I have a project on which users may be registered to different challenges. And I would want to implement a "news" panel, where users are notified of events performed by other users, which have at least one challenge in common.
My DB schema has tables like follows :
table "user"
user_id
etc.
table "challenge"
challenge_id
etc.
table "user_challenge_association"
user_id
challenge_id
team_id
table "activity"
user_id
I would thus want to perform a request returning all activities of all users which have at least one entry in "user_challenge_association" where "challenge_id" is the same as another entry in "user_challenge_association" associated to the user for which I am doing the request.
Imagine "user" contains (user_1, user_2, user_3), imaging "challenge" contains (challenge_1, challenge_2), imagine that user_1 is only registered to challenge_1 user_2 is only registered to challenge_2, and user_3 is registered to both challenges, I would want :
that request for user_1 only returns activities of user_3
that request for user_2 only returns activities of user_3
that request for user_3 returns activities of user_1 and user_2
What would be the best way to perform such a query ?
Additional question : How could I integrate in the result a column indicating if, in all existing challenges, the resulting activity is linked to a user that was at least once in the same team as the user for which we perform the request ? (team information is in "user_challenge_association" table
