Is it possible to modify Django Q() objects after construction?

Question

Is it possible to modify Django Q() objects after construction? I create a Q() object like so:

q = Q(foo=1)

is it possible to later change q to be the same as if I had constructed:

q2 = Q(foo=1, bar=2)

? There's no mention of such an interface in the Django docs that I could find.

I was looking for something like:

Q.append_clause(bar=2)

Institute

what exactly do you mean by "same as constructed"? do you mean modify the q object on the fly ? – Pentecostal

@karthikr: Updated question to better describe what I was looking for. – Institute

Ok. the PerrinHarkins' answer is what you are looking for then. – Pentecostal

Answer 1

You can just make another Q() object and AND them together: q2 = q & Q(bar=2)

Norther

Are you sure that's semantically identical? It may well be, but I know there can be gotchas. For instance, calling .filter(Q(parent__foo=1)).filter(Q(parent__bar=1)) is different than .filter(Q(parent__foo=1, parent__bar=1)) and I didn't want to fall afoul of anything like that. – Institute

Yes, they are identical. What matters is if there are two .filter calls or just one. – Lindalindahl

Answer 2

You can add Q objects together, using their add method. For example:

>>> q = Q(sender=x)
>>> q.add(Q(receiver=y), Q.AND)

The second argument to add is the connector, which can also be Q.OR

EDIT: My answer is merely a different way of doing what Perrin Harkins suggested, but regarding your other concern, about different behavior of filter depending on the way you construct the query, you don't have to worry about that if you join Q objects. My example is equivalent to filter(sender=x, receiver=y), and not filter(sender=x).filter(receiver=y), because Q objects, as far as I could see in a quick test, do an immediate AND on the clauses and don't have the special behavior of filter for multi-valued relations.

In any case, nothing like looking at the SQL and making sure it really is doing the same in your specific queries.

Elwaine

Answer 3

The answers here are a little old and unsatisfactory imo. So here is my answer

This is how you deep copy:

def deep_copy(q: Q) -> Q:
    new_q = Q()
    # Go through the children of a query: if it's another
    # query it will run this function recursively
    for sub_q in q.children:
        # Make sure you copy the connector in 
        # case of complicated queries
        new_q.connector = q.connector
        if isinstance(sub_q, Q):
            # This will run recursively on sub queries
            sub_q = get_employee_q(sub_q)
        else:
            pass # Do your modification here
        new_q.children.append(sub_q)
    return new_q

In the else condition is where your stuff (name='nathan' for example) is defined. You can change or delete that if you'd like and the Query should work fine.

Oestradiol

This is AMAZING! (Note: while it doesn't exactly answer the spirit of the question posted here, it answers the literal question, and is exactly what I was looking for!) THANK YOU for your answer! – Retro

Oh yeah, I was going to edit the answer to replace get_employee_q with deep_copy in the recursive call, but stack gives me an error about too many pending edits... Perhaps @Oestradiol - you can make the correction? – Retro

Would also be nice to, instead of pass, change it to something like this: sub_q = (sub_q[0], "whatever you want") # Do your modification here – Retro