javascript - [NodeJs][Sequelize] ReferenceError : Cannot access 'ModelName' before initialization

Question

目前，我使用 Node Js 13 和 ORM Sequelize v5 以及 ES6 中的所有这些(通过 package.json 中的“type”:“module”)实现了一个 API。

在这个项目中，当我尝试使用关联时出现问题。

我有三个相关的模型:author.js、authorbook.js 和 book.js。

作者.js:

import Sequelize from 'sequelize';
import AuthorBook from './authorbook.js';
import dotenv from 'dotenv';

dotenv.config();

const sequelize = new Sequelize(
  process.env.DB_DATABASE, process.env.DB_USERNAME, process.env.DB_PASSWORD,{
    host: process.env.DB_HOST,
    dialect: 'mysql'
  }
);

export default class Author extends Sequelize.Model {}
Author.init({
  firstName: {
    firstName: false,
    type: Sequelize.STRING(100)
  },
  lastName: {
    allowNull: false,
    type: Sequelize.STRING(100)
  }
}, { sequelize });

Author.hasMany(AuthorBook, {
  onUpdate: 'CASCADE'
});

book.js :

import Sequelize from 'sequelize';
import AuthorBook from './authorbook.js';
import dotenv from 'dotenv';

dotenv.config();

const sequelize = new Sequelize(
  process.env.DB_DATABASE, process.env.DB_USERNAME, process.env.DB_PASSWORD,{
    host: process.env.DB_HOST,
    dialect: 'mysql'
  }
);

export default class Book extends Sequelize.Model {}
Book.init({
  title: {
    firstName: false,
    type: Sequelize.STRING(100)
  }
}, { sequelize });

Book.hasMany(AuthorBook, {
  onUpdate: 'CASCADE'
});

authorbook.js :

import Sequelize from 'sequelize';
import Author from './author.js';
import Book from './book.js';
import dotenv from 'dotenv';

dotenv.config();

const sequelize = new Sequelize(
  process.env.DB_DATABASE, process.env.DB_USERNAME, process.env.DB_PASSWORD,{
    host: process.env.DB_HOST,
    dialect: 'mysql'
  }
);

export default class AuthorBook extends Sequelize.Model {}
AuthorBook.init({
  authorId: {
    type: Number,
    allowNull: false
  },
  bookId: {
    type: Number,
    allowNull: false
  },
}, { sequelize });

AuthorBook.belongsTo(Author, { foreignKey: 'authorId'});
AuthorBook.belongsTo(Book, { foreignKey: 'bookId'});

这是我在运行 cmd node src/server.js 时遇到的错误:

(node:23142) ExperimentalWarning: The ESM module loader is experimental.
file:///Users/alexandre/Documents/project/server/src/db/models/.js:18
Author.hasMany(AuthorBook, {
               ^

ReferenceError: Cannot access 'AuthorBook' before initialization
    at file:///Users/alexandre/Documents/project/server/src/db/models/author.js:38:22
    at ModuleJob.run (internal/modules/esm/module_job.js:110:37)
    at async Loader.import (internal/modules/esm/loader.js:176:24)

有人可以帮助我吗？

Answer 1

该错误意味着您的模块之间存在循环引用。您应该将模型放在像 index.ts 这样的模块中。并在这里建立关联。请注意我的文件目录结构:

例如。
./models/book.ts :

import Sequelize from 'sequelize';
import { sequelize } from '../../../db';

export default class Book extends Sequelize.Model {}
Book.init(
  {
    title: {
      allowNull: false,
      type: Sequelize.STRING(100),
    },
  },
  { sequelize, modelName: 'books' },
);

./models/author.ts :

import Sequelize from 'sequelize';
import { sequelize } from '../../../db';

export default class Author extends Sequelize.Model {}
Author.init(
  {
    firstName: {
      allowNull: false,
      type: Sequelize.STRING(100),
    },
    lastName: {
      allowNull: false,
      type: Sequelize.STRING(100),
    },
  },
  { sequelize, modelName: 'authors' },
);

./models/authorbook.ts :

import Sequelize from 'sequelize';
import { sequelize } from '../../../db';

export default class AuthorBook extends Sequelize.Model {}
AuthorBook.init(
  {
    authorId: {
      type: Sequelize.INTEGER,
      allowNull: false,
    },
    bookId: {
      type: Sequelize.INTEGER,
      allowNull: false,
    },
  },
  { sequelize, modelName: 'authorbooks' },
);

./models/index.ts :

import Author from './author';
import Book from './book';
import AuthorBook from './authorbook';

Author.hasMany(AuthorBook, {
  onUpdate: 'CASCADE',
});
Book.hasMany(AuthorBook, {
  onUpdate: 'CASCADE',
});
AuthorBook.belongsTo(Author, { foreignKey: 'authorId' });
AuthorBook.belongsTo(Book, { foreignKey: 'bookId' });

export { Author, Book, AuthorBook };

现在，我们可以使用这些模型。
index.ts :

import { Author, AuthorBook, Book } from './models';
import { sequelize } from '../../db';
import faker from 'faker';

(async function test() {
  try {
    await sequelize.sync({ force: true });
    // seed
    const author = await Author.create({
      firstName: faker.name.firstName(),
      lastName: faker.name.lastName(),
    });
    const book = await Book.create({
      title: faker.lorem.words(3),
    });
    await AuthorBook.create({ authorId: author.id, bookId: book.id });
  } catch (error) {
    console.log(error);
  } finally {
    await sequelize.close();
  }
})();

执行结果:

Executing (default): DROP TABLE IF EXISTS "authorbooks" CASCADE;
Executing (default): DROP TABLE IF EXISTS "books" CASCADE;
Executing (default): DROP TABLE IF EXISTS "authors" CASCADE;
Executing (default): DROP TABLE IF EXISTS "authors" CASCADE;
Executing (default): CREATE TABLE IF NOT EXISTS "authors" ("id"   SERIAL , "firstName" VARCHAR(100) NOT NULL, "lastName" VARCHAR(100) NOT NULL, PRIMARY KEY ("id"));
Executing (default): SELECT i.relname AS name, ix.indisprimary AS primary, ix.indisunique AS unique, ix.indkey AS indkey, array_agg(a.attnum) as column_indexes, array_agg(a.attname) AS column_names, pg_get_indexdef(ix.indexrelid) AS definition FROM pg_class t, pg_class i, pg_index ix, pg_attribute a WHERE t.oid = ix.indrelid AND i.oid = ix.indexrelid AND a.attrelid = t.oid AND t.relkind = 'r' and t.relname = 'authors' GROUP BY i.relname, ix.indexrelid, ix.indisprimary, ix.indisunique, ix.indkey ORDER BY i.relname;
Executing (default): DROP TABLE IF EXISTS "books" CASCADE;
Executing (default): CREATE TABLE IF NOT EXISTS "books" ("id"   SERIAL , "title" VARCHAR(100) NOT NULL, PRIMARY KEY ("id"));
Executing (default): SELECT i.relname AS name, ix.indisprimary AS primary, ix.indisunique AS unique, ix.indkey AS indkey, array_agg(a.attnum) as column_indexes, array_agg(a.attname) AS column_names, pg_get_indexdef(ix.indexrelid) AS definition FROM pg_class t, pg_class i, pg_index ix, pg_attribute a WHERE t.oid = ix.indrelid AND i.oid = ix.indexrelid AND a.attrelid = t.oid AND t.relkind = 'r' and t.relname = 'books' GROUP BY i.relname, ix.indexrelid, ix.indisprimary, ix.indisunique, ix.indkey ORDER BY i.relname;
Executing (default): DROP TABLE IF EXISTS "authorbooks" CASCADE;
Executing (default): CREATE TABLE IF NOT EXISTS "authorbooks" ("id"   SERIAL , "authorId" INTEGER NOT NULL REFERENCES "authors" ("id") ON DELETE CASCADE ON UPDATE CASCADE, "bookId" INTEGER NOT NULL REFERENCES "books" ("id") ON DELETE CASCADE ON UPDATE CASCADE, PRIMARY KEY ("id"));
Executing (default): SELECT i.relname AS name, ix.indisprimary AS primary, ix.indisunique AS unique, ix.indkey AS indkey, array_agg(a.attnum) as column_indexes, array_agg(a.attname) AS column_names, pg_get_indexdef(ix.indexrelid) AS definition FROM pg_class t, pg_class i, pg_index ix, pg_attribute a WHERE t.oid = ix.indrelid AND i.oid = ix.indexrelid AND a.attrelid = t.oid AND t.relkind = 'r' and t.relname = 'authorbooks' GROUP BY i.relname, ix.indexrelid, ix.indisprimary, ix.indisunique, ix.indkey ORDER BY i.relname;
Executing (default): INSERT INTO "authors" ("id","firstName","lastName") VALUES (DEFAULT,$1,$2) RETURNING *;
Executing (default): INSERT INTO "books" ("id","title") VALUES (DEFAULT,$1) RETURNING *;
Executing (default): INSERT INTO "authorbooks" ("id","authorId","bookId") VALUES (DEFAULT,$1,$2) RETURNING *;

检查数据库:

node-sequelize-examples=# select * from "authors";
 id | firstName | lastName
----+-----------+----------
  1 | Laron     | Deckow
(1 row)

node-sequelize-examples=# select * from "books";
 id |          title
----+-------------------------
  1 | facilis molestias sequi
(1 row)

node-sequelize-examples=# select * from "authorbooks";
 id | authorId | bookId
----+----------+--------
  1 |        1 |      1
(1 row)

依赖版本: "sequelize": "^5.21.3" , postgres:9.6
源代码: https://github.com/mrdulin/node-sequelize-examples/tree/master/src/examples/stackoverflow/61163520