Get missing Ids from a list of ids - entity-framework-core

Question

I'm trying to retrieve a list of missing Ids in database from another list of Ids in Entity Framework Core.
Is there a way to get this call in one line?
public static async Task<IEnumerable<TKey>> GetMissingIds<T, TKey>(
this IQueryable<T> db, IEnumerable<TKey> ids)
where T : BaseEntity<TKey>
{
var existingIds = await db
.AsNoTracking()
.Where(entity => ids.Contains(entity.Id))
.Select(entity => entity.Id)
.ToListAsync();
return ids.Except(existingIds);
}

Answer 1

EF Core supports only Contains with local collections (with small exceptions), so there is no effective way to retrieve Ids which are not present in database via LINQ Query.
Anyway there is third-party extensions which can do that linq2db.EntityFrameworkCore (note that I'm one of the creators).
Using this extension you can join local collection to LINQ query:
public static Task<IEnumerable<TKey>> GetMissingIds<T, TKey>(
this IQueryable<T> query, IEnumerable<TKey> ids, CabcellationToken cancellationToken = default)
where T : BaseEntity<TKey>
{
// we need context to retrieve options and mapping information from EF Core
var context = LinqToDBForEFTools.GetCurrentContext(query) ?? throw new InvalidOperationException();
// create linq2db connection
using var db = context.CreateLinqToDbConnection();
var resultQuery =
from id in ids.AsQueryable(db) // transform Ids to queryable
join e in query on id equals e.Id into gj
from e in gj.DefaultIfEmpty()
where e == null
select id;
// there can be collision with EF Core async extensions, so use ToListAsyncLinqToDB
return resultQuery.ToListAsyncLinqToDB(cancellationToken);
}
This is the sample of generated query:
SELECT
[id].[item]
FROM
(VALUES
(10248), (10249), (10250), (10251), (10252), (10253), (10254),
(10255), (10256), (10257), (10023)
) [id]([item])
LEFT JOIN (
SELECT
[e].[OrderID] as [e]
FROM
[Orders] [e]
) [t1] ON [id].[item] = [t1].[e]
WHERE
[t1].[e] IS NULL