Associations(关联)

Associations(关联)

本章节描述sequelize中不同关联类型，这里有4种类型的关联可以使用。

1. BelongsTo
2. HasOne
3. HasMany
4. BelongsToMany

基本概念

model分为source 和 target model。下面是例子：

class User extends Model {}
User.init({
  name: Sequelize.STRING,
  email: Sequelize.STRING
}, {
  sequelize,
  modelName: 'user'
});

class Project extends Model {}
Project.init({
  name: Sequelize.STRING
}, {
  sequelize,
  modelName: 'project'
});

User.hasOne(Project);

其中调用方法model属于source model（User），作为参数的model的属于target model。

外键

当你在model之间创建association时，sequelize会自动创建外键指针。

class Task extends Model {}
Task.init({ title: Sequelize.STRING }, { sequelize, modelName: 'task' });
class User extends Model {}
User.init({ username: Sequelize.STRING }, { sequelize, modelName: 'user' });

User.hasMany(Task); // Will add userId to Task model
Task.belongsTo(User); // Will also add userId to Task model

等价于以下sql语句：

CREATE TABLE IF NOT EXISTS "users" (
  "id" SERIAL,
  "username" VARCHAR(255),
  "createdAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "updatedAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  PRIMARY KEY ("id")
);

CREATE TABLE IF NOT EXISTS "tasks" (
  "id" SERIAL,
  "title" VARCHAR(255),
  "createdAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "updatedAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "userId" INTEGER REFERENCES "users" ("id") ON DELETE
  SET
    NULL ON UPDATE CASCADE,
    PRIMARY KEY ("id")
);

根据tasks和users model 之间的关系将userId外键注入tasks表，让userid作为对users表的引用。如果被引用的User被删除，userId会被设置为null。可以通过重写onUpdate和onDelete属性进行修改。validation 选项有 RESTRICT, CASCADE, NO ACTION, SET DEFAULT, SET NULL

class Document extends Model {}
Document.init({
  author: Sequelize.STRING
}, { sequelize, modelName: 'document' });
class Version extends Model {}
Version.init({
  timestamp: Sequelize.DATE
}, { sequelize, modelName: 'version' });

Document.hasMany(Version); // This adds documentId attribute to version
Document.belongsTo(Version, {
  as: 'Current',
  foreignKey: 'currentVersionId'
}); // This adds currentVersionId attribute to document

Document.hasMany(Version);
Document.belongsTo(Version, {
  as: 'Current',
  foreignKey: 'currentVersionId',
  constraints: false
});

CREATE TABLE IF NOT EXISTS "documents" (
  "id" SERIAL,
  "author" VARCHAR(255),
  "createdAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "updatedAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "currentVersionId" INTEGER,
  PRIMARY KEY ("id")
);

CREATE TABLE IF NOT EXISTS "versions" (
  "id" SERIAL,
  "timestamp" TIMESTAMP WITH TIME ZONE,
  "createdAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "updatedAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "documentId" INTEGER REFERENCES "documents" ("id") ON DELETE
  SET
    NULL ON UPDATE CASCADE,
    PRIMARY KEY ("id")
);

强制外键索引无需约束

class Trainer extends Model {}
Trainer.init({
  firstName: Sequelize.STRING,
  lastName: Sequelize.STRING
}, { sequelize, modelName: 'trainer' });

// Series will have a trainerId = Trainer.id foreign reference key
// after we call Trainer.hasMany(series)
class Series extends Model {}
Series.init({
  title: Sequelize.STRING,
  subTitle: Sequelize.STRING,
  description: Sequelize.TEXT,
  // Set FK relationship (hasMany) with `Trainer`
  trainerId: {
    type: Sequelize.INTEGER,
    references: {
      model: Trainer,
      key: 'id'
    }
  }
}, { sequelize, modelName: 'series' });

// Video will have seriesId = Series.id foreign reference key
// after we call Series.hasOne(Video)
class Video extends Model {}
Video.init({
  title: Sequelize.STRING,
  sequence: Sequelize.INTEGER,
  description: Sequelize.TEXT,
  // set relationship (hasOne) with `Series`
  seriesId: {
    type: Sequelize.INTEGER,
    references: {
      model: Series, // Can be both a string representing the table name or a Sequelize model
      key: 'id'
    }
  }
}, { sequelize, modelName: 'video' });

Series.hasOne(Video);
Trainer.hasMany(Series);

一般而言建议使用这种方式。