如何使用均衡器加入同一张表？答案

【问题标题】：How can I join same table using sequalizer?如何使用均衡器加入同一张表？
【发布时间】：2020-06-19 04:43:02
【问题描述】：

我第一次使用均衡器并陷入困境

我有一个表格类别如下

我需要类似的详细信息

[{
    "id" : 7,
    "name": "Mobile Cover",
    parent: {
        "id": 1
        "name": "Mobile",
    }
},
{
    "id" : 9,
    "name": "Mobile Glass",
    parent: {
        "id": 1
        "name": "Mobile",
    }
},
{
    "id" : 8,
    "name": "Knife",
    parent: {
        "id": 4
        "name": "Kitchenware",
    }
}]

我尝试使用 include 但它不起作用

const result =  await category.findAll({
            where: {
                parentId: {
                    [Op.ne]: null
                }
            },
            include: {
                model: category,
                where: {
                    'id': 'category.parentId'
                }
            },
            order: [
                ["createdAt", "DESC"],
            ],
        });

返回错误

SequelizeDatabaseError: 指定的表名“类别”多于一次

有什么办法吗？

【问题讨论】：

你需要使用self join。
你必须为同一个Model创建一个hasMany关联，然后使用别名和as选项，然后你可以调用include的东西。

标签： node.js postgresql sequelize.js sequelize-typescript

【解决方案1】：

你需要定义一个关联如下 -

Category.belongsTo(Category, {
  foreignKey: "parentID",
  targetKey: "id"
});

【讨论】：

【解决方案2】：

在使用 include 之前，您需要根据它们的关系定义关联。 Sequelize 拥有所有传统类型的关系，例如 hasMany、BelogTo 等。

进一步查看链接：https://sequelize.org/master/manual/associations.html

【讨论】：

【解决方案3】：

续集版本："sequelize": "^5.21.3"。这是一个工作示例：

index.ts:

import { sequelize } from '../../db';
import Sequelize, { Model, DataTypes, Op } from 'sequelize';

class Category extends Model {}
Category.init(
  {
    id: {
      primaryKey: true,
      autoIncrement: true,
      allowNull: false,
      type: DataTypes.INTEGER,
    },
    name: DataTypes.STRING,
  },
  { sequelize, modelName: 'categories' },
);

Category.belongsTo(Category, { foreignKey: 'parentId', as: 'parent', targetKey: 'id' });

(async function test() {
  try {
    await sequelize.sync({ force: true });

    // seed
    const parent1 = { id: 1, name: 'Mobile' };
    const parent2 = { id: 4, name: 'Kitchenware' };
    await Category.bulkCreate([parent1, parent2]);
    await Category.bulkCreate([
      { id: 7, name: 'Mobile Cover', parentId: parent1.id },
      { id: 8, name: 'Knife', parentId: parent2.id },
      { id: 9, name: 'Mobile Glass', parentId: parent1.id },
    ]);

    // test
    const result = await Category.findAll({
      include: [
        {
          model: Category,
          required: true,
          as: 'parent',
          attributes: ['id', 'name'],
        },
      ],
      attributes: ['id', 'name'],
      raw: true,
    });
    console.log('result: ', result);
  } catch (error) {
    console.log(error);
  } finally {
    await sequelize.close();
  }
})();

执行结果：

Executing (default): DROP TABLE IF EXISTS "categories" CASCADE;
Executing (default): DROP TABLE IF EXISTS "categories" CASCADE;
Executing (default): CREATE TABLE IF NOT EXISTS "categories" ("id"   SERIAL , "name" VARCHAR(255), "parentId" INTEGER REFERENCES "categories" ("id") ON DELETE SET NULL 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 = 'categories' GROUP BY i.relname, ix.indexrelid, ix.indisprimary, ix.indisunique, ix.indkey ORDER BY i.relname;
Executing (default): INSERT INTO "categories" ("id","name") VALUES (1,'Mobile'),(4,'Kitchenware') RETURNING *;
Executing (default): INSERT INTO "categories" ("id","name","parentId") VALUES (7,'Mobile Cover',1),(8,'Knife',4),(9,'Mobile Glass',1) RETURNING *;
Executing (default): SELECT "categories"."id", "categories"."name", "parent"."id" AS "parent.id", "parent"."name" AS "parent.name" FROM "categories" AS "categories" INNER JOIN "categories" AS "parent" ON "categories"."parentId" = "parent"."id";
result:  [ { id: 7,
    name: 'Mobile Cover',
    'parent.id': 1,
    'parent.name': 'Mobile' },
  { id: 8,
    name: 'Knife',
    'parent.id': 4,
    'parent.name': 'Kitchenware' },
  { id: 9,
    name: 'Mobile Glass',
    'parent.id': 1,
    'parent.name': 'Mobile' } ]

查看数据库中的数据记录：

node-sequelize-examples=# select * from "categories";
 id |     name     | parentId
----+--------------+----------
  1 | Mobile       |
  4 | Kitchenware  |
  7 | Mobile Cover |        1
  8 | Knife        |        4
  9 | Mobile Glass |        1
(5 rows)

【讨论】：