Array operators

The JSON array operators provide methods to manipulate data within an array.

Table 1.
Operator Description Example
$elemMatch Matches array elements in a query. Assume a collection called contacts that contains the following documents:
  • Document 1
    {"name":"Joe",
"friends":[
{"name":"Henry","age":38},
{ "name":"Mary","age":40}
]
}
  • Document 2
    {"name":"John",
"friends":[
{"name":"Del","age":38},
{ "name":"Chris","age":50}
]
}
  • To find all documents with a friend with the name Henry and the age is 38, run the following query:
    db.contacts.find({friends:{$elemMatch:{name:"Henry", age:38}}})
  • Result:
    {"name":"Joe",
"friends":[
{"name":"Henry","age":38},
{ "name":"Mary","age":40}
]
}
$elemMatch Projects array elements in the result of a query.
  • Query:
    Projection: Project elements of friends array that have age as 38.
db.contacts.find({}, {"_id":0, "friends":{"$elemMatch":{"age":38}}})
  • Result:
    {"friends":[{"name":"Henry","age":38}]}
{"friends":[{"name":"Del","age":38}]}