Mongoose 中的 Aggregate 介绍-技术鸭(jishuya.cn)

Mongoose的 aggregate()函数是您如何将 MongoDB 的Aggregation Framework 与 Mongoose 一起使用。 Mongoose的 aggregate()中工作的任何聚合查询都 MongoDB shell 应该在 Mongoose 中工作，无需任何更改。

什么是 Aggregation Framework ？

从语法上讲，Aggregation Framework 查询是一系列阶段。阶段是 MongoDB 如何转换进入阶段的任何文档的对象描述第一阶段将文档馈送到第二阶段，依此类推，因此您可以使用阶段组合转换。您传递给的阶段数组 aggregate() 函数称为聚合管道。

`$match` 阶段

$match 阶段过滤掉与给定不匹配的文档 filter 参数，类似于 Mongoose 的 find() 功能。


<code class="language-javascript">await Character.create([
  { name: Jean-Luc Picard, age: 59, rank: Captain },
  { name: William Riker, age: 29, rank: Commander },
  { name: Deanna Troi, age: 28, rank: Lieutenant Commander },
  { name: Geordi La Forge, age: 29, rank: Lieutenant },
  { name: Worf, age: 24, rank: Lieutenant }
]);
const filter = { age: { $gte: 30 } };
let docs = await Character.aggregate([
  { $match: filter }
]);
docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59
// `$match` is similar to `find()`
docs = await Character.find(filter);
docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59</code>
<code class="language-javascript">await Character.create([
  { name: Jean-Luc Picard, age: 59, rank: Captain },
  { name: William Riker, age: 29, rank: Commander },
  { name: Deanna Troi, age: 28, rank: Lieutenant Commander },
  { name: Geordi La Forge, age: 29, rank: Lieutenant },
  { name: Worf, age: 24, rank: Lieutenant }
]);

const filter = { age: { $gte: 30 } };
let docs = await Character.aggregate([
  { $match: filter }
]);

docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59

// `$match` is similar to `find()`
docs = await Character.find(filter);
docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59</code>
await Character.create([
  { name: Jean-Luc Picard, age: 59, rank: Captain },
  { name: William Riker, age: 29, rank: Commander },
  { name: Deanna Troi, age: 28, rank: Lieutenant Commander },
  { name: Geordi La Forge, age: 29, rank: Lieutenant },
  { name: Worf, age: 24, rank: Lieutenant }
]);
const filter = { age: { $gte: 30 } };
let docs = await Character.aggregate([
  { $match: filter }
]);
docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59
// `$match` is similar to `find()`
docs = await Character.find(filter);
docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59
await Character.create([
  { name: Jean-Luc Picard, age: 59, rank: Captain },
  { name: William Riker, age: 29, rank: Commander },
  { name: Deanna Troi, age: 28, rank: Lieutenant Commander },
  { name: Geordi La Forge, age: 29, rank: Lieutenant },
  { name: Worf, age: 24, rank: Lieutenant }
]);

const filter = { age: { $gte: 30 } };
let docs = await Character.aggregate([
  { $match: filter }
]);

docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59

// `$match` is similar to `find()`
docs = await Character.find(filter);
docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59
await Character.create([
  { name: Jean-Luc Picard, age: 59, rank: Captain },
  { name: William Riker, age: 29, rank: Commander },
  { name: Deanna Troi, age: 28, rank: Lieutenant Commander },
  { name: Geordi La Forge, age: 29, rank: Lieutenant },
  { name: Worf, age: 24, rank: Lieutenant }
]);

const filter = { age: { $gte: 30 } };
let docs = await Character.aggregate([
  { $match: filter }
]);

docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59

// `$match` is similar to `find()`
docs = await Character.find(filter);
docs.length; // 1
docs[0].name; // Jean-Luc Picard
docs[0].age // 59

`$group` 阶段

聚合可以做的不仅仅是过滤文档。您还可以使用Aggregation Framework 来转换文档。例如 $group 舞台表现得像 reduce() 功能。例如 $group stage 让您计算给定的字符数 age。


<code class="language-javascript">let docs = await Character.aggregate([
  {
    $group: {
      // Each `_id` must be unique, so if there are multiple
      // documents with the same age, MongoDB will increment `count`.
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);
docs.length; // 4
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
docs[3]; // { _id: 59, count: 1 }</code>
<code class="language-javascript">let docs = await Character.aggregate([
  {
    $group: {
      // Each `_id` must be unique, so if there are multiple
      // documents with the same age, MongoDB will increment `count`.
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);

docs.length; // 4
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
docs[3]; // { _id: 59, count: 1 }</code>
let docs = await Character.aggregate([
  {
    $group: {
      // Each `_id` must be unique, so if there are multiple
      // documents with the same age, MongoDB will increment `count`.
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);
docs.length; // 4
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
docs[3]; // { _id: 59, count: 1 }
let docs = await Character.aggregate([
  {
    $group: {
      // Each `_id` must be unique, so if there are multiple
      // documents with the same age, MongoDB will increment `count`.
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);

docs.length; // 4
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
docs[3]; // { _id: 59, count: 1 }
let docs = await Character.aggregate([
  {
    $group: {
      // Each `_id` must be unique, so if there are multiple
      // documents with the same age, MongoDB will increment `count`.
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);

docs.length; // 4
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
docs[3]; // { _id: 59, count: 1 }

结合多个阶段

聚合管道的优势在于它的可组合性。例如您可以结合前面的两个示例，仅按以下方式对字符进行分组 age 如果他们的 age 是 < 30。


<code class="language-javascript">let docs = await Character.aggregate([
  { $match: { age: { $lt: 30 } } },
  {
    $group: {
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);
docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }</code>
<code class="language-javascript">let docs = await Character.aggregate([
  { $match: { age: { $lt: 30 } } },
  {
    $group: {
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }</code>
let docs = await Character.aggregate([
  { $match: { age: { $lt: 30 } } },
  {
    $group: {
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);
docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
let docs = await Character.aggregate([
  { $match: { age: { $lt: 30 } } },
  {
    $group: {
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
let docs = await Character.aggregate([
  { $match: { age: { $lt: 30 } } },
  {
    $group: {
      _id: $age,
      count: { $sum: 1 }
    }
  }
]);

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }

Mongoose `Aggregate` Class

Mongoose 的 aggregate() 函数返回一个 Mongoose 的实例 Aggregate 类。Aggregate实例是 thenable ，因此您可以将它们与 await 和承诺链接。

Aggregate 类还支持用于构建聚合管道的链接接口。例如，下面的代码显示了构建聚合管道的另一种语法 $match 其次是 $group。


<code class="language-javascript">let docs = await Character.aggregate().
  match({ age: { $lt: 30 } }).
  group({ _id: $age, count: { $sum: 1 } });
docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }</code>
<code class="language-javascript">let docs = await Character.aggregate().
  match({ age: { $lt: 30 } }).
  group({ _id: $age, count: { $sum: 1 } });

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }</code>
let docs = await Character.aggregate().
  match({ age: { $lt: 30 } }).
  group({ _id: $age, count: { $sum: 1 } });
docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
let docs = await Character.aggregate().
  match({ age: { $lt: 30 } }).
  group({ _id: $age, count: { $sum: 1 } });

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
let docs = await Character.aggregate().
  match({ age: { $lt: 30 } }).
  group({ _id: $age, count: { $sum: 1 } });

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }

Mongoose 中间件也支持 pre(aggregate) 和 post(aggregate)钩子。您可以使用聚合中间件来转换聚合管道。


<code class="language-javascript">const characterSchema = Schema({ name: String, age: Number });
characterSchema.pre(aggregate, function() {
  // Add a `$match` to the beginning of the pipeline
  this.pipeline().unshift({ $match: { age: { $lt: 30 } } });
});
const Character = mongoose.model(Character, characterSchema);
// The `pre(aggregate)` adds a `$match` to the pipeline.
let docs = await Character.aggregate().
  group({ _id: $age, count: { $sum: 1 } });
docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }</code>
<code class="language-javascript">const characterSchema = Schema({ name: String, age: Number });
characterSchema.pre(aggregate, function() {
  // Add a `$match` to the beginning of the pipeline
  this.pipeline().unshift({ $match: { age: { $lt: 30 } } });
});
const Character = mongoose.model(Character, characterSchema);

// The `pre(aggregate)` adds a `$match` to the pipeline.
let docs = await Character.aggregate().
  group({ _id: $age, count: { $sum: 1 } });

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }</code>
const characterSchema = Schema({ name: String, age: Number });
characterSchema.pre(aggregate, function() {
  // Add a `$match` to the beginning of the pipeline
  this.pipeline().unshift({ $match: { age: { $lt: 30 } } });
});
const Character = mongoose.model(Character, characterSchema);
// The `pre(aggregate)` adds a `$match` to the pipeline.
let docs = await Character.aggregate().
  group({ _id: $age, count: { $sum: 1 } });
docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
const characterSchema = Schema({ name: String, age: Number });
characterSchema.pre(aggregate, function() {
  // Add a `$match` to the beginning of the pipeline
  this.pipeline().unshift({ $match: { age: { $lt: 30 } } });
});
const Character = mongoose.model(Character, characterSchema);

// The `pre(aggregate)` adds a `$match` to the pipeline.
let docs = await Character.aggregate().
  group({ _id: $age, count: { $sum: 1 } });

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }
const characterSchema = Schema({ name: String, age: Number });
characterSchema.pre(aggregate, function() {
  // Add a `$match` to the beginning of the pipeline
  this.pipeline().unshift({ $match: { age: { $lt: 30 } } });
});
const Character = mongoose.model(Character, characterSchema);

// The `pre(aggregate)` adds a `$match` to the pipeline.
let docs = await Character.aggregate().
  group({ _id: $age, count: { $sum: 1 } });

docs.length; // 3
docs.sort((d1, d2) => d1._id - d2._id);
docs[0]; // { _id: 24, count: 1 }
docs[1]; // { _id: 28, count: 1 }
docs[2]; // { _id: 29, count: 2 }