Develop Reference

Multiple Checkbox create LINQ

I have 4 checkboxes and based on which ones the user clicks on, I need to produce the LINQ statement. As mentioned below in the comment section, if I select just one checkbox, it works fine. If I select multiple checkboxes, it returns 0 results.
The 4 checkboxes are 1) "Item1" 2) "Item2" 3) "Item3" 4) "Item4".
This is what I have far:
var entity = _w_ItemRepository.GetMany(p => p.ID == id);
/* If I select just one item it works fine. If I select multiple items get 0 result */
entity = entity.Where
(p => (p.ItemType == 1 || !item1)
&& (p.ItemType == 2 || !item2)
&& (p.ItemType == 2 || !item3)
&& (p.ItemType == 3 || !item4)
);

I suspect the &&s need to be ||s. Consider if both item1 and item2 are true then you're essentially saying:
.Where(p => p.ItemType == 1 && p.ItemType == 2)
When the intent is probably:
.Where(p => p.ItemType == 1 || p.ItemType == 2)
(It also looks like there's a typo, you specify ItemType == 2 twice.)
Try:
entity = entity.Where
(p => (p.ItemType == 1 || !item1)
|| (p.ItemType == 2 || !item2)
|| (p.ItemType == 3 || !item3)
|| (p.ItemType == 4 || !item4)
);
Or I think this may be more clear, adding each clause if itemX is true:
entity = entity.Where
(p => (item1 && p.ItemType == 1)
|| (item2 && p.ItemType == 2)
|| (item3 && p.ItemType == 3)
|| (item4 && p.ItemType == 4)
);

Multiple using of || and && operands

I have a query using Entity Framework. It has many different operands and I am confused with its priority. I am getting the wrong result. I need all records that IsPaid == true or IsPaid == null, also all records must be TypeId == 1 or TypeId == 2, also must be CityId == 1 and CategoryId == 2. For some reason it doesn't evaluate CityId and CategoryId.
What am I doing wrong? Thanks.
var list = db.Ads.Where (x =>
x.IsPaid == true || x.IsPaid == null &&
x.TypeId == 1 || x.TypeId == 2 &&
x.CityId == 1 && x.CategoryId == 2
).ToList();

The best way to solve this problem is using brackets.
You should always use them even if you know the binding prioritys, to increase readability of your code.
(x.IsPaid == true || x.IsPaid == null) && (x.TypeId == 1 || x.TypeId == 2) && x.CityId == 1 && x.CategoryId == 2
&& has a higher proirity than ||
So false && false || true would be translated to (false && false) || true => true
Sidenote as mentioned by #Joey:
Instead of (x.IsPaid == true || x.IsPaid == null) you can write (x.IsPaid != false).

Due to operator precedence, && binds higher than ||.
If you chain Where statements, it's more clear what happens:
var list = db.Ads
.Where(x => x.IsPaid == true || x.IsPaid == null)
.Where(x=> x.TypeId == 1 || x.TypeId == 2)
.Where(x=> x.CityId == 1)
.Where(x=> x.CategoryId == 2)
.ToList();

&& has a higher precedence than ||, just like in math. So, effectively your condition is the following:
x.IsPaid == true ||
x.IsPaid == null && x.TypeId == 1 ||
x.TypeId == 2 && x.CityId == 1 && x.CategoryId == 2
If any of those expressions on separate lines are true, the whole expression is true. You have to use parentheses to clarify here:
(x.IsPaid == true || x.IsPaid == null) &&
(x.TypeId == 1 || x.TypeId == 2) &&
x.CityId == 1 &&
x.CategoryId == 2

Try this:
var list = db.Ads.Where (
(x => x.IsPaid == true || x.IsPaid == null) &&
(x.TypeId == 1 || x.TypeId == 2) &&
(x.CityId == 1 && x.CategoryId == 2)
).ToList();

Linq opening and closing parentheses does not match

I have this code:
using (Entities db = new Entities())
{
refer = db.Refferals.Where(r =>
r.RefferalDetails.Any(rd =>
(Name.Contains(rd.Name) || rd.Name.Contains(Name) || LastName.Contains(rd.LastName) || rd.LastName.Contains(LastName)
|| Company.Contains(r.Company) || r.Company.Contains(Company)
Mobile.Contains(rd.Mobile) || rd.Mobile.Contains(Mobile))) &&
Mobile.Length > 9 && Name.Length > 1 && LastName.Length > 1 && Company.Length > 2
).ToArray();
}
Although the parentheses count is correct but the editor offers that there is one extra parantheses.
I tried restarting Visual Studio but its the same.

Try adding the missing || between r.Company.Contains(Company) and Mobile.Contains(rd.Mobile).
And fix the indenting, that makes it much easier to see what's wrong. When I indented it, the missing operator stuck out like a sore thumb, and it's easy to see how the parens work.
using (Entities db = new Entities())
{
refer = db.Refferals.Where(r =>
r.RefferalDetails.Any(rd =>
(
Name.Contains(rd.Name)
|| rd.Name.Contains(Name)
|| LastName.Contains(rd.LastName)
|| rd.LastName.Contains(LastName)
|| Company.Contains(r.Company)
|| r.Company.Contains(Company)
|| /* <-- ADDED OR OPERATOR HERE */
Mobile.Contains(rd.Mobile)
|| rd.Mobile.Contains(Mobile)
)
)
&& Mobile.Length > 9
&& Name.Length > 1
&& LastName.Length > 1
&& Company.Length > 2
).ToArray();
}

It's missing one**||** before Mobile.Contains(rd.Mobile)
refer = db.Refferals.Where
(
r => r.RefferalDetails.Any
(
rd =>
(
Name.Contains(rd.Name) || rd.Name.Contains(Name) || LastName.Contains(rd.LastName) || rd.LastName.Contains(LastName)
|| Company.Contains(r.Company) || r.Company.Contains(Company)
|| Mobile.Contains(rd.Mobile) || rd.Mobile.Contains(Mobile)
)
)
&& Mobile.Length > 9 && Name.Length > 1 && LastName.Length > 1 && Company.Length > 2
).ToArray();

Without running code it seems you do some kind of unary selections (rd). I would suggest you start refactoring your code and break out each condition a part...

Not understanding LINQ query

I am maintaining a project and have come across some code which I can't understand. LINQ query:
var toDraw = from tile in testArr.AsEnumerable()
where tile.Item_Business_Unit != null ?
((tile.Ending_Date >= DateTime.Now || tile.Ending_Date == DateTime.MinValue) &&
((tile.Sales_Code == null) || (tile.Sales_Code.ToString() == customerNumber) ||
(tile.Sales_Code.ToString() == cpg)) && (tile.Unit_Price != 0)) :
((tile.Ending_Date >= DateTime.Now || tile.Ending_Date == DateTime.MinValue) &&
((tile.Sales_Code == null) || (tile.Sales_Code.ToString() == customerNumber) ||
(tile.Sales_Code.ToString() == cpg)) && (tile.Unit_Price != 0))
select tile;
From what I understand, from an array a tile is being selected which has the following criteria:
Ending date can be datetime.now or datetime.minvalue
Sales code can be null or can be equal to customer no or cpg
Unit price should be greater than 0
But I am not understanding why there is a conditional expression after tile.Item_Business_Unit since both of the conditions perform the same thing. So will the item be selected even if it has a null business unit? And does this work different from normal if/else operations?
Any suggestions would be very appreciated.

Are you being thrown by the shortcut notation?
x = (test_case) ? (true_part) : (false_part);
If test_case evaluates to true, you would have
Whereas if test_case evaluates to false, this expression would be evaluated
UPDATE:
As an FYI: The resulting test of both sides of that conditional expression above are equal, so that cryptic code is not even necessary.
You could replace that with this:
var toDraw = from tile in testArr.AsEnumerable()
where
((tile.Ending_Date >= DateTime.Now || tile.Ending_Date == DateTime.MinValue) &&
((tile.Sales_Code == null) || (tile.Sales_Code.ToString() == customerNumber) || (tile.Sales_Code.ToString() == cpg)) &&
(tile.Unit_Price != 0))
select tile;

Why is my query not returning anything

I was writing a LINQ query to filter the records based on user input and selection. Some of the inputs may not be given from the user. So i need to filter based on the given input. I tried giving value for only 1 out of 5 optional inputs. But the query is not returning anything. Please help me to find the proper query. you can better understand after seeing the query.
Code
var model = (from items in Db.Items
where ((items.ItemNo == null ||
items.ItemNo == String.Empty) ||
((items.ItemNo.CompareTo(DD.FromItemNo) >= 0) &&
(items.ItemNo.CompareTo(DD.ToItemNo) <= 0))) &&
(items.InfoTypeId == 0 ||
(items.InfoTypeId == DD.InfoType)) &&
(items.CreatedOn == null ||
(items.CreatedOn >= DD.Start &&
items.CreatedOn <= DD.End)) &&
(items.StatusId == 0 ||
(items.StatusId == DD.Status)) &&
(items.LocationId == 0 ||
(items.LocationId == DD.Location)) &&
(items.CollectionId == 0 ||
(items.CollectionId == DD.Collection))
select new ViewModel()
{
Itemid = items.Id,
INo = items.ItemNo,
BTags = (from asd in Db.BibContents
where asd.BibId == items.BibId &&
asd.TagNo == "245" &&
asd.Sfld == "a"
select asd.Value).FirstOrDefault(),
Sid = (from stat in Db.ItemStatus1
where stat.Id == items.StatusId
select stat.Description).FirstOrDefault(),
Option = DD.Option,
CurrItemNo = DD.ItemNumber
}).ToList();

You've got to check the values of DD for nulls or 0s, not those of items:
var model = (from items in Db.Items
where
(
(DD.ItemNo == null || DD.ItemNo == String.Empty)
|| (items.ItemNo.CompareTo(DD.FromItemNo) >= 0 && items.ItemNo.CompareTo(DD.ToItemNo) <= 0)
)
&& (DD.InfoTypeId == 0 || (items.InfoTypeId == DD.InfoType))
&& (DD.CreatedOn == null || (items.CreatedOn >= DD.Start && items.CreatedOn <= DD.End))
&& (DD.StatusId == 0 || (items.StatusId == DD.Status))
&& (DD.LocationId == 0 || (items.LocationId == DD.Location))
&& (DD.CollectionId == 0 || (items.CollectionId == DD.Collection))
select ...