Many to Many fields and through table

[Mark Phillips]

Is there any downside to creating a through table in a many to many relationship when there isn't any "extra" related data, but there might be in the future? 

I have read that migrating from a simple m2m relationship to a m2m with a through table takes some jumping through hurdles, so I am considering creating the through table now in case "the powers that be" (ie end users!) decide we need some extra data for the relationship in the future.

Thanks!

Mark

[Simon Charette]

Hello Mark,

The only downside I can think of is that you won't be able to create
relationships from the m2m managers, you'll have to create the
relationship directly instead.

This isn't such a big issue if you plan on adding fields later to
the intermediary model later on anyway.

You can read more about the subject in the documentation[0]

Best,
Simon

[0] https://docs.djangoproject.com/en/2.0/topics/db/models/#intermediary-manytomany

[James Schneider]

I don't believe there is any downside other than the extra few lines required for the intermediary model definition. Functionally it is the same AFAIK.

-James

[johnasm...@gmail.com]

Hi Mark,

Thank you for your question, I might actually do the same. I just had issues on a model with 2 M2M relationships (one using an intermediary table, one without). 

I would just caveat what James Schneider said, there are some differences. My simply M2M relationship threw me Field Required Errors while the one using a intermediary table didn't, implicitly making the field required=False.

It seems like the default M2M is required as expected[1], but it's tricky to have the M2M through relationship not throw the same error.  

Best,
John

[1] https://code.djangoproject.com/ticket/7073

Note: I noticed this through DRF, haven't tested on a small reproducible case in pure Django.