On 16/12/2016 8:52 AM, Matthew Pava wrote:
I have a Document model that has an M2M-symmetrical field on itself.
The idea is that we can “link” documents to other documents. It’s
very simple to find the linked documents of a particular document, but
is there an easy way to get all the linked documents of the linked
documents of the document in question? I will probably have to write
my own QuerySet or ModelManager function, but I was just curious if
Django had something built in.
For example:
A is linked to J, C, K.
èJ is linked to A
èC is linked to A
èK is linked to A
B is linked to J, M, P.
èJ is linked to B
èM is linked to B
èP is linked to B
C is linked to O.
èO is linked to C
D is linked to O, P, R.
èO is linked to D
èP is linked to D
èR is linked to D
So when I get the entire “chain” of documents linked to A, I would get
something like this:
J, C, K, B, O, D, P, R, M
I would put a method on the document model to return a queryset with
respect to itself. To do this I would nominate the "through" table and
have a model class which maps to it. That model will have two PKs to the
document model. The document model method(s) which return querysets
query the "through" table.
Also have a look at select_related
https://docs.djangoproject.com/en/1.10/ref/models/querysets/#select-related
Since J is linked to A and B, K is linked to A, and C is linked to A
and O and O is linked to D, and D is linked to O and P, R is linked to
D and P is linked to B which is linked to M (and J).
Hmmm…my contrived example exploded on me more than I intended…
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