Using Ecto's has_many or many_to_many to join tables on multiple columns

Questions / Help
1

I have a data model that looks like this:

%Game{
  id,
  team_id,
  date,
  ...
}

%WellnessEvaluation{
  id,
  athlete_id,
  team_id,
  date,
  ...
}

Is it possible to use Ecto’s has_many (or many_to_many) relationship between Game and WellnessEvaluation joining on date and team_id columns? The result would be a game on 2019-05-29 with a team_id of 1 would be able to get a list of Wellness Evaluations that have the corresponding date and team_id.

The convenience of being able to reference the Wellness Evaluations through a Game is appealing to me. As far as I understand these Ecto functions provide only the the ability to join on one column or through a join table which I don’t think would be necessary in this case.

1 Like
2

I’d suggest you look at:

  • Ecto’s many_to_many docs (you will need an intermediary table).
  • Ecto’s has_many docs – make sure to read the section on :through relationships.