Rails join on user column - ruby-on-rails

Question

I'm trying to get all Activities related to users of the same school (a string on the user object), but the error I'm getting is this:
Can't join 'Activity' to association named 'users'; perhaps you
misspelled it?
activity_controller.rb
#school = current_user.school
#bathroom = Activity.includes(:users).where(name: 'Bathroom').where( :user => { :school => #school} )
and the schema:
create_table "activities", force: :cascade do |t|
t.string "name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "student_id"
t.string "status"
t.integer "user_id"
t.index ["student_id"], name: "index_activities_on_student_id"
t.index ["user_id"], name: "index_activities_on_user_id"
end
create_table "users", force: :cascade do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.integer "sign_in_count", default: 0, null: false
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.string "current_sign_in_ip"
t.string "last_sign_in_ip"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.string "name"
t.string "grade"
t.string "school"
t.integer "maxout"
t.index ["email"], name: "index_users_on_email", unique: true
t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
end

Answer 1

Not users but user because Activity belongs to User
#bathroom = Activity.includes(:user).where(name: 'Bathroom').where( :users => { :school => #school} )
But User has many activities so User.includes(:activities)
Of course, you have to provide associations:
class Activity
belongs_to :user
class User
has_many :activities