【发布时间】：2018-07-20 15:33:25
【问题描述】：
这里有a sibling question in Software Engineering SE。
考虑Company、Product 和Person。
Company 和 Product 之间存在多对多关系，通过联结表 Company_Product，因为给定的公司可能生产不止一种产品（例如“汽车”和“自行车”） ，而且一个给定的产品，比如“汽车”，可以由多家公司生产。在联结表Company_Product 中有一个额外的字段“价格”，它是给定公司销售给定产品的价格。
Company_Product 和 Person 之间还有另一个多对多关系，通过联结表 Company_Product_Person。是的，它是一种多对多关系，涉及一个已经是联结表的实体。这是因为一个人可以拥有多个产品，例如 company1 的汽车和 company2 的自行车，而同一个 company_product 可以由多个人拥有，因为例如 person1 和 person2 都可能从公司 1.在联结表Company_Product_Person 中有一个额外的字段“想法”，其中包含该人在购买 company_product 时的想法。
我想使用sequelize 进行查询，以从数据库中获取Company 的所有实例，以及所有相关的Products 和各自的Company_Product，这反过来又包括所有相关的Persons 和各自的@ 987654338@.
获取两个联结表的元素也很重要，因为“价格”和“想法”字段很重要。
我不知道该怎么做。
为了调查这个问题，我尽量缩短了代码。 看起来很大，但大部分都是模型声明样板：（要运行它，首先要执行npm install sequelize sqlite3）
const Sequelize = require("sequelize");
const sequelize = new Sequelize({ dialect: "sqlite", storage: "db.sqlite" });
// ================= MODELS =================
const Company = sequelize.define("company", {
id: {
type: Sequelize.INTEGER,
allowNull: false,
autoIncrement: true,
primaryKey: true
},
name: Sequelize.STRING
});
const Product = sequelize.define("product", {
id: {
type: Sequelize.INTEGER,
allowNull: false,
autoIncrement: true,
primaryKey: true
},
name: Sequelize.STRING
});
const Person = sequelize.define("person", {
id: {
type: Sequelize.INTEGER,
allowNull: false,
autoIncrement: true,
primaryKey: true
},
name: Sequelize.STRING
});
const Company_Product = sequelize.define("company_product", {
id: {
type: Sequelize.INTEGER,
allowNull: false,
autoIncrement: true,
primaryKey: true
},
companyId: {
type: Sequelize.INTEGER,
allowNull: false,
references: {
model: "company",
key: "id"
},
onDelete: "CASCADE"
},
productId: {
type: Sequelize.INTEGER,
allowNull: false,
references: {
model: "product",
key: "id"
},
onDelete: "CASCADE"
},
price: Sequelize.INTEGER
});
const Company_Product_Person = sequelize.define("company_product_person", {
id: {
type: Sequelize.INTEGER,
allowNull: false,
autoIncrement: true,
primaryKey: true
},
companyProductId: {
type: Sequelize.INTEGER,
allowNull: false,
references: {
model: "company_product",
key: "id"
},
onDelete: "CASCADE"
},
personId: {
type: Sequelize.INTEGER,
allowNull: false,
references: {
model: "person",
key: "id"
},
onDelete: "CASCADE"
},
thoughts: Sequelize.STRING
});
// ================= RELATIONS =================
// Many to Many relationship between Company and Product
Company.belongsToMany(Product, { through: "company_product", foreignKey: "companyId", onDelete: "CASCADE" });
Product.belongsToMany(Company, { through: "company_product", foreignKey: "productId", onDelete: "CASCADE" });
// Many to Many relationship between Company_Product and Person
Company_Product.belongsToMany(Person, { through: "company_product_person", foreignKey: "companyProductId", onDelete: "CASCADE" });
Person.belongsToMany(Company_Product, { through: "company_product_person", foreignKey: "personId", onDelete: "CASCADE" });
// ================= TEST =================
var company, product, person, company_product, company_product_person;
sequelize.sync({ force: true })
.then(() => {
// Create one company, one product and one person for tests.
return Promise.all([
Company.create({ name: "Company test" }).then(created => { company = created }),
Product.create({ name: "Product test" }).then(created => { product = created }),
Person.create({ name: "Person test" }).then(created => { person = created }),
]);
})
.then(() => {
// company produces product
return company.addProduct(product);
})
.then(() => {
// Get the company_product for tests
return Company_Product.findAll().then(found => { company_product = found[0] });
})
.then(() => {
// person owns company_product
return company_product.addPerson(person);
})
.then(() => {
// I can get the list of Companys with their Products, but couldn't get the nested Persons...
return Company.findAll({
include: [{
model: Product
}]
}).then(companies => {
console.log(JSON.stringify(companies.map(company => company.toJSON()), null, 4));
});
})
.then(() => {
// And I can get the list of Company_Products with their Persons...
return Company_Product.findAll({
include: [{
model: Person
}]
}).then(companyproducts => {
console.log(JSON.stringify(companyproducts.map(companyproduct => companyproduct.toJSON()), null, 4));
});
})
.then(() => {
// I should be able to make both calls above in one, getting those nested things
// at once, but how??
return Company.findAll({
include: [{
model: Product
// ???
}]
}).then(companies => {
console.log(JSON.stringify(companies.map(company => company.toJSON()), null, 4));
});
});
我的目标是一次性获得一组Companys 以及所有深层嵌套的Persons 和Company_Product_Persons：
// My goal:
[
{
"id": 1,
"name": "Company test",
"createdAt": "...",
"updatedAt": "...",
"products": [
{
"id": 1,
"name": "Product test",
"createdAt": "...",
"updatedAt": "...",
"company_product": {
"id": 1,
"companyId": 1,
"productId": 1,
"price": null,
"createdAt": "...",
"updatedAt": "...",
"persons": [
{
"id": 1,
"name": "Person test",
"createdAt": "...",
"updatedAt": "...",
"company_product_person": {
"id": 1,
"companyProductId": 1,
"personId": 1,
"thoughts": null,
"createdAt": "...",
"updatedAt": "..."
}
}
]
}
}
]
}
];
我该怎么做？
注意：我可以分别进行这两个查询并编写一些代码来“加入”检索到的对象，但这在计算上会很昂贵且很难看。我正在寻找正确的方法来做到这一点。
【问题讨论】：
标签： javascript node.js many-to-many sequelize.js eager-loading