在MongoDB中添加组计数器和项计数器？
在MongoDB中添加组计数器和项计数器？
提问于 2020-09-01 14:20:37
我有个Json：
[
{
"key": "guitar",
"name": "john"
},
{
"key": "guitar",
"name": "paul"
},
{
"key": "guitar",
"name": "george"
},
{
"key": "drums",
"name": "ringo"
}
]让我们按key分组并将项添加到每个组中：
db.collection.aggregate([
{
$sort: {
name: -1
}
},
{
$group: {
_id: "$key",
"projects": {
"$push": "$$ROOT"
},
count: {
$sum: 1
}
}
},
{
$sort: {
"_id": 1
}
}
])结果：
[
{
"_id": "drums",
"count": 1,
"projects": [
{
"_id": ObjectId("5a934e000102030405000003"),
"key": "drums",
"name": "ringo"
}
]
},
{
"_id": "guitar",
"count": 3,
"projects": [
{
"_id": ObjectId("5a934e000102030405000001"),
"key": "guitar",
"name": "paul"
},
{
"_id": ObjectId("5a934e000102030405000000"),
"key": "guitar",
"name": "john"
},
{
"_id": ObjectId("5a934e000102030405000002"),
"key": "guitar",
"name": "george"
}
]
}
]问题：
如何添加这样的计数器：
[
{
"_id": "drums",
"Counter":0, // <--------------------------------
"count": 1,
"projects": [
{
"_id": ObjectId("5a934e000102030405000003"),
"key": "drums",
"name": "ringo",
"InnerCounter":0 // <--------------------------------
}
]
},
{
"_id": "guitar",
"Counter":1, // <--------------------------------
"count": 3,
"projects": [
{
"_id": ObjectId("5a934e000102030405000001"),
"key": "guitar",
"name": "paul",
"InnerCounter":0 // <--------------------------------
},
{
"_id": ObjectId("5a934e000102030405000000"),
"key": "guitar",
"name": "john",
"InnerCounter":1 // <--------------------------------
},
{
"_id": ObjectId("5a934e000102030405000002"),
"key": "guitar",
"name": "george",
"InnerCounter":2 // <--------------------------------
}
]
}
]回答 1
Stack Overflow用户
发布于 2020-09-01 15:01:09
我认为没有其他选项可以这样做，您可以尝试使用$unwind来使用includeArrayIndex属性在数组中创建索引字段，
db.collection.aggregate([
{ $sort: { name: -1 } },
{
$group: {
_id: "$key",
projects: { $push: "$$ROOT" }
}
},
// $unwind "projects" array and store index in field "projects.InnerCounter"
{
$unwind: {
path: "$projects",
includeArrayIndex: "projects.InnerCounter"
}
},
// again group by _id and reconstruct "projects" array
{
$group: {
_id: "$_id",
projects: { $push: "$projects" },
count: { $sum: 1 }
}
},
// sort by "_id"
{ $sort: { "_id": 1 } },
// group by $$ROOT and construct root array
{
$group: {
_id: null,
root: { $push: "$$ROOT" }
}
},
// deconstruct root array and add field "Counter" ofr index counter
{
$unwind: {
path: "$root",
includeArrayIndex: "root.Counter"
}
},
// replace to root
{ $replaceRoot: { newRoot: "$root" } }
])projects数组没有$unwind的另一个选项，
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/63689580
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