mongoose - populate sub-schema sub-array

问题

I'm trying to populate a sub-schema field.

A Project contains multiple ProjectFilters. Each ProjectFilter references one FilterValue. A FilterValue is contained into one (and only one) Filter.

ProjectSchema

const ProjectSchema = new Schema({
  title: String,
  filters: [ProjectFilter.schema],
}, {
  timestamps: true,
  toJSON: {
    virtuals: true,
  },
});

ProjectFilterSchema

const ProjectFilterSchema = new Schema({
  filterValue: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'FilterValue',
  },
  isMain: {
    type: Boolean,
    default: false,
  },
}, {
  toJSON: {
    virtuals: true,
  },
});

FilterSchema

const FilterSchema = new Schema({
  label: String,
  values: [FilterValue.schema],
}, {
  timestamps: true,
  toJSON: {
    virtuals: true
  },
});

FilterValueSchema

const FilterValueSchema = new Schema({
  label: String,
  color: String,
}, {
  toJSON: {
    virtuals: true,
  },
});

This query doesn't work. filterValue is null:

let query = Project.findById(req.params.projectId, { _id: 0, filters: 1 });
query.populate('filters.filterValue');

I have tried to use a virtual populate:

ProjectFilterSchema.virtual('usedValue', {
  ref: 'Filter',
  localField: 'filterValue',
  foreignField: 'values._id',
  justOne : true,
});

But this returns the whole Filter document, not only the FilterValue needed.

回答1:

In order to populate a subdocuments, first you will need to explicitly define the document collection to which the ID references to. That way, mongoose will know which collection to query.

(In Mongoose 4 you can populate documents across multiple levels)

//ES6 syntax
import mongoose from 'mongoose';

const Schema = mongoose.Schema;
const ObjectId = Schema.Types.ObjectId;

const FilterSchema = new Schema({
   label: String,
   filtervalues: [FilterValueSchema],
}, { collection: 'filter' })

const FilterValueSchema = new Schema({
   label: String,
   color: String,
}, { collection: 'filtervalue' })

const ProjectFilterSchema = new Schema({
   filterValue: {
   type: ObjectId,
   ref: 'filtervalue',
}, { collection: 'projectfilter' })

mongoose.model('filters', ProjectFilterSchema);
mongoose.model('projectfilter', ProjectFilterSchema);
mongoose.model('filtervalue', FilterValueSchema);

Project.findById(req.params.projectId, { _id: 0 })
  .populate('filters.filter.filterValue').

来源：https://stackoverflow.com/questions/42762588/mongoose-populate-sub-schema-sub-array

标签

mongoose

populate