mongodbHow to do joins in MongoDB?
MongoDB supports various types of joins to combine documents from multiple collections. The most commonly used join is the $lookup
operator. It performs a left outer join to an unsharded collection in the same database to filter in documents from the “joined” collection for processing.
db.collection.aggregate([
{
$lookup:
{
from: "otherCollection",
localField: "field1",
foreignField: "field2",
as: "alias_name"
}
}
])
The above example code performs a $lookup
operation on the collection
collection, joining documents from the otherCollection
collection. The localField
and foreignField
parameters specify the fields used to match documents from the two collections. The as
parameter specifies the name of the new array field in the input documents.
Other join operations supported by MongoDB include $merge
, $graphLookup
, $facet
, and $unwind
.
Helpful links
More of Mongodb
- How to use watch in MongoDB?
- How to use unwind in MongoDB?
- How to check the version of MongoDB?
- How to list MongoDB users?
- How to use MongoDB HTTP interface?
- How to use hint in MongoDB?
- How to use triggers in MongoDB?
- How to bind IP addresses for MongoDB server?
- How to rename a field in MongoDB?
- How to work with time series data in MongoDB?
See more codes...