Create and drop index in MongoDB 2016-06-12 03:53
Using db.collection.createIndex(keys, options) to create index for a field. If you want create an ascending index on a filed you need specify a value of 1; for descending index use -1. Examples are here.
> db.user.createIndex({name:1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.user.createIndex({age:-1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 2,
"numIndexesAfter" : 3,
"ok" : 1
}
We create two indexes in user collection. When we query document with condition the index will improve query efficiency. You can drop index by using db.collection.dropIndex(index). Examples are here. If you don't know the index name you can use db.collection.getIndexes() to query all indexes in this collection.
> db.user.getIndexes()
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "user_database.user"
},
{
"v" : 1,
"key" : {
"name" : 1
},
"name" : "name_1",
"ns" : "user_database.user"
},
{
"v" : 1,
"key" : {
"age" : -1
},
"name" : "age_-1",
"ns" : "user_database.user"
}
]
> db.user.dropIndex("name_1")
{ "nIndexesWas" : 3, "ok" : 1 }
> db.user.dropIndex("age_-1")
{ "nIndexesWas" : 2, "ok" : 1 }
> db.user.getIndexes()
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "user_database.user"
}
]