为什么在使用对象属性进行查询时从MongoDB中获取空数组？

Question

在尝试从MongoDB检索文档时，我遇到了一个看似微不足道的问题，但仍然存在。我将Mongoose用作ODM，但在提取符合特定条件的文档时遇到了麻烦。我看过类似的问题/问题，但似乎没有建议对我有用。

下面是涉及获取与特定位置名称匹配的聚会对象的示例的片段。

export default {
  Query: {
    //...
    meetupsByLocation: async (parent, { location }, { Meetup }, info) => {
      try {
        const meetups = await Meetup.find({ 
          "location.name": { "$eq" : location, "$exists" : true } 
        });

        // Tried this one too but to no avail
        //const meetups = await Meetup.find({ "location.name": location });

        return meetups.map(meetup => {
          meetup._id = meetup._id.toString();
          return meetup;
        });
      } catch (error) {
        throw new Error(error.message);
      }
    }
    //...
  },

  Mutations: {
    //...
  },
};

Meetup GraphQL架构

export default `

scalar DateTime

type MeetupLocation {
  name: String!
  longitude: Float!
  latitude: Float!
}

type MeetupDetails {
  name: String!
  hostedBy: String!
  description: String!
  imageUrl: String!
  eventStart: DateTime!
  eventEnd: DateTime!
}

type Meetup {
  id: ID!
  addedBy: String!
  type: [String!]!
  location: MeetupLocation!
  details: MeetupDetails!
  photos: [String]!
  attendees: [String]!
  comments: [String]!
}

# Queries

type Query {
  meetupsByLocation(location: String!): [Meetup]!
}

`

Meupup猫鼬模式

import mongoose from 'mongoose';

const Schema = mongoose.Schema;

const MeetupSchema = new Schema(
  {
    addedBy: { type: Schema.Types.ObjectId, ref: 'User' },
    type: { type: [String] },
    location: { 
      name: { type: String },
      longitude: { type: Number },
      latitude: { type: Number },
    },
    details: { 
      name: { type: String },
      hostedBy: { type: Schema.Types.ObjectId, ref: 'User' },
      description: { type: String },
      imageUrl: { type: String },
      eventStart: { type: Date },
      eventEnd: { type: Date },
    },
    photos: { type: [String] },
    attendees: [{ type: Schema.Types.ObjectId, ref: 'User' }],
    comments: [{ type: Schema.Types.ObjectId, ref: 'Comment' }],
  },
  {
    timestamps: true,
  }
);

export default mongoose.model('Meetup', MeetupSchema);

NB ：已编辑以包含架构。