Django Q&Q versus filter.filter - sql

Question

While hunting a bug, I found out that the following 2 statements do different things:
Query 1
Order.objects \
.filter(items__name__icontains="Foo") \
.filter(items__name__icontains="Bar") \
.distinct()
Query 2
Order.objects \
.filter(
Q(items__name__icontains="Foo") &
Q(items__name__icontains="Bar")
) \
.distinct()
The result is as follows:
Query 1 does include orders that have items which either contain "Foo" or "Bar". For example one item's name is "Foo" while another item's name is "Bar".
Query 2 however only includes orders that have at least one item that contains all keywords, for example an item with a name of "Foo Bar".
Looking at the queries, I can see that the filter() method adds another INNER JOIN to the query while the other doesn't.
I can see the reasoning behind this, but I really wonder if that's the intended behavior.

Answer 1

The difference is that the first query has two filter() calls, and the second query only has one.
The first query tries to find an object with a related item containing 'Foo' and a related item containing 'Bar'. The second query tries to find an item with a single related item that contains both 'Foo' and 'Bar'
The fact that one uses Q() objects is not significant - you could change the first query to:
Order.object.filter(
Q(items__name__icontains="Foo"
).filter(
Q(items__name__icontains="Bar")
)
However the Q() is required in your second Query 2m since it would be invalid Python to repeat the keyword argument in .filter(items__name__icontains="Foo", items__name__icontains="Bar")
See the docs on spanning multi-values relationships for more info.