Mongodb 数组连接

Question

在查询mongodb时，是否可以对结果进行处理(“project”)，从而进行数组拼接？我实际上有 2 种不同的情况:

(1) 来自不同领域的数组:，例如:

Given:
{companyName:'microsoft', managers:['ariel', 'bella'], employees:['charlie', 'don']}
{companyName:'oracle',   managers:['elena', 'frank'], employees:['george', 'hugh']}

I'd like my query to return each company with its 'managers' and 'employees' concatenated:
{companyName:'microsoft', allPersonnel:['ariel', 'bella','charlie', 'don']}
{companyName:'oracle',   allPersonnel:['elena', 'frank','george', 'hugh']}

(2) 嵌套数组:，例如:

Given the following docs, where employees are separated into nested arrays (never mind why, it's a long story):
{companyName:'microsoft', personnel:[ ['ariel', 'bella'], ['charlie', 'don']}
{companyName:'oracle',   personnel:[ ['elena', 'frank'], ['george', 'hugh']}

I'd like my query to return each company with a flattened 'personal' array:
{companyName:'microsoft', allPersonnel:['ariel', 'bella','charlie', 'don']}
{companyName:'oracle',   allPersonnel:['elena', 'frank','george', 'hugh']}

如果有任何想法，请使用“查找”或“聚合”非常感谢:)

Answer 1

当然，在现代 MongoDB 版本中，我们可以简单地使用 $concatArrays这里:

db.collection.aggregate([
  { "$project": {
    "companyNanme": 1,
    "allPersonnel": { "$concatArrays": [ "$managers", "$employees" ] }
  }}
])

或者对于带有嵌套数组的第二种形式，使用 $reduce组合:

db.collection.aggregate([
  { "$project": {
    "companyName": 1,
    "allEmployees": {
      "$reduce": {
        "input": "$personnel",
        "initialValue": [],
        "in": { "$concatArrays": [ "$$value", "$$this" ] }
      }
    }
  }}
])

---

有 $setUnion聚合框架可用的运算符。这里的约束是这些是“集合”，并且所有成员实际上都是“唯一的”，因为“集合”要求:

db.collection.aggregate([
    { "$project": {
        "companyname": 1,
        "allPersonnel": { "$setUnion": [ "$managers", "$employees" ] }
    }}
])

所以这很酷，只要所有都是“唯一的”并且你在奇异数组中。

在替代情况下，您始终可以使用 $unwind 和 $group 进行处理。人员嵌套数组是一个简单的双重展开

db.collection.aggregate([
   { "$unwind": "$personnel" },
   { "$unwind": "$personnel" },
   { "$group": {
       "_id": "$_id",
       "companyName": { "$first": "$companyName" },
       "allPersonnel": { "$push": { "$personnel" } }
   }}
])

或者与第一个早于 MongoDB 2.6 的版本相同，其中“集合运算符”不存在:

db.collection.aggregate([
    { "$project": {
        "type": { "$const": [ "M", "E" ] },
        "companyName": 1,
        "managers": 1,
        "employees": 1
    }},
    { "$unwind": "$type" },
    { "$unwind": "$managers" },
    { "$unwind": "$employees" },
    { "$group": {
        "_id": "$_id",
       "companyName": { "$first": "$companyName" },
       "allPersonnel": {
           "$addToSet": {
               "$cond": [
                   { "$eq": [ "$type", "M" ] },
                   "$managers",
                   "$employees"
               ]
           }
       }
    }}
])