javascript - 表达和 Sequelize : eager loading belongs to many associations hangs application

Question

我正在尝试急切加载 belongs-to-many 关联，我正在加载三个嵌套关联。这是模型，它们产生三个数据库表 programs 、 programDates 和 peopleProgramDatesprogram.js :

module.exports = function(sequelize, DataTypes) {
  const Program = sequelize.define('program', {
    name: DataTypes.STRING
  });

  Program.associate = ({programDate}) => {
    Program.hasMany(programDate);
  };

  return Program;
};

program_date.js :

module.exports = function(sequelize, DataTypes) {
  const ProgramDate = sequelize.define('programDate', {
    date: DataTypes.DATEONLY,
    volunteerLimit: DataTypes.INTEGER
  }, {
    indexes: [
      {
        unique: true,
        fields: ['programId', 'date']
      }
    ]
  });

  ProgramDate.associate = ({program, person}) => {
    ProgramDate.belongsTo(program);
    ProgramDate.belongsToMany(person, {through: 'peopleProgramDates'});
  };

  return ProgramDate;
};

在我的 Controller 中，我想返回一个包含所有程序、programDates 和 peopleProgramDates 的对象:

const {bus, family, person, volunteerType, program, programDate} = require('../models');

exports.get = (request, response) => {
  return Promise.all([
    bus.findAll({ include: [{model: family, include: [person]}] })
        .then(buses => buses.map(addBusCount)),
    volunteerType.findAll({include: [person]})
        .then(volunteerTypes => volunteerTypes.map(addVolunteerCount)),

    // this query hangs the application
    program.findAll( { include: [{ model: programDate, include: [{association: 'peopleProgramDates'}] }]} )
        .then(programs => programs.map(processPrograms))

  ])
      .then(([buses, volunteerTypes, programs]) =>
        response.render('pages/register', {
          buses,
          volunteerTypes,
          programs
        })
      );
};

目前，processPrograms() 是一个简单地返回相同对象数组的函数，因此不应与此处相关。 addBusCount 和 addVolunteerCount 同样不相关。

我认为问题可能是 peopleProgram 日期不是真正的 Sequelize 模型，而是 belongsToMany through: 上的 ProgramDate 关联的结果。

This post 似乎建议我可以使用 association: 属性来从 through 关联加载数据，但是查询会挂起应用程序。

如果我从查询中删除连接表，则数据加载正常:

program.findAll( { include: [programDate] } )

加分项:最终我真正需要的只是 peopleProgramDates 对象返回的 programDate 计数。也许我可以简单地在 programDates 模型上定义这样的东西，但是也许我们可以在一个单独的问题中解决这个问题。尽管如此，如果有一个令人信服的理由使用这种方法，例如性能，那么也许我们终究应该采用这种方式。

Answer 1

解决办法是通过关联给belongsToMany添加一个别名:

// program_date.js
ProgramDate.belongsToMany(person, {through: 'peopleProgramDates', as: 'peopleProgDates'});

然后在 include 属性中引用别名:

program.findAll( { include: [{ model: programDate, include: [{association: 'peopleProgDates'}] }]} )