Question

鉴于以下文件：

{"classes":3,
"people" : [

    {name:John,
    age:20,
    city:London}

    {name:Alice,
    age:56,
    city:Dublin}

]
}

我的数据库中有很多这样的文档。我只想选择数组中的第一个子文档（此处为John），然后根据第一个子文档中人员的年龄对所有文档进行排序。我还想只选择类数大于零的整体文档。我想创建一个排序元组，每个文档中第一个人的年龄，这是我的想法开始：

sorted([(m['age'], m) for m in people.find({"classes":{'$gt':0}},{'people.1':1}  )])

感谢您的帮助。

Answer 1

尝试使用pymongo驱动程序排序（您还可以使用pymongo的DESCENDING方法的ASCENDING和sort参数来控制排序方向：

from pymongo import DESCENDING
people = db.people.find({"classes": {'$gt': 0}}).sort('people.0.age', DESCENDING)

然后使用python创建元组列表。

[(p['people'][0]['age'], p) for p in people]

希望我能正确理解你的问题。

Answer 2

出于性能原因，您应该在Mongo而不是Python中进行选择和排序。我不知道你是否想要整个子文档在元组中或只是年龄，但这是你将如何做到这一点。

示例数据：

> db.tuple.find({},{_id:0})
{ "classes" : 3, "people" : [   {   "name" : "John",    "age" : 20,     "city" : "London" },    {   "name" : "Alice",   "age" : 56,     "city" : "Dublin" } ] }
{ "classes" : 3, "people" : [   {   "name" : "John",    "age" : 50,     "city" : "London" },    {   "name" : "Alice",   "age" : 56,     "city" : "Dublin" } ] }
{ "classes" : 3, "people" : [   {   "name" : "John",    "age" : 10,     "city" : "London" },    {   "name" : "Alice",   "age" : 56,     "city" : "Dublin" } ] }
{ "classes" : 0, "people" : [   {   "name" : "John",    "age" : 10,     "city" : "London" },    {   "name" : "Alice",   "age" : 56,     "city" : "Dublin" } ] }
{ "people" : [  {   "name" : "John",    "age" : 15,     "city" : "London" },    {   "name" : "Alice",   "age" : 56,     "city" : "Dublin" } ] }

返回按类年龄排序的第一个数组文档＆gt; 0：

> db.tuple.find({classes:{$gt:0}}, {_id:0,"people":1,"people":{$slice:1}}).sort({"people.age":1})
{ "classes" : 3, "people" : [ { "name" : "John", "age" : 10, "city" : "London" } ] }
{ "classes" : 3, "people" : [ { "name" : "John", "age" : 20, "city" : "London" } ] }
{ "classes" : 3, "people" : [ { "name" : "John", "age" : 50, "city" : "London" } ] }

返回年龄的同样的事情：

> db.tuple.find({classes:{$gt:0}}, {_id:0,"people.age":1,"people":{$slice:1}}).sort({"people.age":1})
{ "people" : [ { "age" : 10 } ] }
{ "people" : [ { "age" : 20 } ] }
{ "people" : [ { "age" : 50 } ] }

在Mongo中选择子文档

2 个答案: