Allow overwriting localField and foreignField when populating virtuals

[lcw0622]

Project.virtual('userInfo', {  
  ref: 'User',  
  localField: 'username',  
  foreignField: 'username',  
  justOne: true  
})  
projectModel.find().populate('userInfo')  

It return without userInfo field, but if I change foreignField to _id, it will report an error like:
CastError: Cast to ObjectId failed for value "username" at path "_id" for model "User".
Mongoose: 4.12.3
MongoDB: 2.2.34
NodeJS: 8.11.2

[lineus]

@lcw0622 The following complete example shows that population works. Can you edit it to show the error you are seeing?

6963.js

#!/usr/bin/env node
'use strict';

const assert = require('assert');
const mongoose = require('mongoose');
mongoose.Promise = global.Promise;
mongoose.connect('mongodb://localhost:27017/test', { useMongoClient: true});
const conn = mongoose.connection;
const Schema = mongoose.Schema;

const userSchema = new Schema({
  name: String,
  username: String
});

const projectSchema = new Schema({
  name: String,
  username: String
});

projectSchema.virtual('userInfo', {
  ref: 'user',
  localField: 'username',
  foreignField: 'username',
  justOne: true
});

const User = mongoose.model('user', userSchema);
const Project = mongoose.model('project', projectSchema);

const user = new User({ name: 'Billy', username: 'quickdraw' });
const project = new Project({ name: 'Outlaw', username: user.username });

async function run() {
  assert.strictEqual(mongoose.version, '4.12.3');
  await conn.dropDatabase();
  await user.save();
  await project.save();
  let doc = await Project.findOne({}).populate('userInfo');
  assert.strictEqual(doc.userInfo.name, 'Billy');
  console.log('Assertions passed.');
  return conn.close();
}

run();

Output:

issues: ./6963.js
Assertions passed.
issues:

[lineus]

did you also change the creation of the project doc to reflect the new field erp instead of username?

Here is the same code as above but with the Project path erp instead of username.

6963.js

#!/usr/bin/env node
'use strict';

const assert = require('assert');
const mongoose = require('mongoose');
mongoose.Promise = global.Promise;
mongoose.connect('mongodb://localhost:27017/test', { useMongoClient: true});
const conn = mongoose.connection;
const Schema = mongoose.Schema;

const userSchema = new Schema({
  name: String,
  username: String
});

const projectSchema = new Schema({
  name: String,
  erp: String // changed
});

projectSchema.virtual('userInfo', {
  ref: 'user',
  localField: 'erp', // changed
  foreignField: 'username',
  justOne: true
});

const User = mongoose.model('user', userSchema);
const Project = mongoose.model('project', projectSchema);

const user = new User({ name: 'Billy', username: 'quickdraw' });
const project = new Project({ name: 'Outlaw', erp: user.username }); // changed

async function run() {
  assert.strictEqual(mongoose.version, '4.12.3');
  await conn.dropDatabase();
  await user.save();
  await project.save();
  let doc = await Project.findOne({}).populate('userInfo');
  assert.strictEqual(doc.userInfo.name, 'Billy');
  console.log('Assertions passed.');
  return conn.close();
}

run();

Output:

issues: ./6963.js
Assertions passed.
issues:

[lcw0622]

Thanks, In fact I use toObject to output result document, and then I found the model.toObject function seems doesn't handle the virtual populate field.

#!/usr/bin/env node
'use strict';

const assert = require('assert');
const mongoose = require('mongoose');
mongoose.Promise = global.Promise;
mongoose.connect('mongodb://localhost:27017/test', { useMongoClient: true});
const conn = mongoose.connection;
const Schema = mongoose.Schema;

const userSchema = new Schema({
  name: String,
  username: String
});

const projectSchema = new Schema({
  name: String,
  username: String
});

projectSchema.virtual('userInfo', {
  ref: 'user',
  localField: 'username',
  foreignField: 'username',
  justOne: true
});

const User = mongoose.model('user', userSchema);
const Project = mongoose.model('project', projectSchema);

const user = new User({ name: 'Billy', username: 'quickdraw' });
const project = new Project({ name: 'Outlaw', username: user.username });

async function run() {
  assert.strictEqual(mongoose.version, '4.12.3');
  await conn.dropDatabase();
  await user.save();
  await project.save();
  let doc = await Project.findOne({}).populate('userInfo');
  let plainObj = doc.toObject()
  assert.strictEqual(plainObj.userInfo.name, 'Billy');
  console.log('Assertions passed.');
  return conn.close();
}

run();

Output:

(node:76898) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'name' of undefined
    at run (/Users/liuchengwei/Work/work/talos-backend/mongo.js:41:40)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)
(node:76898) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:76898) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

[lineus]

@lcw0622 you need to set the toObject virtuals option on the project schema to true in order to get virtual fields in the output of toObject().

const projectSchema = new Schema({
  name: String,
  username: String
}, { toObject: { virtuals: true } });

or

const projectSchema = new Schema({
  name: String,
  username: String
});

projectSchema.set('toObject', { virtuals: true });

[lcw0622]

@lineus It take effect! Thanks a lot~ Maybe I need ready API docs more careful T_T

[lcw0622]

@lineus By the way, may I ask for why not add foreignFiled for Schema reference definition or in populate option? thanks

var personSchema = Schema({
  _id: Schema.Types.ObjectId,
  name: String,
  age: Number,
  stories: [{ type: String, ref: 'Story', foreignField: 'storyName' }]
});

or

Person.
  findOne({ name: 'Ian Fleming' }).
  populate({
path: 'stories',
foreignField: 'storyName'
}).

[lineus]

@vkarpov15 I'll let you answer the question. Why do only virtuals accept the local and foreign field options as opposed to being able to set them in the schema or the populate object.

[vkarpov15]

Re: setting foreignField in the schema and in populate(), that's an interesting idea, we'll consider that for a future release.

[lcw0622]

Thanks ,@lineus and @vkarpov15 ~
I think it will be very helpful for SQL users translate such sql:

SELECT
  FIELD_A, 
  (SELECT T_B.FIELD_B FROM T_B WHERE T_B.FIELD_A = T_A.FIELD_A) AS FIELD_B
FROM T_A
WHERE T_A='SOME OTHER CONDITIONS'

[vkarpov15]

@lcw0622 unlikely to happen anytime soon, but thanks for the suggestion