[英]get _id based on value from a collection for a array and insert in mongodb collection
Input:输入:
[{"gradeName":1,"sectionName":"a","maximumStudents":12},{"gradeName":2,"sectionName":"b","maximumStudents":13}]
In mongodb how to get the _id of gradeName and sectionName from two collection and store in the third collection say mergeddetails在mongodb中如何从两个集合中获取gradeName和sectionName的_id并存储在第三个集合中说mergeddetails
mergeddetails:合并详情:
[{"grade_id":"60f819e04a9d43158cabad55","section_id":"60f819e04a9d43158cabad54","maximumStudents":12},{"grade_id":"60f819e04a9d43158cabad59","section_id":"60f819e04a9d43158cabad5b","maximumStudents":13}]
where grade_id is the _id of corresponding gradeName,section_id is the _id of corresponding sectionName please help with with mongodb quire i am using nodejs to write the API其中grade_id是对应gradeName的_id,section_id是对应sectionName的_id请帮助mongodb quire我正在使用nodejs编写API
You need to use $lookup
for both the collections您需要对这两个集合使用
$lookup
db.student.aggregate([
{ $lookup:
{ from: "grade",
localField: "gradeName",
foreignField: "grade",
as: "grade"
}
},
{$lookup:
{ from: "section",
localField: "sectionName",
foreignField: "section",
as: "section"
}
},
{ $unwind: "$grade" },
{ $unwind: "$section" },
{$project:
{
_id:0,
"grade_id":"$grade._id",
"section_id":"$section._id",
maxStudent:1
}
}
])
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