LINQ query with a WHERE clause with multiple conditions

Question

I use EntityFramework with POCOs.
Suppose I have POCOs defined like this (simplified):

class Class1
{
    public int ID;
    public int SomeNumber;
}

class          


        

Answer 1

According to your logic, if x.Class1 is not null, but x.Class1.SomeNumber is 3, it won't check all the other clauses.

If you want to check, if just some ClassN.SomeNumber == SomeNumber, then you should do it like this:

int SomeNumber = 1; // some number 
List<SomeClass> retValue = result 
    .Where(x => 
        { 
            if (x.Class1 != null && x.Class1.SomeNumber == SomeNumber) 
                return true;
            else if (x.Class2 != null && x.Class2.SomeNumber == SomeNumber) 
                return true;
            else if (x.Class3 != null && x.Class3.SomeNumber == SomeNumber) 
                return true;
            return false;
        }) 
    .ToList();

Answer 2

IMHO you should be OK with just this:

Database DB = new Database(); 
var result = DB.SomeClass.Where(x =>
                            Number == x.Class1.SomeNumber ||
                            Number == x.Class2.SomeNumber ||
                            Number == x.Class3.SomeNumber)
                         .ToList();

Your query loads all data and after that you evaluate condition in .NET = you must test null value prior to accessing SomeNumber but that is not needed if you evaluate SomeNumber in SQL through Linq-to-entities. Linq-to-entities should perform automatic null coalescing.