如何在 MongoDB 中将子文档展平为根级别? [英] How to flatten a subdocument into root level in MongoDB?
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问题描述
For example, if I have a document like this
{
a: 1,
subdoc: {
b: 2,
c: 3
}
}
How can I convert it into a format like this? (without using project
)
{
a: 1,
b: 2,
c: 3
}
解决方案
You can use MongoDB projection i.e $project
aggregation framework pipeline operators as well. (recommended way). If you don't want to use project
check this link
db.collection.aggregation([{$project{ . . }}]);
Below is the example for your case:
db.collectionName.aggregate
([
{ $project: { a: 1, 'b': '$subdoc.b', 'c': '$subdoc.c'} }
]);
Gives you the output as you expected i.e.
{
"a" : 1,
"b" : 2,
"c" : 3
}
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