mongodb 聚合中的 $replaceRoot [英] $replaceRoot in mongodb aggregation
本文介绍了mongodb 聚合中的 $replaceRoot的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我有一个这样的集合:
{
"_id" : ObjectId("5bd1686ba64b9206349284db"),
"type" : "Package",
"codeInstances" : [
{
"name" : "a",
"description" : "a"
},
{
"name" : "b",
"description" : "b1"
},
{
"name" : "b",
"description" : "b2"
}
]
}
{
"_id" : ObjectId("5bd16ab8a64b92068d485054"),
"type" : "Package",
"codeInstances" : [
{
"name" : "a",
"description" : "a"
},
{
"name" : "b",
"description" : "b3"
}
]
}
以下结构是我想要的:
{
"name" : "b",
"description" : "b1"
},
{
"name" : "b",
"description" : "b1"
},
{
"name" : "b",
"description" : "b3"
}
我尝试了这个聚合操作:
I tried this aggregate operations:
db.getCollection('t_system_code').aggregate([
{"$unwind":"$codeInstances"},
{$match:{"codeInstances.name":"b","type" : "Package"}},
{"$project":{"codeInstances":1,"_id":0}}
]);
但这不是我想要的结构:
But thatundefineds not the structure I want:
{
"codeInstances" : {
"name" : "b",
"description" : "b1"
}
}
{
"codeInstances" : {
"name" : "b",
"description" : "b2"
}
}
{
"codeInstances" : {
"name" : "b",
"description" : "b3"
}
}
帮助.谢谢.
推荐答案
您可以使用 $replaceRoot
db.collection.aggregate([
{ "$match": { "codeInstances.name": "b", "type": "Package" }},
{ "$unwind": "$codeInstances" },
{ "$match": { "codeInstances.name": "b", "type": "Package" }},
{ "$replaceRoot": { "newRoot": "$codeInstances" }}
])
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