Linq subselect filter - linq

Question

probably someone can help me with this (at least for me) complicated problem.
Lets say i have the following data (in DB)
Tab1 (id_t1): Item
(1)
(2)
(3)
Tab2 (id_t2, id_t1): Group
(4, 1)
(5, 1)
(6, 2)
(7, 3)
Tab3 (id_t3, id_t2, v): GroupField
(10, 4, 100)
(11, 4, 300)
(12, 5, 200)
(13, 6, 100)
(14, 6, 200)
(15, 7, 100)
(16, 7, 300)
Now i'd like to select all Items that include all of some specific GroupFields.
Eg. i have v = list(100,200)
and i like to get back 1,2 but not 3
1 because Group4 holds the Field10 with v=100 and Group5 holds Field12 with v=200
and 2 because Group6 holds Field13 with v=100 and Field14 with v=200
Is something like this possible in Linq? (i allready tried different ways (any/all) but without success so far.
I don't get the point how to overcome that "field can be in any Group and not all in one Group"...
I don't even know how to do this in SQL in one command without using temp-tables/cursors.
_rene

Answer 1

Try this:
var result =
groups.Join(fields, o => o.Id, i => i.GroupId,
(o, i) => new { Group = o, Field = i } )
.GroupBy(x => x.Group.ItemId)
.Where(x => values.All(y => x.Any(z => z.Field.Value == y)))
.Select(x => x.Key)
.Distinct();
The following classes are used:
class Group
{
public Group(int id, int itemId)
{
Id = id;
ItemId = itemId;
}
public int Id { get; set; }
public int ItemId { get; set; }
}
class GroupField
{
public GroupField(int id, int groupId, int value)
{
Id = id;
GroupId = groupId;
Value = value;
}
public int Id { get; set; }
public int GroupId { get; set; }
public int Value { get; set; }
}
and the following initialization:
var groups = new [] { new Group(4, 1), new Group(5, 1),
new Group(6, 2), new Group(7, 3) };
var fields = new [] { new GroupField(10, 4, 100),
new GroupField(11, 4, 300),
new GroupField(12, 5, 200),
new GroupField(13, 6, 100),
new GroupField(14, 6, 200),
new GroupField(15, 7, 100),
new GroupField(16, 7, 300)
};
var values = new [] { 100, 200 };