如何按字段对文档进行分组并使用带有 CouchDB 视图的自定义 reduce 函数列出不相等的值

Posted 2023-03-16

【中文标题】如何按字段对文档进行分组并使用带有 CouchDB 视图的自定义 reduce 函数列出不相等的值

【英文标题】：How to group documents by a field and list unequal values with custom reduce function with CouchDB view

【发布时间】：2019-09-09 02:09:37

【问题描述】：

我在 CouchDB 中有 1000 份员工文档，简化格式如下所示：

    "_id": "1111",
    "departmentId": "dept_A",
    "siteId": "SITE_1"


    "_id": "2222",
    "departmentId": "dept_B",
    "siteId": "SITE_1"


    "_id": "3333",
    "departmentId": "dept_C",
    "siteId": "SITE_1"


    "_id": "4444",
    "departmentId": "dept_C",
    "siteId": "SITE_1"


    "_id": "5555",
    "departmentId": "dept_A",
    "siteId": "SITE_2"


    "_id": "6666",
    "departmentId": "dept_A",
    "siteId": "SITE_2"

我有这样的看法：

function (doc) 
    if (doc.departmentId && doc.siteId) 
        emit(doc.siteId, doc.departmentId);
    

这将像这样显示数据：

"SITE_1": "dept_A"
"SITE_1": "dept_B"
"SITE_1": "dept_C"
"SITE_1": "dept_C"
"SITE_2": "dept_A"
"SITE_2": "dept_A"

但是，我想使用带有 CouchDB 视图的自定义 reduce 函数来对数据进行分组，如下所示：

"SITE_1": ["dept_A", "dept_B", "dept_C"]
"SITE_2": ["dept_A"]

CouchDB 视图的自定义 reduce 函数如下所示：

function (keys, values, rereduce) 

【问题讨论】：

siteId: 1 未包含在您的输出中是拼写错误还是您没有按任何规则添加？

错字感谢现场

【参考方案1】：

您可以使用reduce 和Set

let arr= ["_id": "1111","departmentId": "dept_A","siteId": "SITE_1","_id": "2222","departmentId": "dept_B","siteId": "SITE_1","_id": "3333","departmentId": "dept_C","siteId": "SITE_1","_id": "4444","departmentId": "dept_C","siteId": "SITE_1","_id": "5555","departmentId": "dept_A","siteId": "SITE_2","_id": "6666","departmentId": "dept_A","siteId": "SITE_2"]

let final = arr.reduce((op, siteId, departmentId) => 
  op[siteId] = op[siteId] || new Set()
  op[siteId].add(departmentId)
  return op
,)

console.log(...final['SITE_1'])
console.log(...final['SITE_2'])

【讨论】：

这个 js 对于 CouchDB reduce 来说太现代了。它不适用于“let”等。

@xpqz 这个代码可以很容易地转换成for循环和var这种情况