环回4:多对多关系

问题描述

我正在尝试实现一种过滤具有多对多关系的表中数据的方法.

I am trying to implement a way to filter data in tables which have ManytoMany relationship.

我有以下表格job，job_category和category.

I have following tables job, job_category and category.

到目前为止，我正在考虑使用job_id对job_category进行查询，然后使用该结果通过IN()添加条件，但是我也找不到任何实现此选项的方法.

So far I am thinking in do a query to job_category using job_id and then use that result to add a condition using IN() but I do not find any way to impĺement this option either.

问题:

1. 如何在Loopback 4中实现ManytoMany关系?

1. How to implement ManytoMany relation in Loopback 4?

如何使用IN过滤查询?

How to filter a query using IN?

PD 我可以使用$ inq作为问题编号2.

PDI can use $inq for question number 2.

filter.where = {
   ...filter.where,
   id: {inq: [2, 7]},
};

推荐答案

您可以使用hasManyThrough关系在Loopback 4中实现多对多关系. hasManyThrough关系是hasMany关系的扩展.

You can implement a many-to-many relationship in Loopback 4 using the hasManyThrough relationship. The hasManyThrough relationship is an extension to the hasMany relationship.

当前，此功能是一个等待接受的请求请求.

Currently, this feature is a pull request waiting to be accepted.

https://github.com/strongloop/loopback-next/pull/2359

但是，此请求请求的代码已打包，可以通过以下方式安装和使用.

However, the code for this pull request has been packaged and can be installed and used the following way.

npm install --save @loopback/repository@git+https://[e-mail]/codejamninja/loopback-next.git#npm/codejamninja/has-many-through-using-has-many@1.11.0-rc.1

models/patient.model.ts

import { Entity, model, property, hasMany } from '@loopback/repository';
import { Appointment, Patient } from '../models';

@model()
export class Physician extends Entity {
  @property({
    type: 'string',
    id: true
  })
  id?: string;

  @hasMany(() => Patient, { through: () => Appointment })
  patients: Patient[];
}

repositories/Patient.repository.ts

import {
  DefaultCrudRepository,
  HasManyThroughRepositoryFactory,
  repository
} from '@loopback/repository';
import { inject, Getter } from '@loopback/core';
import { MemoryDataSource } from '../datasources';
import { Patient, Physician } from '../models';
import { AppointmentRepository, PhysicianRepository } from '../repositories';

export class PatientRepository extends DefaultCrudRepository<
  Patient,
  typeof Patient.prototype.id
> {
  public readonly physicians: HasManyThroughRepositoryFactory<
    Physician,
    typeof Patient.prototype.id
  >;

  constructor(
    @inject('datasources.memory')
    dataSource: MemoryDataSource,
    @repository.getter('AppointmentRepository')
    getAppointmentRepository: Getter<AppointmentRepository>,
    @repository.getter('PhysicianRepository')
    getPhysicianRepository: Getter<PhysicianRepository>
  ) {
    super(Patient, dataSource);
    this.physicians = this.createHasManyThroughRepositoryFactoryFor(
      'physicians',
      getPhysicianRepository,
      getAppointmentRepository // notice the through repository getter
    );
  }
}

下面的链接中有一个基本示例.

There is a basic example of this at the following link.

https://github.com/codejamninja/medical-practice-api

请注意，此API可能会在接受拉取请求之前更改.

Please note that this api may change before the pull request is accepted.

您可以在以下链接中了解有关这种关系的更多信息.

You can read more about how this relationship works at the following links.

https://loopback.io/doc/en/lb3/HasManyThrough -relations.html https://guides.rubyonrails.org/association_basics.html#有很多通过关联

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