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Linq check value in SQL table always is false

I tried to check if the cost or benefit value exists for the selected Id, then I will get the cost or benefit value from the table.
In the code below my if statement doesn't work and seems to always be false but the return benefit value works fine. Where is the problem?
public string GetCostBenefitAmount(int id)
{
if (db.CostBenefits.Any(c => c.ID == id && !c.Cost.Equals(0)))
{
return db.CostBenefits.Select(c => c.Cost).First().ToString();
}
return db.CostBenefits.Where(c=> c.ID == id).Select(c => c.Benefit).First().ToString();
}
This is my code in windows form for fill txtAmount textBox by GetCostBenefitAmount(int id) method:
var stockIdList = db.CostBenefitRepository.GetAllID();
int id = stockIdList[listBox.SelectedIndex];
CostBenefit costBenefit = db.GenericCostBenefitRepository.GetById(id);
txtStockName.Text = listBox.SelectedItem.ToString();
txtSoldAmount.Text = costBenefit.SoldAmount.ToString();
ComboCostBenefit.SelectedItem = db.CostBenefitRepository.GetCostBenefitOperation(id);
txtAmount.Text = db.CostBenefitRepository.GetCostBenefitAmount(id);

The Object.Equals method determines whether two object instances are equal. Try if (db.CostBenefits.Any(c => c.ID == id && c.Cost != 0)). For more info on the Object.Equals function see this post.
Edit:
As #Gert Arnold commented, the issue was in the return db.CostBenefits.Select(c => c.Cost).First().ToString(); where there was no filtering done before returning.

I think equals is only when you are using in a join. So just use
c.Cost != 0
instead.

New to programming how to make this code more concise

Hi this is my first question so apologies if it is really basic - I am very new to programming!!!
Using c# in MVC I am trying to select object which has a Date property from entitymodel context. This date then selects the relevant Weight object and so on to get my list of "Set" objects.
The code works and does what I want but would like some general guidance on how to make this code more concise. Here is the code:
public ActionResult showDiary(string datein)
{
LocalTestEntities1 dblists = new LocalTestEntities1();
DateTime date = Convert.ToDateTime(datein);
IEnumerable<ExerciseDiary> diary = from o in dblists.ExerciseDiaries where o.Date == date select o;
var mydiary = diary.ToList();
ExerciseDiary thediary = mydiary[0];
IQueryable<Weight> weights = from o in dblists.Weights where o.DiaryID == thediary.ID select o;
var selectedWeight = weights.ToList();
Weight weight = selectedWeight[0];
IEnumerable<Set> sets = from x in dblists.Sets where x.WeightId == weight.WeightID select x;
return View(sets);
}
It seems that I am taking too many steps here. I know that I am only returning one object to diary. Is there a way to get this object from dblists without sending to an IEnumerable?

Using the First() method will make things a little more concise:
public ActionResult showDiary(string datein)
{
using (LocalTestEntities1 dblists = new LocalTestEntities1())
{
DateTime date = Convert.ToDateTime(datein);
var thediary = (from o in dblists.ExerciseDiaries
where o.Date == date
select o).First();
var weight = (from o in dblists.Weights
where o.DiaryID == thediary.ID
select o).First();
var sets = (from x in dblists.Sets
where x.WeightId == weight.WeightID
select x).ToList();
}
return View(sets);
}
You should also wrap your LINQ to Entities data access in a using block so it's properly disposed of.

There's always many ways to do things, but... I think the easiest way would be to use First() since you are always just grabbing the first result in a list.
Another way to make it a little cleaner is to put your LINQ statements on multiple lines like I did for sets.
You can also use var, which some people like and others don't to have the compiler infer the type. I did this with sets below. I feel it cleans up the code a bit when you have large declarations with IEnumerable and generics.
public ActionResult showDiary(string datein)
{
LocalTestEntities1 dblists = new LocalTestEntities1();
DateTime date = Convert.ToDateTime(datein);
ExerciseDiary thediary = dblists.ExerciseDiaries.First(o => o.Date == date);
Weight weight = dblists.Weights.First(o.DiaryID == thediary.ID);
var sets = from x in dblists.Sets
where x.WeightId == weight.WeightID
select x;
return View(sets);
}
IMO this is easier to read than what you had in your answer above.

Be careful using First() because it will throw an exception if there are no records.

public ActionResult showDiary(string datein)
{
using( var dblists = new LocalTestEntities1())
{
var date = Convert.ToDateTime(datein);
var thediary = dblists.ExerciseDiaries.First(o => o.Date == date);
var weight = dblists.Weights.First(o => o.DiaryID ==thediary.ID);
var sets = dblists.Sets.Where(x => x.WeightId == weight.WeightID).AsEnumerable();
return View(sets);
}
}
Warning: If it's possible the data wont always be there. Use FirstOrDefault instead and check for null values.

How do I translate a linq query to an extension method chain with lambda expressions?

I'm using LINQ to Entities and I want to know how do I translate the following query to lambda expression using extension methods.
public _Deposito RegresaDepositosBancarios(int id)
{
return (from d in context.depositos_bancarios
where d.IDDeposito == id
select new _Deposito
{
idDeposito = d.IDDeposito,
cantidad = d.Monto,
fecha = d.FechaDeposito,
aplicado = d.Aplicado
}).Single();
}
Notice that I'm returning a _Deposito type, how do I achieve this using extension methods?
I need something like the following:
public Persona RegresaPersonaPorNombres(string nombres, string apellidoP, string apellidoM)
{
var p = context.personas.Where(x => x.Nombres == nombres &&
x.ApellidoP == apellidoP &&
x.ApellidoM == apellidoM).FirstOrDefault();
return p;
}
I don't want to return an entity type but a custom type instead

This is how this would be written with extension methods, but you really should not need to worry as they are both the same thing.
return context.depositos_bancarios
.Where(d=>d.IDDeposito == id)
.Select(d=>new _Deposito
{
idDeposito = d.IDDeposito,
cantidad = d.Monto,
fecha = d.FechaDeposito,
aplicado = d.Aplicado
})
.Single();
An interesting side note: I could have used a d=> in the Where and then an e=> in the Select. Whereas, the d propogates down throughout the phrase. The only way to reset it would be to use a let phrase. This has nothing to do with the direct question, but I just thought it interesting and wanted to point it out :)

LINQ query null exception when Where returns 0 rows

I have the following LINQ method that works as expected except if there are No Rows Found then I get a Null Exception. I am struggling on how I modify this to return 0 if that occurs.
public static int GetLastInvoiceNumber(int empNumber)
{
using (var context = new CmoDataContext(Settings.Default.LaCrosse_CMOConnectionString))
{
context.Log = Console.Out;
IQueryable<tblGreenSheet> tGreenSheet = context.GetTable<tblGreenSheet>();
return (tGreenSheet
.Where(gs => gs.InvoiceNumber.Substring(2, 4) == empNumber.ToString())
.DefaultIfEmpty()
.Max(gs => Convert.ToInt32(gs.InvoiceNumber.Substring(6, gs.InvoiceNumber.Length)))
);
}
}
Thanks
I tried one of Jon Skeet's suggestions, below, and now I get Unsupported overload used for query operator 'DefaultIfEmpty'
public static int GetLastInvoiceNumber(int empNumber)
{
using (var context = new CmoDataContext(Settings.Default.LaCrosse_CMOConnectionString))
{
context.Log = Console.Out;
IQueryable<tblGreenSheet> tGreenSheet = context.GetTable<tblGreenSheet>();
return tGreenSheet
.Where(gs => gs.InvoiceNumber.Substring(2, 4) == empNumber.ToString())
.Select(gs => Convert.ToInt32(gs.InvoiceNumber.Substring(6, gs.InvoiceNumber.Length)))
.DefaultIfEmpty(0)
.Max();
}
}

You're using
.Where(...)
.DefaultIfEmpty()
which means if there are no results, pretend it's a sequence with a single null result. You're then trying to use that null result in the Max call...
You can probably change it to:
return tGreenSheet.Where(gs => ...)
.Max(gs => (int?) Convert.ToInt32(...)) ?? 0;
This uses the overload finding the maximum of int? values - and it returns an int? null if there were no values. The ?? 0 then converts that null value to 0. At least, that's the LINQ to Objects behaviour... you'll have to check whether it gives the same result for you.
Of course, you don't need to use the ?? 0 if you're happy to change the method signature to return int? instead. That would give extra information, in that the caller could then tell the difference between "no data" and "some data with a maximum value of 0":
return tGreenSheet.Where(gs => ...)
.Max(gs => (int?) Convert.ToInt32(...));
Another option is to use the overload of DefaultIfEmpty() which takes a value - like this:
return tGreenSheet.Where(gs => ...)
.Select(gs => Convert.ToInt32(...))
.DefaultIfEmpty(0)
.Max();

In situations like this when there may or may not be a matching item, I prefer to return an object rather than a value type. If you return a value type, you have to have some semantics about what value means "there is nothing here." I would change it to return the last invoice, then (when it is non-null) get the invoice number from the invoice. Add a method to the class to return the numeric invoice number from the string.
public static tbleGreenSheet GetLastInvoice(int empNumber)
{
using (var context = new CmoDataContext(Settings.Default.LaCrosse_CMOConnectionString))
{
context.Log = Console.Out;
return context.GetTable<tblGreenSheet>()
.Where(gs => gs.InvoiceNumber.Substring(2, 4) == empNumber.ToString())
.OrderByDescending(gs => Convert.ToInt32(gs.InvoiceNumber.Substring(6, gs.InvoiceNumber.Length)))
.FirstOrDefault();
}
}
public class tbleGreenSheet
{
....
public int NumericInvoice
{
get { return Convert.ToInt32(InvoiceNumber.Substring(6, InvoiceNumber.Length)); }
}
...
}
Used as
var invoice = Foo.GetLastInvoice( 32 );
if (invoice != null)
{
var invoiceNumber = invoice.NumericInvoice;
...do something...
}
else
{
...do something else...
}

I had a remarkably similar experience with IQueryable<T> and NHibernate. My solution:
public static TExpr MaxOrDefault<TItem, TExpr>(this IQueryable<TItem> query,
Expression<Func<TItem, TExpr>> expression) {
return query.OrderByDescending(expression).Select(expression).FirstOrDefault();
}
The only drawback is that you are stuck with the standard default value, instead of getting to specify one.

Custom function in Entity Framework query sometimes translates properly, sometimes doesn't

I have this function:
public static IQueryable<Article> WhereArticleIsLive(this IQueryable<Article> q)
{
return q.Where(x =>
x != null
&& DateTime.UtcNow >= x.PublishTime
&& x.IsPublished
&& !x.IsDeleted);
}
And it works just fine in this query:
from a in Articles.WhereArticleIsLive()
where a.Id == 5
select new { a.Title }
But it doesn't work in this only slightly more complex query:
from s in Series
from a in Articles.WhereArticleIsLive()
where s.Id == a.SeriesId
select new { s, a }
I get this error message:
NotSupportedException: LINQ to Entities does not recognize the method 'System.Linq.IQueryable1[TheFraser.Data.Articles.Article] WhereArticleIsLive(System.Linq.IQueryable1[TheFraser.Data.Articles.Article])' method, and this method cannot be translated into a store expression.
Any idea why? Is there another way to consolidate query parameters like this?
Thanks in advance.

EDIT: corrections by Craig.
I'm leaving this here, because I think it's a valuable tool: Use linqkit! But not for solving this question though :-)
Instead of returning IQueryable, use Expression to factor out predicates. E.g. you could define the following static method on Article:
public static Expression<Func<Article,bool>> IsLive()
{
return x =>
x != null
&& DateTime.UtcNow >= x.PublishTime
&& x.IsPublished
&& !x.IsDeleted
}
Then, ensure to store a reference to this expression when building your query, something along the lines of (not tested):
var isLive = Article.IsLive();
from s in Series
from a in Articles.Where(isLive)
where s.Id == a.SeriesId
select new { s, a }