多对多

在如今的社会，我们非常喜欢给人打上标签，比如 颜值逆天、暖烘烘、高富帅等等。高富帅并不是某一个人的专利，一个人可以被别人打上多个标签，一个标签也可以打在多个人上面。这就是多对多关系。

声明多对多关系需要用到belongsToMany方法。

  1. User.beblongsToMany(Tag, {through: 'user_tag'});
  2. Tag.belongsToMany(User, {through: 'user_tag'});

在多对多关系的表结构中，无论我们把关系 id 存在双方的任何一个表中，会出现上一节所提到的使用Book.hasOne(User)声明关系，有数据冗余的问题，所以在多对多关系下的表结构需要第三个表来保存它们之间的关系。

而这第三张表，就是上面的 user_tag 。里面有一个 userId 和一个 tagId 字段。

实例

1.新建 tag.ts 文件

  1. import Sequelize from 'sequelize';
  2. import {UserAttributes, UserInstance} from './user';
  4. export interface TagAttributes {
  5.   name: string;
  6. }
  8. export interface TagInstance extends Sequelize.Instance<TagAttributes>, TagAttributes {
  9.   id: number;
  11.   getUsers: Sequelize.BelongsToManyGetAssociationsMixin<UserInstance>,
  12.   addUsers: Sequelize.BelongsToManyAddAssociationsMixin<UserInstance, number, any>,
  13.   addUser: Sequelize.BelongsToManyAddAssociationMixin<UserInstance, number, any>,
  14.   setUser: Sequelize.BelongsToManySetAssociationsMixin<UserInstance, number, any>,
  15.   countUsers: Sequelize.BelongsToManyCountAssociationsMixin,
  16.   createUser: Sequelize.BelongsToManyCreateAssociationMixin<UserAttributes, UserInstance, any>,
  17.   hasUser: Sequelize.BelongsToManyHasAssociationMixin<UserInstance, number>,
  18.   hasUsers: Sequelize.BelongsToManyHasAssociationsMixin<UserInstance, number>,
  19.   removeUser: Sequelize.BelongsToManyRemoveAssociationMixin<UserInstance, number>,
  20.   removeUsers: Sequelize.BelongsToManyRemoveAssociationsMixin<UserInstance, number>,
  22. }
  24. export default function TagDefine(sequelize: Sequelize.Sequelize, dataTypes: Sequelize.DataTypes): Sequelize.Model<TagInstance, TagAttributes>  {
  25.     const S = dataTypes;
  26.     const Tag = sequelize.define<TagInstance, TagAttributes>('Tag', {
  27.         name: S.STRING
  28.     }, {
  29.         timestamps: false
  30.     });
  32.     (Tag as any).associate = function(this: typeof Tag, models){
  33.         this.belongsToMany(models.User, {through: 'user_tag'});
  34.     }
  36.     return Tag;
  37. }

2.在 user.ts 添加关系代码

  1.   getTags: Sequelize.BelongsToManyGetAssociationsMixin<TagInstance>,
  2.   addTags: Sequelize.BelongsToManyAddAssociationsMixin<TagInstance, number, any>,
  3.   addTag: Sequelize.BelongsToManyAddAssociationMixin<TagInstance, number, any>,
  4.   setTag: Sequelize.BelongsToManySetAssociationsMixin<TagInstance, number, any>,
  5.   countTags: Sequelize.BelongsToManyCountAssociationsMixin,
  6.   createTag: Sequelize.BelongsToManyCreateAssociationMixin<TagAttributes, TagInstance, any>,
  7.   hasTag: Sequelize.BelongsToManyHasAssociationMixin<TagInstance, number>,
  8.   hasTags: Sequelize.BelongsToManyHasAssociationsMixin<TagInstance, number>,
  9.   removeTag: Sequelize.BelongsToManyRemoveAssociationMixin<TagInstance, number>,
  10.   removeTags: Sequelize.BelongsToManyRemoveAssociationsMixin<TagInstance, number>,
  1.  (User as any).associate = function(this: typeof User,models){
  2.    // this.hasOne(models.Book);
  3.    this.hasMany(models.Book);
  4.    this.belongsToMany(models.Tag, { through: 'user_tag'});
  5. }

3.在 index.ts 里面添加验证代码

  1. import TagDefined, {TagAttributes, TagInstance} from './tag';
  3. const Tag = sequelize.import<TagInstance, TagAttributes>('./tag');
  5. let user = await User.create({email:'belovedyogurt@gmail.com',name: 'yugo'})
  6. await user.createTag({name: '萌新'}); // 为 yugo 添加一个标签
  8. let tag = (await Tag.findAll())[0]; // 拿到 tag 表中第一条数据
  10. const tagUser = (await tag.getUsers())[0]; // 拿到该标签关联的用户的第一个
  12. console.log(user.id == tagUser.id); // 俩边查出来的 user 是否相等

运行之后可以得到一个 true ，说明逻辑正确。而且在数据库中也创建了user_tag关联表，完成以上代码运行之后便可看到数据库中已存数据。