{
"_id" : ObjectId("5da7c114753c6202f4f4d3b2"),
"image" : "hem sopheap-1571275028119.jpg",
"body" : "my first post\r\nyes this my post",
"date" : ISODate("2019-10-17T00:59:18.901Z"),
"comments" : [
{
"user" : "5d999578aeb073247de4bd6e",
"fullname" : "hem sopheap",
"username" : "sopheap",
"comment" : "My first comment",
"_id" : ObjectId("5da7c125753c6202f4f4d3b4"),
"replies" : []
},
{
"user" : "5da85558886aee13e4e7f044",
"fullname" : "soeng kanel",
"username" : "",
"comment" : "Mr. kansael comment",
"_id" : ObjectId("5da8557f886aee13e4e7f045"),
"replies" : [],
"date" : ISODate("2019-10-17T10:10:37.394Z"),
"likes" : [
"5d999578aeb073247de4bd6e",
"5d999578aeb073247de4bd6f"
]
}
],
"__v" : 41,
"likes" : [
"5d999578aeb073247de4bd6e",
"5d999578aeb073247de4bd6p"
]
}
我想获得的所有likes特定的comments不喜欢的post在SQL语句中类似这样的：
db.posts.find({
"comments": {
$elemMatch: {
"_id": ObjectId("5da8557f886aee13e4e7f045")
}
}
}, {
likes:"$comments", _id:0
}).pretty()
和预期的结果应该是这样的
"likes" : [ "5d999578aeb073247de4bd6e", "5d999578aeb073247de4bd6f" ]
这是您的完整查询
db.posts.find({
"comments": {
$elemMatch: {
"user": "5da85558886aee13e4e7f044",
"_id": ObjectId("5da8557f886aee13e4e7f045")
}
}
}, {
likes:"$comments.likes", _id:0
}).pretty()解释：
人们在基于数组子文档的多个字段进行过滤时犯的一个常见错误是简单地执行类似的操作{"comments._id": "something", "comments.user": "something"}，即在某些项目与 id、user 匹配的地方返回数组子文档的所有项目。这个问题的解决方案是$elemMatch
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