How to query custom defined join table - postgresql

Question

I have three models user, tab, subscription. User can subscribe to many tabs and tab can have many subscribers.
user --* subscription *-- tab
Diagram from navicat
sequelize.define('subscription', {})
Tab.belongsToMany(User, { through: Subscription })
User.belongsToMany(Tab, { through: Subscription })
How do I get all subscribers for specific tab or all tabs which specific user subscribes to?
I could do that in two queries but it have to be possible in one.
I have tried every possible combination of where, include, through which I would rather not share here. Every time I try to get access to subscription from any side I get subscription (subscriptions) is not associated to user.
I am trying to get something like this to work.
await Tab.findAll({
where: { name: ctx.params.tabname },
include: [{
model: Subscription,
through: {
where: { userUsername: ctx.params.username }
}
}]
})

Answer 1

The issue with belongsToMany is that is creates link directly to the destination entity. So to get all users for a specific tab you would have to do
Tab.findAll({
include: [{
model: User
}]
});
That works when you don't really want to get any data from the subscription entity.
In a case you want to select any data from the subscription entity you need to slightly modify your relations.
Tab.hasMany(Subscription);
Subscription.belongsTo(Tab);
User.hasMany(Subscription);
Subscription.belongsTo(User);
This will create one to many relation from tab to subscription and add also binding backwards from subscription to tab. The same thing for user.
Then you can query for all subscriptions (with user info) of a specific tab or for all subscriptions (with tab info) for a specific user like following:
Tab.findAll({
include: [{
model: Subscription,
include: [{
model: User
}]
}]
});
User.findAll({
include: [{
model: Subscription,
include: [{
model: Tab
}]
}]
});
I hope that helps!