- 
    Type:New Feature 
- 
    Resolution: Duplicate
- 
    Priority:Major - P3 
- 
    None
- 
    Affects Version/s: None
- 
    Component/s: Aggregation Framework
- 
    None
- 
        None
- 
        None
- 
        None
- 
        None
- 
        None
- 
        None
- 
        None
another way to implement cross-collections joins.
ex: 2 collections: Books and Authors.
book = { _id:1, title: 'A', author_id: 1 }
author = { _id: 1, name: 'Me' }
db.aggregate(
 {$collection: 'book', $match: ...},
 {$collection: 'author', $match: ...},
 ...
 {$group: ...},
 {$project: ...}
)
in result (example too):
books_with_authors = [
 {_id:1, title: 'A', author: { _id: 1, name: 'Me' }},
 ...
]
- duplicates
- 
                    SERVER-19095 $lookup -         
- Closed
 
-