Add EntityFrameworkQueryableExtensions.ToLookupAsync

We already have ToDictionaryAsync, however when loading associations often what you want is a lookup which you would otherwise have to construct using two separate statements:

var childLookup = await context.ChildEntities
.Where(c => Enumerable.Contains(parentIds, c.ParentId))
.ToLookupAsync(c => c.ParentId);

[ajcvickers]

@jcracknell You are correct. I’ll bring it up again with the team.

[ajcvickers]

Discussed with the team and we still feel this is better done without the additional copy.