How to Implement SQL's 'IN' Statement Using LINQ?

Linq Implementation of SQL "IN" Statement

In the context of a tagging schema with tables Items, Tags, and TagMap, you seek a LINQ query that retrieves items corresponding to a specified list of tag IDs. In SQL, this is typically achieved using an IN statement.

To translate this into LINQ, you can utilize the Contains() method. Consider the following example:

var TagIds = new int[] {12, 32, 42};

var q = from map in Context.TagMaps
        where TagIds.Contains(map.TagId)
        select map.Items;

In this query:

• Context.TagMaps represents the TagMap table.
• The where clause checks if the TagId property of each TagMap instance is contained in the TagIds array of desired tag IDs.
• The select clause retrieves the Items property of each matching TagMap.

This query will generate an SQL IN statement similar to:

SELECT * FROM Items
WHERE TagId IN (12, 32, 42)

The resulting query will return the items that have at least one tag with an ID in the specified list.

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