Database Reference
In-Depth Information
To confirm that the given index is being used, you can optionally add the
explain()
function, returning
information about the query plan chosen. Here, the
indexBounds
value tells you about the index used:
> db.media.find( { ISBN: " 978-1-4302-5821-6"} ) . hint ( { ISBN: 1 } ).explain()
{
"cursor" : "BtreeCursor ISBN_1",
"isMultiKey" : false,
"n" : 1,
"nscannedObjects" : 1,
"nscanned" : 1,
"nscannedObjectsAllPlans" : 1,
"nscannedAllPlans" : 1,
"scanAndOrder" : false,
"indexOnly" : false,
"nYields" : 0,
"nChunkSkips" : 0,
"millis" : 0,
"indexBounds" : {
"ISBN" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
},
"server" : "localhost:27017"
}
Constraining Query Matches
The
min()
and
max()
functions enable you to constrain query matches to only those that have index keys between the
min and max keys specified. Therefore, you will need to have an index for the keys you are specifying. Also, you can
either combine the two functions or use them separately. Let's begin by adding a few documents that enable you to
take advantage of these functions. First, create an index on the
Released
field:
> db.media.insert( { "Type" : "DVD", "Title" : "Matrix, The", "Released" :
1999} )
> db.media.insert( { "Type" : "DVD", "Title" : "Blade Runner", "Released" :
1982 } )
> db.media.insert( { "Type" : "DVD", "Title" : "Toy Story 3", "Released" :
2010} )
> db.media.ensureIndex( { "Released": 1 } )
