Is there a C# IN operator?

Question

In SQL, you can use the following syntax:

SELECT *
FROM MY_TABLE
WHERE VALUE_1 IN (1, 2, 3)

Is there an equivalent in C#? The IDE seems to

Answer 1

Common, LINQ way more powerful:

var list = new List<string> { "Tomato", "Orange", "Mango"};
var query = from i in my_table
            from v in list
            where i.Name.StartsWith(v)
            select i;

Answer 2

Duplicate of : LINQ to SQL in and not in

select * from table where fieldname in ('val1', 'val2') 

or

select * from table where fieldname not in (1, 2) 

The equivalent of IN and NOT IN queries in LINQ to SQL would be something like this:

List<string> validValues = new List<string>() { "val1", "val2"}; 
var qry = from item in dataContext.TableName 
          where validValues.Contains(item.FieldName) 
          select item; 

and this:

List<int> validValues = new List<int>() { 1, 2}; 
var qry = from item in dataContext.TableName 
          where !validValues.Contains(item.FieldName) 
          select item; 

Answer 3

There is no in operator that looks for a value in a collection, instead it's a method of the collection, called Contains.

The most scalable solution is to use a HashSet as the collection. Checking for a value in a HashSet is close to an O(1) operation, compared to doing it in a List where it is an O(n) operation. That means that you can pack a lot of values in a HashSet and it's still fast, while looking for a value in a List gets slower the more values you have.

Example:

var set = new HashSet<int>();
set.Add(1);
set.Add(2);
set.Add(3);

var result = items.Select(i => set.Contains(i.value));

Answer 4

I agree the best way to implement the In operator is with an Extension Method. I did it a little differently:

public static bool In(this string str, string CommaDelimintedStringSet)
{
    string[] Values = CommaDelimintedStringSet.Split(new char[] { ',' });
    foreach (string V in Values)
    {
       if (str == V)
         return true;
    }
    return false;
}

The difference is that you don't have to put quotes around each value, only the entire set of comma delimited values, which is easier to type:

bool result = MyString.In("Val1,Val2,Val3");

Answer 5

There's no "in" operator in C#, the "in" keyword is used only with "foreach (... in ...)" or "from ... in ...".

The LINQ equivalent of your SQL query would be:

List<int> list = new List<int> { 1, 2, 3 };
var query = from row in my_table
            where list.Contains(row.value1)
            select row;

Answer 6

I do something like this:

var shippingAddress = checkoutContext.Addresses.Where(a => (new HashSet<AddressType> { AddressType.SHIPPING_ONLY, AddressType.BILLING_AND_SHIPPING }).Contains(a.AddressType) && a.Id == long.Parse(orderDto.ShippingAddressId)).FirstOrDefault();