Linq version of SQL "IN" statement - sql

Question

I have the following 3 tables as part of a simple "item tagging" schema:
==Items==
ItemId int
Brand varchar
Name varchar
Price money
Condition varchar
Description varchar
Active bit
==Tags==
TagId int
Name varchar
Active bit
==TagMap==
TagMapId int
TagId int (fk)
ItemId int (fk)
Active bit
I want to write a LINQ query to bring back Items that match a list of tags (e.g. TagId = 2,3,4,7). In my application context, examples of items would be "Computer Monitor", "Dress Shirt", "Guitar", etc. and examples of tags would be "electronics", "clothing", etc. I would normally accomplish this with a SQL IN Statement.

Answer 1

Something like
var TagIds = new int[] {12, 32, 42};
var q = from map in Context.TagMaps
where TagIds.Contains(map.TagId)
select map.Items;
should do what you need. This will generate an In ( 12, 32, 42 ) clause (or more specifically a parameterized IN clause if I'm not mistaken).

Answer 2

given array of items:
var list = new int[] {2,3,4}
use:
where list.Contains(tm.TagId)

Answer 3

List<int> tagIds = new List<int>() {2, 3, 4, 7};
int tagIdCount = tagIds.Count;
//
// Items that have any of the tags
// (any item may have any of the tags, not necessarily all of them
//
var ItemsAnyTags = db.Items
.Where(item => item.TagMaps
.Any(tm => tagIds.Contains(tm.TagId))
);
//
// Items that have ALL of the tags
// (any item may have extra tags that are not mentioned).
//
var ItemIdsForAllTags = db.TagMap
.Where(tm => tagIds.Contains(tm.TagId))
.GroupBy(tm => tm.ItemId)
.Where(g => g.Count() == tagIdCount)
.Select(g => g.Key);
//
var ItemsWithAllTags = db.Items
.Where(item => ItemsIdsForAllTags.Contains(item.ItemId));
//runs just one query against the database
List<Item> result = ItemsWithAllTags.ToList();

Answer 4

You can simply use,
var TagIds = {12, 32, 42}
var prod =entities.TagMaps.Where(tagmaps=> TagIds .Contains(tagmaps.TagId));

Answer 5

string[] names = {"John", "Cassandra", "Sarah"};
var results = (from n in db.Names
where names.Contains(n.Name)
select n).ToList();

Answer 6

You may create an extension method "IN()"
public static class Extension
{
public static bool IN(this object anyObject, params object[] list)
{ return list.Contains(anyObject); }
}
to be used like this
var q = from map in Context.TagMaps
where map.TagId.IN(2, 3, 4, 7)
select map.Items;
Or just use the inline array.Contains() notation:
var q = from map in Context.TagMaps
where new[]{2, 3, 4, 7}.Contains(map.TagId)
select map.Items;