MongoDB投影数量大于2的文档 [英] MongoDB project the documents with count greater than 2
问题描述
我有一个类似
{
"_id": "201503110040020021",
"Line": "1", // several documents may have this Line value
"LineStart": ISODate("2015-03-11T06:49:35.000Z"),
"SSCEXPEND": [{
"Secuence": 10,
"Title": 1,
},
{
"Secuence": 183,
"Title": 613,
},
...
],
} {
"_id": "201503110040020022",
"Line": "1", // several documents may have this Line value
"LineStart": ISODate("2015-03-11T06:49:35.000Z"),
"SSCEXPEND": [{
"Secuence": 10,
"Title": 1,
},
],
}
SSCEXPEND是一个数组.我正在尝试计算SSC数组和项目的大小(如果计数大于或等于2).我的查询是这样的
SSCEXPEND is an array. I am trying to count the size of SSC array and project if the count is greater than or equal to 2. My query is something like this
db.entity.aggregate(
[
{
$project: {
SSCEXPEND_count: {$size: "$SSCEXPEND"}
}
},
{
$match: {
"SSCEXPEND_count2": {$gte: ["$SSCEXPEND_count",2]}
}
}
]
)
我希望输出仅是数组大小大于2的第一个文档.
I am expecting the output to be only the the first document whose array size is greater than 2.
项目部分工作正常,我能够获得计数,但是我只需要投影那些计数大于或等于2但我的匹配部分无效的项目.谁能指导我哪里出问题了?
Project part is working fine and I am able to get the counts but I need to project only those which has count greater than or equal to two but my match part is not working. Can any one guide me as where am I going wrong?
推荐答案
You need to project the other fields and your $match
pipeline will just need to do a query on the newly-created field to filter the documents based on the array size. Something like the following should work:
db.entity.aggregate([
{
"$project": {
"Line": 1,
"LineStart": 1, "SSCEXPEND": 1,
"SSCEXPEND_count": { "$size": "$SSCEXPEND" }
}
},
{
"$match": {
"SSCEXPEND_count": { "$gte": 2 }
}
}
])
示例输出:
/* 0 */
{
"result" : [
{
"_id" : "201503110040020021",
"Line" : "1",
"LineStart" : ISODate("2015-03-11T06:49:35.000Z"),
"SSCEXPEND" : [
{
"Secuence" : 10,
"Title" : 1
},
{
"Secuence" : 183,
"Title" : 613
}
],
"SSCEXPEND_count" : 2
}
],
"ok" : 1
}
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