如何根据其中一个关键值将此连接查询的结果转换为dict？

Question

Sorry i'm a bit new to all this.

I'm using psycopg2, python, and postgres.

I have two tables - Users and Events. I've set up a many-to-many relationship because an event can have many users and users can join many events. There's an intermediate table called UsersEvents matching User id to Event id. I want to get the list of events and users in a dict similar to this:

[
    {
        event_id: 1,
        event_name : 'event-name',
        joined : [
            {'username' : 'name'},
            {'username' : 'name'},
            {'username' : 'name'}
        ]
    },
    {
        event_id: 2,
        event_name : 'event2-name',
        joined : [
            {'username' : 'name2'},
            {'username' : 'name2'}
        ]
    }
]

I'm running a query like this with psycopg2 to get the list of events and users associated with them:

SELECT events.id, event_name, users.username
FROM events
JOIN usersevents on events_id = events.id
JOIN users on usersevents.users_id = users.id;

which returns me back something like this:

[
    (1, 'event-name', 'name'),
    (1, 'event-name', 'name'), 
    (1, 'event-name', 'name'), 
    (2, 'event2-name', 'name2'),
    (2, 'event2-name', 'name2')
]

So it's great that it pulls back the information I need but now I have to try and figure out how to merge it into the format above. Is there a better query for what I'm trying to do, or should I just loop through all the results and try merging results with the same event name?

Edit: I understand how to return the results as a dict as pointed out in the comments. I want to take the rows that have duplicate event names and nest the users joining that event into a single dict row for a single event object.

Answer 1

You want to build a data structure for each event by name. Create a dict that will map names to event data. For each row, either create or update the data for the event. Finally, the values from the dict is the list of event data.

for id, event, user in results:
    event = events.setdefault(id, {'event_id': id, 'event_name': name, 'joined': []})
    event['joined'].append({'username': user})

data = list(events.values())