Community.js

module.exports = {

  attributes: {
    name: 'string',
    slug: 'string',
    users: {
      collection: 'user',
      via: 'communities',
      through: 'communityuser'
    }
  },

  autoCreatedAt: false,
  autoUpdatedAt: false

};

CommunityUser.js

module.exports = {

  tableName: 'users_community',
  tables: ['communities', 'users'],
  junctionTable: true,

  attributes: {
    name: 'string',
    email: 'string',
    users: {
      columnName: 'users_id',
      type: 'integer',
      foreignKey: true,
      references: 'user',
      on: 'id',
      via: 'communities',
      groupBy: 'user'
    },
    communities: {
      columnName: 'community_id',
      type: 'integer',
      foreignKey: true,
      references: 'community',
      on: 'id',
      via: 'users',
      groupBy: 'community'
    }
  },

  autoCreatedAt: false,
  autoUpdatedAt: false

};

query.sql

-- this is what happens when i load /community/9/users.
-- the problem is that 2 of the users are in many communities,
-- and that inner join causes one row for each community they're in.
-- so the result set only has 2 distinct users when there should be 30.
--
-- duplicates are being removed at some point in the code, but the
-- limit should be applied after that, not before.

SELECT
  "user"."name",
  "user"."email",
  "user"."id",
  "users_community"."community_id" AS "___community_id" 
FROM "users" AS "user"  
INNER JOIN "users_community" ON "users_community"."users_id" = "user"."id" 
WHERE "user"."id" IN (
  SELECT "users_community"."users_id" 
  FROM "users_community" 
  WHERE "users_community"."community_id" = '9' 
)  LIMIT 30 OFFSET 0

User.js

module.exports = {

  attributes: {
    name: 'string',
    email: 'string',
    communities: {
      collection: 'community',
      via: 'users',
      through: 'communityuser'
    }
  },

  tableName: 'users',
  autoCreatedAt: false,
  autoUpdatedAt: false

};

Were you able to solve this issue? Also, have you had luck actually posting to POST /community/:id/users? I'm finding that I have to set these routes up myself; have not had any luck getting Waterline to handle it natively.