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Question

用户可以上传曲目并创建播放列表。我有一个播放列表模型，我有一个playlist_track模型，适用于可以保存到播放列表的用户。我可以创建一个新的播放列表，但是如何在视图中将曲目添加到播放列表？

ActiveRecord::Schema.define(version: 2018_12_06_050857) do

  # These are extensions that must be enabled in order to support this database
  enable_extension "plpgsql"

  create_table "active_storage_attachments", force: :cascade do |t|
    t.string "name", null: false
    t.string "record_type", null: false
    t.bigint "record_id", null: false
    t.bigint "blob_id", null: false
    t.datetime "created_at", null: false
    t.index ["blob_id"], name: "index_active_storage_attachments_on_blob_id"
    t.index ["record_type", "record_id", "name", "blob_id"], name: "index_active_storage_attachments_uniqueness", unique: true
  end

  create_table "active_storage_blobs", force: :cascade do |t|
    t.string "key", null: false
    t.string "filename", null: false
    t.string "content_type"
    t.text "metadata"
    t.bigint "byte_size", null: false
    t.string "checksum", null: false
    t.datetime "created_at", null: false
    t.index ["key"], name: "index_active_storage_blobs_on_key", unique: true
  end

  create_table "playlist_tracks", force: :cascade do |t|
    t.integer "playlist_id"
    t.integer "track_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "playlists", force: :cascade do |t|
    t.string "title"
    t.integer "user_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "plays", force: :cascade do |t|
    t.integer "user_id"
    t.integer "track_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "tracks", force: :cascade do |t|
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "genre"
    t.integer "user_id"
    t.string "name"
    t.date "release_date"
  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.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "username"
    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

  add_foreign_key "active_storage_attachments", "active_storage_blobs", column: "blob_id"
end

这是我的赛道模型

class Track < ApplicationRecord
    has_many_attached :mp3

    belongs_to :user, optional: true
    has_many :playlist_tracks
    has_many :playlists, through: :playlist_tracks
    has_many :plays
end

这是我的playist_track模型

class PlaylistTrack < ApplicationRecord
    belongs_to :playlist
  belongs_to :track
end