双多对多关系

Question

In loopback I have defined two models with a double many-to-many relationship as follows:

action.json:

    {
      "name": "Action",
      "base": "PersistedModel",
      "idInjection": true,
      "options": {
        "validateUpsert": true
      },
      "properties": {
        "text": {
          "type": "string",
          "required": true
        }
      },
      "validations": [],
      "relations": {
        "benchmark": {
          "type": "hasAndBelongsToMany",
          "model": "Course",
          "foreignKey": "benchmark"
        },
        "main": {
          "type": "hasAndBelongsToMany",
          "model": "Course",
          "foreignKey": "main"
        }
      },
      "acls": [],
      "methods": {}
    }

course.json:

    {
      "name": "Course",
      "base": "TrashModel",
      "idInjection": true,
      "options": {
        "validateUpsert": true
      },
      "properties": {
        "name": {
          "type": "string",
          "required": true
        }
      },
      "validations": [],
      "relations": {
        "benchmark": {
          "type": "hasAndBelongsToMany",
          "model": "Action",
          "foreignKey": "benchmark"
        },
        "main": {
          "type": "hasAndBelongsToMany",
          "model": "Action",
          "foreignKey": "main"
        }
      },
      "acls": [],
      "methods": {}
    }

Now when I try to create a relation between an action model and a course model with the following PUT request:

http://localhost:3000/api/courses/57331a4eeff440cb02c886ae/benchmark/rel/5731d60da2c6d238e3c3d9b3

Then when I request the course model with the related action models included with the following GET request:

http://localhost:3000/api/courses/57331a4eeff440cb02c886ae?filter=%7B%22include%22%3A%5B%22benchmark%22%2C%22main%22%5D%7D

I get:

    {
      "name": "Introduction Lessons",
      "id": "57331a4eeff440cb02c886ae",
      "benchmark": [{
        "text": "text here",
        "id": "5731d60da2c6d238e3c3d9b3"
      }],
      "main": [{
        "text": "text here",
        "id": "5731d60da2c6d238e3c3d9b3"
      }]
    }

So apparently the action is now attached through both the benchmark as the main relation. How did this happen? Do I setup my models wrong?

Answer 1

From what I understand, when you use hasAndBelongsToMany relashionship, loopback uses a through table which it manages automatically for you.

I believe by default it calls itself From_modelTo_model. In order to have two such relashion you need to tell loopback to manage it differently otherwise they use the same through table.

Try with through option such as

Action

"benchmark": {
  "type": "hasAndBelongsToMany",
  "model": "Course",
  "foreignKey": "benchmark",
  "through":"ActionCourseBenchmark"
},
"main": {
  "type": "hasAndBelongsToMany",
  "model": "Course",
  "foreignKey": "main",
  "through":"ActionCourseMain"
}

Course

"benchmark": {
  "type": "hasAndBelongsToMany",
  "model": "Action",
  "foreignKey": "benchmark",
  "through":"ActionCourseBenchmark"
},
"main": {
  "type": "hasAndBelongsToMany",
  "model": "Action",
  "foreignKey": "main",
  "through":"ActionCourseMain"
}

see this github issue for more details