我正在尝试加载belongs-to-many
关联,我正在加载三个嵌套关联。这是模型,导致三个数据库表programs
,programDates
和peopleProgramDates
program.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;
};
在我的控制器中,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()
是一个只返回相同对象数组的函数,所以在这里不应该相关。 addBusCount
和addVolunteerCount
应该同样不相关。
我认为问题可能是人们的程序日期不是真正的续集模型,而是belongsToMany through:
上的ProgramDate
关联的结果。
This post似乎建议我可以使用association:
属性来加载来自through
关联的数据,但查询会挂起应用程序。
如果我从查询中删除连接表,那么数据加载正常:
program.findAll( { include: [programDate] } )
奖励点:最终我真正需要的只是用peopleProgramDates
物品返回的programDate
计数。也许我可以简单地在programDates
模型上定义这个,但是我们也许可以在一个单独的问题中解决这个问题。然而,如果有令人信服的理由使用这种方法,例如性能,那么也许我们应该这样做。
解决方案是通过关联为belongsToMany
添加一个别名:
// program_date.js
ProgramDate.belongsToMany(person, {through: 'peopleProgramDates', as: 'peopleProgDates'});
然后引用include
属性中的别名:
program.findAll( { include: [{ model: programDate, include: [{association: 'peopleProgDates'}] }]} )