因此,我正在学习mongodb,并且得到了一些作家培训。在这里,我试图通过按作者的国家和性别来对作品进行计数。到目前为止,这是我实现的目标:
db.writers.aggregate([
{ "$match": { "gender": {"$ne": male}}},
{ "$group": {
"_id": {
"country_id": "$country_id",
"type": "$type"
},
}},
{ "$group": {
"_id": "$_id.country_id",
"literary_work": {
"$push": {
"type": "$_id.type",
"count": { "$sum": "$type" }
}
},
"total": { "$sum": "$type" }
}},
{ "$sort": { "country_id": 1 } },
{ "$project": {
"literary_work": { "$slice": [ "$literary_work", 3 ] },
"total": { "$sum": "$type" }
}}
])
可悲的是,我得到的输出不是我期望的:
"_id" : GREAT BRITAIN,
"literary_work" : [
{
"type" : "POEM",
"count" : 0
},
{
"type" : "NOVEL",
"count" : 0
},
{
"type" : "SHORT STORY",
"count" : 0
}
],
"total" : 0
谁能告诉我在哪里插入计数阶段或我的错误是什么?)
更新:
数据样本:
{
"_id" : ObjectId("5f115c5d5f62f9f482cd7a49"),
"author" : George Sand,
"gender" : female,
"country_id" : FRANCE,
"title": "Consuelo",
"type" : "NOVEL",
}
预期结果(注意!这是两个性别的结果):
{
"_id" : FRANCE,
"count" : 59.0,
"literary_work" : [
{
"type" : "POEM",
"count" : 14.0
},
{
"type" : "NOVEL",
"count" : 34.0
},
{
"type" : "SHORT STORY",
"count" : 11.0
}
]
}
您的实现是正确的方法,但是缺少一些东西:
$group
literary_work
$project
不需要您的查询更正查询中的内容,
db.writers.aggregate([
{
$match: {
gender: { $ne: "male" }
}
},
{
$group: {
_id: {
country_id: "$country_id",
type: "$type"
},
// missed this
count: { $sum: 1 }
}
},
{
$group: {
_id: "$_id.country_id",
// this count will be on the base of first group count
count: { $sum: "$count" },
literary_work: {
$push: {
type: "$_id.type",
// add count in inner count
count: "$count"
}
}
}
},
// corrected from country_id to _id
{
$sort: { "_id": 1 }
}
])
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