Arangodb AQL 连接、合并、嵌入嵌套的三个或更多集合

Question

我有以下集合，基于示例 Arangodb doc here，但添加了第三个名为 region 的集合

Users
{ 
  "name" : { 
    "first" : "John", 
    "last" : "Doe" 
  }, 
  "city" : "cities/2241300989", 
  "_id" : "users/2290649597", 
  "_rev" : "2290649597", 
  "_key" : "2290649597" 
}

Cities
{ 
  "population" : 1000, 
  "name" : "Metropolis", 
  "region" : "regions/2282300990", 
  "_id" : "cities/2241300989", 
  "_rev" : "2241300989", 
  "_key" : "2241300989" 
}


Regions
{  
  "name" : "SomeRegion1", 
  "_id" : "regions/2282300990", 
  "_rev" : "2282300990", 
  "_key" : "2282300990" 
} 

我想要一个像这样的目标结果

[ 
  { 
    "user" : { 
      "name" : { 
        "first" : "John", 
        "last" : "Doe" 
      }, 
      "_id" : "users/2290649597", 
      "_rev" : "2290649597", 
      "_key" : "2290649597" 
    }, 
    "city" : { 
      "population" : 1000, 
      "name" : "Metropolis",
      "_id" : "cities/2241300989", 
      "_rev" : "2241300989", 
      "_key" : "2241300989",
      "region" : {
          "name" : "SomeRegion1", 
          "_id" : "regions/2282300990", 
          "_rev" : "2282300990", 
          "_key" : "2282300990" 
      }
    } 
  } 
]

Arangodb 文档here 中的示例只有两个集合的查询

FOR u IN users 
    FOR c IN cities 
        FILTER u.city == c._id  RETURN merge(u, {city: c})

# However I want to have more than two collections e.g.
FOR u IN users 
  FOR c IN cities 
    For r IN regions
      FILTER u.city == c._id and c.region == r._id RETURN merge(????????)

如上加入三个集合，您将如何获得结果？如果我想要第四个嵌套的会怎样？

Answer 1

当您存储引用另一个集合的文档 _id 时，您可以利用 DOCUMENT AQL 命令。

所以你的 AQL 查询变得更简单了，像这样：

FOR u IN users
  LET city = DOCUMENT(u.city)
  LET city_with_region = MERGE(city, { region: DOCUMENT(city.region})
  RETURN MERGE(u, { city: city_with_region})

这个查询可以折叠得更多，但我把它留成这样，这样它就更能自我记录了。

DOCUMENT 的酷之处在于您只能返回文档的单个属性，例如 LET region_name = DOCUMENT(city.region).name。

我还发现，在大多数情况下，执行子查询来定位文档的性能更高。

Answer 2

大概是这样的：

FOR u IN users 
  FOR c IN cities 
    For r IN regions
      FILTER u.city == c._id AND c.region == r._id
      RETURN { user: u, city: MERGE(c, {region: r } }

您存储 id 而不是键来引用城市和地区是否有特殊原因？ _id 只是一个虚拟字段，由集合名称前缀的 _key 组成（加上一个斜杠）。所以这同样有效（我故意省略了内部的 _id 和 _rev 字段）：

Users
{ 
  "name" : { 
    "first" : "John", 
    "last" : "Doe" 
  }, 
  "city" : "2241300989", 
  "_key" : "2290649597"
}

Cities
{ 
  "population" : 1000, 
  "name" : "Metropolis", 
  "region" : "2282300990",
  "_key" : "2241300989" 
}


Regions
{  
  "name" : "SomeRegion1",
  "_key" : "2282300990"
}

FOR u IN users 
  FOR c IN cities 
    For r IN regions
      FILTER u.city == c._key AND c.region == r._key
      RETURN { user: u, city: MERGE(c, {region: r } }