Sequelize联表查询的问题

问题

2个表相关联，一定要在2个表中的定义associate吗， 如下user表，post表， 一个用户可以有多篇文章，一篇文章只能属于一个用户

app.model.User.hasMany(app.model.Post, { as: 'posts' });

app.model.Post.belongsTo(app.model.User, { as: 'user', foreignKey: 'user_id' });

user表

  const User = app.model.define('user', {
    id: {
      type: INTEGER,
      primaryKey: true,
      autoIncrement: true,
    },
    name: STRING(30),
    age: INTEGER,
    created_at: DATE,
    updated_at: DATE,
  });

  User.prototype.associate = function() {
    app.model.User.hasMany(app.model.Post, { as: 'posts' });
  };

post

  const Post = app.model.define('post', {
    id: {
      type: INTEGER,
      primaryKey: true,
      autoIncrement: true,
    },
    title: STRING(30),
    content: STRING(255),
    user_id: INTEGER,
    created_at: DATE,
    updated_at: DATE,
  });

  Post.associate = function() {
    app.model.Post.belongsTo(app.model.User, { as: 'user', foreignKey: 'user_id' });
  };