Sequelize join twice on two tables - node.js

Question

I have two table: Conversations and ConversationParticipants.
I need to get the list of conversations that both users 1 and 2 participate too.
In MySQL, the query would be this:
SELECT conversation_participants.conversation_id FROM conversation_participants
JOIN conversations t1
ON t1.conversation_id = conversation_participants.conversation_id
AND conversation_participants.user_id = 11
JOIN conversation_participants t2
ON t1.conversation_id = t2.conversation_id
AND t2.user_id = 2
However, in Sequelize I cannot understand how to set models relations so that I can make a single query. I tried this without success (please note that this is almost pseudo code, reported as such for clarity):
var Conversation = sequelize.define('conversations', {
conversationId: Sequelize.INTEGER.UNSIGNED,
});
var ConversationParticipant = sequelize.define('conversation_participants', {
participationId: Sequelize.INTEGER.UNSIGNED,
userId: Sequelize.INTEGER.UNSIGNED,
conversationId : Sequelize.INTEGER.UNSIGNED,
});
Conversation.hasMany(ConversationParticipant, { as : 'Participants'});
and then
ConversationParticipant.findAll({
where : { userId : 1 },
include : [{
model : Conversation,
as : 'conversation',
include : [{
model : ConversationParticipant,
as : 'Participants',
where : { userId : 2 }
}]
}]
I get the following error:
Error: conversation_participants is not associated with conversations!.
Any idea?

Answer 1

One way you could do it is find the conversations that have participants with user 1 or 2, and afterwards filter the conversations that have both of them:
const userIdsFilter = [1,2];
//find Conversations that have user 1 OR user 2 as participants,
Conversation.findAll({
include : [{
model : ConversationParticipant,
as : 'conversation_participants',
where : { userId : { $in: userIdsFilter }}
}]
}).then((conversations) =>
{
//filter the conversations that have the same length participants
//as the userIdsFilter length (that way it excludes the ones
//that have just one of the users as participants)
return conversations.filter((conversation) =>
conversation.conversation_participants.length === userIdsFilter.length);
}).then((conversations) =>
{
//do what you need with conversations..
})

Answer 2

You are missing the belongsTo association in the ConversationParticipant definition. Sequelize model needs explicit association since you are trying to access Conversation via the ConversationParticipant instance even though Conversation is associated ConversationParticipant is not.
Something like this in addition to hasMany association:
ConversationParticipant.belongsTo(Conversation, { as : 'conversation',
foreignKey: 'conversationId', targetKey: 'conversationId'});
And then remove the conversationId field definition from ConversationParticipant model since belongsTo also creates that for you.