How to Use Contains() with a String Array in LINQ Queries?

How to Replace Contains(string) with Contains(string[]) in LINQ Queries

In LINQ, the Contains() method can be used to check if a collection contains a specific element. By default, the Contains() method takes a single string parameter, but what if you need to compare against an array of strings?

Question:

I have a LINQ query that looks like this:

from xx in table
where xx.uid.ToString().Contains(string[])
select xx

The values in the string[] array are numbers (e.g., 1, 45, 20, 10). I want to use the Contains() method to check if the xx.uid property (which is a number) is present in the array. How can I do this?

Answer:

To compare xx.uid against an array of strings, you cannot directly use the Contains(string) method. Instead, you need to convert the string[] array into a collection that supports the Contains() method. Here are two approaches:

1. Using a List:

Convert the string[] array into a List and then use the Contains() method on the list:

var uids = new List<string>(stringArray);
var selected = table.Where(t => uids.Contains(t.uid.ToString()));

2. Using a List (if uid is also an int):

If uid is also an integer, you can convert the string[] array into a List and then use the Contains() method on the list:

var uids = stringArray.Select(int.Parse).ToList();
var selected = table.Where(t => uids.Contains(t.uid));

Extension Method (Optional):

You can also create an extension method for the string[] type to provide a Contains() method that takes a string argument:

public static bool Contains(this string[] arr, string value)
{
    return arr.Any(s => s == value);
}

With this extension method, you can directly use the Contains() method on the string[] array:

var selected = table.Where(t => stringArray.Contains(t.uid.ToString()));

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