在 Mongoose 中填充后查询

工作示例

下面给出一个在模型上使用静态方法的例子。一旦实现了该静态方法，调用就变成了：

  Item.lookup(
    {
      path: 'tags',
      query: { 'tags.tagName' : { '$in': [ 'funny', 'politics' ] } }
    },
    callback
  )

或者增强为更现代一点，甚至变成：

  let results = await Item.lookup({
    path: 'tags',
    query: { 'tagName' : { '$in': [ 'funny', 'politics' ] } }
  })

使其在结构上与 .populate() 非常相似，但它实际上是在服务器上进行连接。为了完整起见，这里的用法根据父子案例将返回的数据转换回 mongoose 文档实例。

对于大多数常见情况，它相当简单且易于适应或仅按原样使用。

注意这里使用 async 只是为了简洁地运行随附的示例。实际的实现没有这种依赖。

const async = require('async'),
      mongoose = require('mongoose'),
      Schema = mongoose.Schema;

mongoose.Promise = global.Promise;
mongoose.set('debug', true);
mongoose.connect('mongodb://localhost/looktest');

const itemTagSchema = new Schema({
  tagName: String
});

const itemSchema = new Schema({
  dateCreated: { type: Date, default: Date.now },
  title: String,
  description: String,
  tags: [{ type: Schema.Types.ObjectId, ref: 'ItemTag' }]
});

itemSchema.statics.lookup = function(opt,callback) {
  let rel =
    mongoose.model(this.schema.path(opt.path).caster.options.ref);

  let group = { "$group": { } };
  this.schema.eachPath(p =>
    group.$group[p] = (p === "_id") ? "$_id" :
      (p === opt.path) ? { "$push": `$${p}` } : { "$first": `$${p}` });

  let pipeline = [
    { "$lookup": {
      "from": rel.collection.name,
      "as": opt.path,
      "localField": opt.path,
      "foreignField": "_id"
    }},
    { "$unwind": `$${opt.path}` },
    { "$match": opt.query },
    group
  ];

  this.aggregate(pipeline,(err,result) => {
    if (err) callback(err);
    result = result.map(m => {
      m[opt.path] = m[opt.path].map(r => rel(r));
      return this(m);
    });
    callback(err,result);
  });
}

const Item = mongoose.model('Item', itemSchema);
const ItemTag = mongoose.model('ItemTag', itemTagSchema);

function log(body) {
  console.log(JSON.stringify(body, undefined, 2))
}
async.series(
  [
    // Clean data
    (callback) => async.each(mongoose.models,(model,callback) =>
      model.remove({},callback),callback),

    // Create tags and items
    (callback) =>
      async.waterfall(
        [
          (callback) =>
            ItemTag.create([{ "tagName": "movies" }, { "tagName": "funny" }],
              callback),

          (tags, callback) =>
            Item.create({ "title": "Something","description": "An item",
              "tags": tags },callback)
        ],
        callback
      ),

    // Query with our static
    (callback) =>
      Item.lookup(
        {
          path: 'tags',
          query: { 'tags.tagName' : { '$in': [ 'funny', 'politics' ] } }
        },
        callback
      )
  ],
  (err,results) => {
    if (err) throw err;
    let result = results.pop();
    log(result);
    mongoose.disconnect();
  }
)

或者更现代一点的 Node 8.x 及更高版本，带有 async/await 并且没有额外的依赖项：

const { Schema } = mongoose = require('mongoose');
const uri = 'mongodb://localhost/looktest';

mongoose.Promise = global.Promise;
mongoose.set('debug', true);

const itemTagSchema = new Schema({
  tagName: String
});

const itemSchema = new Schema({
  dateCreated: { type: Date, default: Date.now },
  title: String,
  description: String,
  tags: [{ type: Schema.Types.ObjectId, ref: 'ItemTag' }]
});

itemSchema.statics.lookup = function(opt) {
  let rel =
    mongoose.model(this.schema.path(opt.path).caster.options.ref);

  let group = { "$group": { } };
  this.schema.eachPath(p =>
    group.$group[p] = (p === "_id") ? "$_id" :
      (p === opt.path) ? { "$push": `$${p}` } : { "$first": `$${p}` });

  let pipeline = [
    { "$lookup": {
      "from": rel.collection.name,
      "as": opt.path,
      "localField": opt.path,
      "foreignField": "_id"
    }},
    { "$unwind": `$${opt.path}` },
    { "$match": opt.query },
    group
  ];

  return this.aggregate(pipeline).exec().then(r => r.map(m => 
    this({ ...m, [opt.path]: m[opt.path].map(r => rel(r)) })
  ));
}

const Item = mongoose.model('Item', itemSchema);
const ItemTag = mongoose.model('ItemTag', itemTagSchema);

const log = body => console.log(JSON.stringify(body, undefined, 2));

(async function() {
  try {

    const conn = await mongoose.connect(uri);

    // Clean data
    await Promise.all(Object.entries(conn.models).map(([k,m]) => m.remove()));

    // Create tags and items
    const tags = await ItemTag.create(
      ["movies", "funny"].map(tagName =>({ tagName }))
    );
    const item = await Item.create({ 
      "title": "Something",
      "description": "An item",
      tags 
    });

    // Query with our static
    const result = (await Item.lookup({
      path: 'tags',
      query: { 'tags.tagName' : { '$in': [ 'funny', 'politics' ] } }
    })).pop();
    log(result);

    mongoose.disconnect();

  } catch (e) {
    console.error(e);
  } finally {
    process.exit()
  }
})()

从 MongoDB 3.6 及更高版本开始，即使没有 $unwind 和 $group 构建：

const { Schema, Types: { ObjectId } } = mongoose = require('mongoose');

const uri = 'mongodb://localhost/looktest';

mongoose.Promise = global.Promise;
mongoose.set('debug', true);

const itemTagSchema = new Schema({
  tagName: String
});

const itemSchema = new Schema({
  title: String,
  description: String,
  tags: [{ type: Schema.Types.ObjectId, ref: 'ItemTag' }]
},{ timestamps: true });

itemSchema.statics.lookup = function({ path, query }) {
  let rel =
    mongoose.model(this.schema.path(path).caster.options.ref);

  // MongoDB 3.6 and up $lookup with sub-pipeline
  let pipeline = [
    { "$lookup": {
      "from": rel.collection.name,
      "as": path,
      "let": { [path]: `$${path}` },
      "pipeline": [
        { "$match": {
          ...query,
          "$expr": { "$in": [ "$_id", `$$${path}` ] }
        }}
      ]
    }}
  ];

  return this.aggregate(pipeline).exec().then(r => r.map(m =>
    this({ ...m, [path]: m[path].map(r => rel(r)) })
  ));
};

const Item = mongoose.model('Item', itemSchema);
const ItemTag = mongoose.model('ItemTag', itemTagSchema);

const log = body => console.log(JSON.stringify(body, undefined, 2));

(async function() {

  try {

    const conn = await mongoose.connect(uri);

    // Clean data
    await Promise.all(Object.entries(conn.models).map(([k,m]) => m.remove()));

    // Create tags and items
    const tags = await ItemTag.insertMany(
      ["movies", "funny"].map(tagName => ({ tagName }))
    );

    const item = await Item.create({
      "title": "Something",
      "description": "An item",
      tags
    });

    // Query with our static
    let result = (await Item.lookup({
      path: 'tags',
      query: { 'tagName': { '$in': [ 'funny', 'politics' ] } }
    })).pop();
    log(result);


    await mongoose.disconnect();

  } catch(e) {
    console.error(e)
  } finally {
    process.exit()
  }

})()