RoR API如何将post用于关联

我正在使用RoR 6创建一个API项目。我有以下模型:

class Province < ApplicationRecord
  validates :province, presence: true, length: {minimum:5}, uniqueness: true
  has_many :cities, dependent: :destroy
end

class City < ApplicationRecord
  validates :city, presence: true, length: {minimum: 5}, uniqueness: true
  belongs_to :province
end

迁移:

class CreateProvinces < ActiveRecord::Migration[6.1]
  def change
    create_table :provinces do |t|
      t.string :province

      t.timestamps
    end
  end
end

class CreateCities < ActiveRecord::Migration[6.1]
  def change
    create_table :cities do |t|
      t.string :city
      t.references :province, null: false, foreign_key: true

      t.timestamps
    end
  end
end

def create
    @city = City.new(city_params)

    if @city.save
      render json: @city, status: :created, location: @city
    else
      render json: @city.errors, status: :unprocessable_entity
    end
  end

private
    def city_params
      params.require(:city).permit(:city, :province_id)
    end

Rails.application.routes.draw do
  resources :provinces, defaults: { format: :json } do
    resources :cities, defaults: { format: :json }
  end
end

curl --location --request POST 'http://127.0.0.1:3000/provinces/1/cities' \
--header 'Content-Type: application/json' \
--data-raw '{
    "city": "New City",
    "province": 1
}'

{“省”:[“必须存在”]}

p=Province.find(1)
c=City.new({city: 'New City', province: p})
c.save