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Aggregate.unwind

1. 接口描述#

功能: 使用指定的数组字段中的每个元素,对文档进行拆分。拆分后,文档会从一个变为一个或多个,分别对应数组的每个元素。

声明: 两种形式

  • 参数是一个字段名

unwind(<字段名>)

  • 参数是一个对象

unwind({ path: <字段名>, includeArrayIndex: <string>, preserveNullAndEmptyArrays: <boolean> })

2. 输入参数#

参数类型必填说明
pathstring想要拆分的数组的字段名,需要以 $ 开头。
includeArrayIndexstring可选项,传入一个新的字段名,数组索引会保存在这个新的字段上。新的字段名不能以 $ 开头。
preserveNullAndEmptyArraysboolean如果为 true,那么在 path 对应的字段为 null、空数组或者这个字段不存在时,依然会输出这个文档;如果为 falseunwind 将不会输出这些文档。默认为 false

3. 返回结果#

参数类型必填说明
-Aggregate聚合对象

4. 示例代码#

拆分数组#

假设我们有一个 products 集合,包含数据如下:

{ "_id": "1", "product": "tshirt", "size": ["S", "M", "L"] }{ "_id": "2", "product": "pants", "size": [] }{ "_id": "3", "product": "socks", "size": null }{ "_id": "4", "product": "trousers", "size": ["S"] }{ "_id": "5", "product": "sweater", "size": ["M", "L"] }

我们根据 size 字段对这些文档进行拆分

const tcb = require('@cloudbase/node-sdk')const app = tcb.init({  env: 'xxx'})
const db = app.database()
exports.main = async (event, context) => {  const res = await db    .collection('products')    .aggregate()    .unwind('$size')    .end()  console.log(res.data)}

输出如下:

{ "_id": "1", "product": "tshirt", "size": "S" }{ "_id": "1", "product": "tshirt", "size": "M" }{ "_id": "1", "product": "tshirt", "size": "L" }{ "_id": "4", "product": "trousers", "size": "S" }{ "_id": "5", "product": "sweater", "size": "M" }{ "_id": "5", "product": "sweater", "size": "L" }

拆分后,保留原数组的索引#

我们根据 size 字段对文档进行拆分后,想要保留原数组索引在新的 index 字段中。

const tcb = require('@cloudbase/node-sdk')const app = tcb.init({  env: 'xxx'})
const db = app.database()
exports.main = async (event, context) => {  const res = await db    .collection('products')    .aggregate()    .unwind({      path: '$size',      includeArrayIndex: 'index'    })    .end()  console.log(res.data)}

输出如下:

{ "_id": "1", "product": "tshirt", "size": "S", "index": 0 }{ "_id": "1", "product": "tshirt", "size": "M", "index": 1 }{ "_id": "1", "product": "tshirt", "size": "L", "index": 2 }{ "_id": "4", "product": "trousers", "size": "S", "index": 0 }{ "_id": "5", "product": "sweater", "size": "M", "index": 0 }{ "_id": "5", "product": "sweater", "size": "L", "index": 1 }

保留字段为空的文档#

注意到我们的集合中有两行特殊的空值数据:

...{ "_id": "2", "product": "pants", "size": [] }{ "_id": "3", "product": "socks", "size": null }...

如果想要在输出中保留 size 为空数组、null,或者 size 字段不存在的文档,可以使用 preserveNullAndEmptyArrays 参数

const tcb = require('@cloudbase/node-sdk')const app = tcb.init({  env: 'xxx'})
const db = app.database()
exports.main = async (event, context) => {  const res = await db    .collection('products')    .aggregate()    .unwind({      path: '$size',      preserveNullAndEmptyArrays: true    })    .end()  console.log(res.data)}

输出如下:

{ "_id": "1", "product": "tshirt", "size": "S" }{ "_id": "1", "product": "tshirt", "size": "M" }{ "_id": "1", "product": "tshirt", "size": "L" }{ "_id": "2", "product": "pants", "size": null }{ "_id": "3", "product": "socks", "size": null }{ "_id": "4", "product": "trousers", "size": "S" }{ "_id": "5", "product": "sweater", "size": "M" }{ "_id": "5", "product": "sweater", "size": "L" }