Dealing with Null values in a database when using linq.

Posted on 2014-02-18
Last Modified: 2016-02-10
I have a list of cost centers that I want to grab. My DB Admin allows nulls for one of my fields. I can't seem to get around this. What can I do?? How do I get around this? Right now my error is "Unable to cast the type 'System.Nullable`1' to type 'System.Object'. LINQ to Entities only supports casting EDM primitive or enumeration types."

    public class CostCenter
        public string DepartmentID { get; set; }
        public string ModelName { get; set; }

List<CostCenter> DList = new List<CostCenter>();
                DList = (from x in ctx.Inventory where x.CostCenterID != null
                         select new CostCenter { ModelName = x.CostCenterID + "-" + x.ModelName, DepartmentID = SqlFunctions.StringConvert((double)(x.CostCenterID ?? 1)) }).Distinct().ToList();

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Question by:NickMalloy
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LVL 21

Expert Comment

by:Craig Wagner
ID: 39868036
I'm assuming the CostCenterID is the column that allows null? I'm not sure why you're having any trouble with it because your "where" clause eliminates any rows where the CostCenterID is null.

What is the actual datatype of CostCenterID in the database? Your casting and conversions in the Select seem entirely unnecessary. You've already eliminated any row where the CostCenterID is null, so why is the null coalesce (i.e. ??) necessary?

Author Comment

ID: 39868722
I started going down that route because of the traditional can't convert ?int to int.
LVL 21

Expert Comment

by:Craig Wagner
ID: 39868851
I'm afraid that doesn't give me enough information to provide any further assistance. If you still need help please see the rest of my questions from the first post and provide answers. Thanks.
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Expert Comment

ID: 39869993
If the CostCenterID is an numeric datatype, then you need to use:

where x.CostCenterID.HasValue

Author Comment

ID: 39870427
I'm trying to get ride of the error.

cannot implicitly convert type 'int? ' to 'int'

I've tried several ways, but don't know how to get around it. CostCenterID allows nulls.

Current Code

List<CostCenter> DList = new List<CostCenter>();
DList = (from x in ctx.Inventory where x.CostCenterID.HasValue
                         select new CostCenter { ModelName = x.CostCenterID + "-" + x.ModelName, DepartmentID = x.CostCenterID }).Distinct().ToList();

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Accepted Solution

DaveKeyes earned 500 total points
ID: 39873844
Use the following to retrieve the value from a nullable int:

ModelName = x.CostCenterID.Value

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