如何找到数组mongodb的长度 [英] How to find length of the array mongodb
本文介绍了如何找到数组mongodb的长度的处理方法,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
我的数据库有这种类型的结构.我想找到我的JAN"数组包含的文档数量.我正在尝试以不同的方式做,但没有任何效果.如果有人帮忙那就太好了.
I have such this type of structure of my database. I want to find number of documents my "JAN" array contains. I am trying to do in different way but nothing works. That would be great if someone helps.
{
"_id" : ObjectId("5cd8609db20663a19e2c362c"),
"2017" : {
"JAN" : [
{
"SYMBOL" : "20MICRONS",
"SERIES" : "EQ",
"OPEN" : "33.4",
"HIGH" : "34.3",
"LOW" : "33",
},
{
"SYMBOL" : "3IINFOTECH",
"SERIES" : "EQ",
"OPEN" : "5.8",
"HIGH" : "5.8",
"LOW" : "5.55",
},
{
"SYMBOL" : "3MINDIA",
"SERIES" : "EQ",
"OPEN" : "11199.9",
"HIGH" : "11233",
"LOW" : "10861",
}
]
}
}
推荐答案
您可以使用 $size
运算符求数组的长度
You can use $size
operator to find the length of the array
db.collection.aggregate([
{
"$project": {
"totalJan": {
"$size": "$2017.JAN"
}
}
}
])
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