ruby on rails - How to scope only the tags a user has used -

i writing rails 4.2 app models user, notecard, tag , tagging (for m-2-m relationship). tag can have multiple notecards , notecard can have multiple tags. card belongs user , tag doesn't belong user. how can scope tags user has used? want have index of tags , index of tags user has used.

thanks!

here schema, don't have idea on how implement clause index tags user has used. give idea, i'm looking this

def index_of_used_tags   #take tags, return have cards user end  class user < activerecord::base   has_many :comments   has_many :folders   has_many :cards end class tag < activerecord::base   has_many :taggings   has_many :cards, through: :taggings    validates_presence_of :name   validates_uniqueness_of :name end class folder < activerecord::base   belongs_to :user    validates_presence_of :name   validates_uniqueness_of :name, scope: :user_id end class card < activerecord::base   belongs_to :user   belongs_to :folder    has_many :taggings   has_many :tags, through: :taggins end 

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activerecord::schema.define(version: 20150604113358)   enable_extension "plpgsql"   create_table "cards", force: :cascade |t|     t.string   "object"     t.text     "content"     t.string   "source"     t.integer  "user_id"     t.integer  "folder_id"     t.datetime "created_at", null: false     t.datetime "updated_at", null: false   end   add_index "cards", ["folder_id"], name: "index_cards_on_folder_id", using: :btree   add_index "cards", ["user_id"], name: "index_cards_on_user_id", using: :btree   create_table "comments", force: :cascade |t|     t.text     "content"     t.string   "commentable_type"     t.integer  "commentable_id"     t.integer  "user_id"     t.datetime "created_at",       null: false     t.datetime "updated_at",       null: false   end   add_index "comments", ["user_id"], name: "index_comments_on_user_id", using: :btree   create_table "folders", force: :cascade |t|     t.string   "name"     t.integer  "user_id"     t.datetime "created_at", null: false     t.datetime "updated_at", null: false   end   add_index "folders", ["user_id"], name: "index_folders_on_user_id", using: :btree   create_table "taggings", force: :cascade |t|     t.integer  "card_id"     t.integer  "tag_id"     t.datetime "created_at", null: false     t.datetime "updated_at", null: false   end  add_index "taggings", ["card_id"], name: "index_taggings_on_card_id", using: :btree  add_index "taggings", ["tag_id"], name: "index_taggings_on_tag_id", using: :btree  create_table "tags", force: :cascade |t|    t.string   "name"    t.datetime "created_at", null: false    t.datetime "updated_at", null: false  end create_table "users", force: :cascade |t|   t.string   "fname"   t.string   "lname"   t.boolean  "admin",                  default: false   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.inet     "current_sign_in_ip"   t.inet     "last_sign_in_ip"   t.datetime "created_at",                             null: false   t.datetime "updated_at",                             null: false end add_index "users", ["email"], name: "index_users_on_email", unique: true, using: :btree add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree add_foreign_key "cards", "folders" add_foreign_key "cards", "users" add_foreign_key "comments", "users" add_foreign_key "folders", "users" add_foreign_key "taggings", "cards" add_foreign_key "taggings", "tags" end 

you can set has_many through relationship between user , tag

class user < activerecord::base   has_many :comments   has_many :folders   has_many :cards   has_many :tags, through: :cards end 

then user.tags give tags user has used.