

Without know the exact mappings it is hard to tell what can be done and what can't. I will assume that there isn't any casting involved. Firstly you have to remember that everything in the Linq Expression tree must have an equivalent in SQL. As some others have noted, you have a object.ToString() in your Linq Statements.
However it seems that what people have neglected to mention is that you have TWO usages of object.ToSting(), both of which must be removed.
I would also make an extra variable to change the closure's capture type to be explicitly of DataContext (since the Linq statement is like a lambda, and delayed evaluated. It will need to take the whole of the Master variable. Earlier I stated that everything in your Linq must have an equivalent in SQL. Given that Master can't possibly exist in SQL, there is no DataContext property/column/mapping for the type of Master).
var context = Master.DataContext;
var activeProduct = from product in context.ProductSet
where product.Active == true
&& product.ShowOnWebSite == true
&& product.AvailableDate <= DateTime.Today
&& ( product.DiscontinuationDate == null || product.DiscontinuationDate >= DateTime.Today )
select product.ManufacturerID;
var activeArtists = from artist in context.ContactSet
where activeProduct.Contains(artist.ID)
select artist;
I hope the above changes work for you.
In many cases issues with Linq to ORMs can be traced back to your Linq Expression capturing a non primative (DateTime, int, string etc) and non ORM based class (DataContext/EntityObject etc). The other major gotcha is usage of functions and operators that aren't exposed by the ORM (it is possible to map user defined functions to .net function through the ORM, but I would not recommend it due to indexing issues).