how to find non null or string.empty columns using linq?

Question

here's my code. it works

var someField = "abc";

var list = Entities.Where(x=>SomeField).FirstOrDefault();

here's the problem, someField can also be null or string.empty. If someField is null or string.empty, I will select everything where SomeField is null or string.empty.

var list = Entities.Where(x=>SomeField  == null || SomeField == string.empty).FirstOrDefault();

right now, I have an if else statement to check if someField has value,then decided which query to use.

I need to combine the 2 queries into one. because if there are fields we need to check, then this if else statemetn will get very long.

In the first snippet you've implied that SomeField is of type bool. Now it's of type string? Your question is very unclear. — Jon Skeet
– Jon Skeet, Commented Oct 24, 2012 at 16:31

Jon Skeet · Accepted Answer · 2012-10-24 16:33:49Z

3

I suspect you actually want to match x.SomeField == someField, or everything if someField is null or empty, right?

I would do this:

var fetchAll = string.IsNullOrEmpty(someField);
var list = Entities.FirstOrDefault(x => fetchAll || x.SomeField == someField);

You can inline it, but I think the above is clearer than checking whether someField is null or empty within the query.

Note that I've used the overload of FirstOrDefault which takes a predicate - this is equivalent to using Where followed by FirstOrDefault, but a bit more concise.

answered Oct 24, 2012 at 16:33

Jon Skeet

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1 Comment

lc. Over a year ago

Hmm, interesting. I suspect this is a more correct interpretation of the OP's intent.

luis_laurent · Accepted Answer · 2012-10-24 16:44:11Z

1

I did a little sample, I'm just getting the entity with a null or empty value in SomeField...

I hope this works for you.

public class MyEntity
{
    public int ID { get; set; }

    public string SomeField { get; set; }
}

static void Main(string[] args)
{
   List<MyEntity> Entities = new List<MyEntity>();
   for (int i = 0; i < 10; i++)
   {
       Entities.Add(new MyEntity()
                   {
                       ID = i,
                       SomeField = "Value " + i.ToString()
                   });
   }

   Entities.Add(new MyEntity() { ID = 10, SomeField = null });
   var entity = Entities.Where(x => string.IsNullOrEmpty(x.SomeField)).FirstOrDefault();
}

answered Oct 24, 2012 at 16:44

luis_laurent

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