使用$ in在MongoDB中查找子文档 [英] Find sub-documents using $in with MongoDB
问题描述
我的任务是找到各个作者( comments.user_id
)评论文章( _id
)
{
_id:ObjectId(56479d9c8510369a4ecea3a9),
comments:[
{
text:222,
user_id:ObjectId(563f2db0e2bf6c431b297d45),
},
{
text:333 ,
user_id:ObjectId(563f2db0e2bf6c431b297d45),
},
{
text:444,
user_id:ObjectId 563f2db0e2bf6c431b297d45),
},
{
text:55555,
user_id:ObjectId(563e3337e2bf6c431b297d41),
},
{
text:00000,
user_id:ObjectId(563f7c0a8db7963420cd5732),
},
{
text: 00001,
user_id:ObjectId(563f7c0a8db7963420cd5732 ),
}
]
}
如下所示:
db.getCollection('messages')。find({
'_id':ObjectId(56479d9c8510369a4ecea3a9 ),
'comments.user_id':{$ in:[
ObjectId(563e3337e2bf6c431b297d41),
ObjectId(563f7c0a8db7963420cd5732)
]}
} )
它会返回所有注释。请帮助理解为什么会发生。
预期结果
{
_id:ObjectId(56479d9c8510369a4ecea3a9),
comments:[
{
text:55555,
user_id:ObjectId (563e3337e2bf6c431b297d41),
},
{
text:00000,
user_id:ObjectId(563f7c0a8db7963420cd5732),
},
{
text:00001,
user_id:ObjectId(563f7c0a8db7963420cd5732),
}
]
}
update query(hopelessness)
< code $ db.getCollection('messages')。find(
{'_id':ObjectId(56479d9c8510369a4ecea3a9)},
{'comments.user_id':{$ in:[ 563f2db0e2bf6c431b297d45,563e3337e2bf6c431b297d41]}},
{'comments.user_id':{$ elemMatch:{$ in:[563f2db0e2bf6c431b297d45,563e3337e2bf6c431b297d (''messages')。find(
{'_id':ObjectId(56479d9c8510369a4ecea3a9)} ,
{$ elemMatch:{'user_id':{$ in:[ObjectId(563f2db0e2bf6c431b297d45),ObjectId(563f7c0a8db7963420cd5732)]}}}}
)
我只返回1条记录,而且我有这些作者的所有记录
$ elemMatch
匹配的元素 要在您的投影中包含多个过滤的数组元素,注释
数组,您可以使用聚合
与 >:
db.getCollection('test')。aggregate([
{$ match :{
'_id':ObjectId(56479d9c8510369a4ecea3a9),
'comments.user_id':{$ in:[
ObjectId(563e3337e2bf6c431b297d41),
ObjectId 563f7c0a8db7963420cd5732)
]},
}},
{$ redact:{
$ cond:{
if:{
$ or:[
{$ eq:['$ user_id',ObjectId(563e3337e2bf6c431b297d41)]},
{$ eq:['$ user_id',ObjectId(563f7c0a8db7963420cd5732)]},
{ $ not:'$ user_id'}
]
},
then:'$$ DESCEND',
else:'$$ PRUNE'
}
}}
])
$ redact
遍历每一个文档,像一棵树,保存或修剪每个文档的字段,因为它是 $ cond
表达式指定的。
围绕 $ redact
包装头部有点棘手,但它基本上说,如果关卡的 user_id
字段与 $ in
中的两个ObjectId中的任何一个匹配,或者它不是目前(即因为它在文档的顶层)包含数据,否则删除它。
My task is to find individual authors(comments.user_id
) comment on the article (_id
)
{
"_id" : ObjectId("56479d9c8510369a4ecea3a9"),
"comments" : [
{
"text" : "222",
"user_id" : ObjectId("563f2db0e2bf6c431b297d45"),
},
{
"text" : "333",
"user_id" : ObjectId("563f2db0e2bf6c431b297d45"),
},
{
"text" : "444",
"user_id" : ObjectId("563f2db0e2bf6c431b297d45"),
},
{
"text" : "55555",
"user_id" : ObjectId("563e3337e2bf6c431b297d41"),
},
{
"text" : "00000",
"user_id" : ObjectId("563f7c0a8db7963420cd5732"),
},
{
"text" : "00001",
"user_id" : ObjectId("563f7c0a8db7963420cd5732"),
}
]
}
My query looks as follows
db.getCollection('messages').find({
'_id': ObjectId("56479d9c8510369a4ecea3a9"),
'comments.user_id': {$in : [
ObjectId("563e3337e2bf6c431b297d41"),
ObjectId("563f7c0a8db7963420cd5732")
]}
})
It returns all comments. Please help to understand why it happens.
Expected Result
{
"_id" : ObjectId("56479d9c8510369a4ecea3a9"),
"comments" : [
{
"text" : "55555",
"user_id" : ObjectId("563e3337e2bf6c431b297d41"),
},
{
"text" : "00000",
"user_id" : ObjectId("563f7c0a8db7963420cd5732"),
},
{
"text" : "00001",
"user_id" : ObjectId("563f7c0a8db7963420cd5732"),
}
]
}
update query (hopelessness)
db.getCollection('messages').find(
{'_id': ObjectId("56479d9c8510369a4ecea3a9")},
{'comments.user_id': {$in: ["563f2db0e2bf6c431b297d45", "563e3337e2bf6c431b297d41"]}},
{'comments.user_id': {$elemMatch: {$in: ["563f2db0e2bf6c431b297d45", "563e3337e2bf6c431b297d41"]}}}
)
db.getCollection('messages').find(
{'_id': ObjectId("56479d9c8510369a4ecea3a9")},
{comments: {$elemMatch: {'user_id': {$in : [ObjectId("563f2db0e2bf6c431b297d45"), ObjectId("563f7c0a8db7963420cd5732")]}}}}
)
I return only 1 record, and I have all the records from these authors
As you've seen, the $
and $elemMatch
projection operators only include the first matching element.
To include multiple, filtered array elements in your projection of the comment
array, your can use aggregate
with the $redact
operator instead of find
:
db.getCollection('test').aggregate([
{$match: {
'_id': ObjectId("56479d9c8510369a4ecea3a9"),
'comments.user_id': {$in : [
ObjectId("563e3337e2bf6c431b297d41"),
ObjectId("563f7c0a8db7963420cd5732")
]},
}},
{$redact: {
$cond: {
if: {
$or: [
{$eq: ['$user_id', ObjectId("563e3337e2bf6c431b297d41")]},
{$eq: ['$user_id', ObjectId("563f7c0a8db7963420cd5732")]},
{$not: '$user_id'}
]
},
then: '$$DESCEND',
else: '$$PRUNE'
}
}}
])
$redact
iterates over each doc like a tree, keeping or trimming the fields of each doc as it's $cond
expression dictates.
It gets a bit tricky to wrap your head around $redact
, but it's basically saying that if the level's user_id
field matches either of the two ObjectIds in your $in
, or it's not present (i.e. as it is in the top level of the doc), include the data, otherwise remove it.
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