What is the linq equivalent to the SQL IN operator

Question

With linq I have to check if a value of a row is present in an array.
The equivalent of the sql query:

WHERE ID IN (2,3,4,5)

How can I

Answer 1

An IEnumerable<T>.Contains(T) statement should do what you're looking for.

Answer 2

Perform the equivalent of an SQL IN with IEnumerable.Contains().

var idlist = new int[] { 2, 3, 4, 5 };

var result = from x in source
          where idlist.Contains(x.Id)
          select x;

Answer 3

A very basic example using .Contains()

List<int> list = new List<int>();
for (int k = 1; k < 10; k++)
{
    list.Add(k);
}

int[] conditionList = new int[]{2,3,4};

var a = (from test in list
         where conditionList.Contains(test)
         select test);

Answer 4

db.SomeTable.Where(x => new[] {2,3,4,5}.Contains(x));

or

from x in db.SomeTable
where new[] {2,3,4,5}.Contains(x)

Answer 5

Following is a generic extension method that can be used to search a value within a list of values:

    public static bool In<T>(this T searchValue, params T[] valuesToSearch)
    {
        if (valuesToSearch == null)
            return false;
        for (int i = 0; i < valuesToSearch.Length; i++)
            if (searchValue.Equals(valuesToSearch[i]))
                return true;

        return false;
    }

This can be used as:

int i = 5;
i.In(45, 44, 5, 234); // Returns true

string s = "test";
s.In("aa", "b", "c"); // Returns false

This is handy in conditional statements.

Answer 6

Intersect and Except are a little more concise and will probably be a bit faster too.

IN

collection.Intersect(new[] {2,3,4,5});

NOT IN

collection.Except(new[] {2,3,4,5});

or

Method syntax for IN

collection.Where(x => new[] {2,3,4,5}.Contains(x));

and NOT IN

collection.Where(x => !(new[] {2,3,4,5}.Contains(x)));