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

LINQ Equivalent of SQL's "IN" Statement

In this article, we'll tackle the task of writing a LINQ query that emulates the behavior of the SQL "IN" statement. This query will retrieve items that match a specified list of tags.

Imagine the following database schema that supports item tagging:

Items

• ItemId
• Brand
• Name
• Price
• Condition
• Description
• Active

Tags

• TagId
• Name
• Active

TagMap

• TagMapId
• TagId
• ItemId
• Active

Problem Statement:
Write a LINQ query that returns items matching a specified list of tags. For instance, if the desired tags are 2, 3, 4, and 7, the query should retrieve items with those tags.

Solution:
We can achieve this using the following LINQ query:

var TagIds = new[] { 2, 3, 4, 7 };
var q = from map in Context.TagMaps
where TagIds.Contains(map.TagId)
select map.Items;

The query first initializes an integer array TagIds with the desired tag IDs. It then joins the TagMaps table with this array using the Contains method, which checks if the TagId column of TagMaps exists in the TagIds array.

This query generates a parameterized "IN" clause in the SQL statement, ensuring efficient execution. It essentially translates to the following SQL:

SELECT Items
FROM TagMaps
WHERE TagId IN (2, 3, 4, 7);

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