cursor.returnKey()
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Definition
cursor.returnKey( )-
New in version 3.2.
Modifies the cursor to return index keys rather than the documents.
The
cursor.returnKey()has the following form:cursor.returnKey()Returns: The cursor that returnKey()is attached to with a modified result set. This allows for additional cursor modifiers to be chained.
Behavior
If the query does not use an index to perform the read operation, the cursor returns empty documents.
Example
The restaurants collection contains documents with the following schema:
{
"_id" : ObjectId("564f3a35b385149fc7e3fab9"),
"address" : {
"building" : "2780",
"coord" : [
-73.98241999999999,
40.579505
],
"street" : "Stillwell Avenue",
"zipcode" : "11224"
},
"borough" : "Brooklyn",
"cuisine" : "American ",
"grades" : [
{
"date" : ISODate("2014-06-10T00:00:00Z"),
"grade" : "A",
"score" : 5
},
{
"date" : ISODate("2013-06-05T00:00:00Z"),
"grade" : "A",
"score" : 7
}
],
"name" : "Riviera Caterer",
"restaurant_id" : "40356018"
}
The collection has two indexes in addition to the default _id index:
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "guidebook.restaurant"
},
{
"v" : 1,
"key" : {
"cuisine" : 1
},
"name" : "cuisine_1",
"ns" : "guidebook.restaurant"
},
{
"v" : 1,
"key" : {
"_fts" : "text",
"_ftsx" : 1
},
"name" : "name_text",
"ns" : "guidebook.restaurant",
"weights" : {
"name" : 1
},
"default_language" : "english",
"language_override" : "language",
"textIndexVersion" : 3
}
The following code uses the cursor.returnKey() method to return only the indexed fields used for executing the query:
var csr = db.restaurant.find( { "cuisine" : "Japanese" } )
csr.returnKey()
This returns the following:
{ "cuisine" : "Japanese" }
{ "cuisine" : "Japanese" }
{ "cuisine" : "Japanese" }
{ "cuisine" : "Japanese" }
...