Checking if an Index exists in mongodb - mongodb

Question

Is there a command that i can use via javascript in mongo shell that can be used to check if the particular index exists in my mongodb. I am building a script file that would create indexes. I would like that if I run this file multiple number of times then the indexes that already exists are not recreated.
I can use db.collection.getIndexes() to get the collection of all the indexes in my db and then build a logic to ignore the ones that already exists but i was wondering if there is command to get an index and then ignore a script that creates the index. Something like:
If !exists(db.collection.exists("indexname"))
{
create db.collectionName.CreateIndex("IndexName")
}

Answer 1

Creating indexes in MongoDB is an idempotent operation. So running db.names.createIndex({name:1}) would create the index only if it didn't already exist.
The deprecated (as of MongoDB 3.0) alias for createIndex() is ensureIndex() which is a bit clearer on what createIndex() actually does.
Edit:
Thanks to ZitRo for clarifying in comments that calling createIndex() with the same name but different options than an existing index will throw an error MongoError: Index with name: **indexName** already exists with different options as explained in this question.
If you have other reasons for checking, then you can access current index data one of two ways:
As of v3.0, we can use db.names.getIndexes() where names is the name of the collection. Docs here.
Before v3.0, you can access the system.indexes collection and do a find as bri describes below.

Answer 2

Use db.system.indexes and search on it.
If, for example, you have an index called 'indexname', you can search for it like this:
db.system.indexes.find({'name':'indexname'});
If you need to search for that index on a specific collection,then you need to use the ns property (and, it would be helpful to have the db name).
db.system.indexes.find({'name':'indexname', 'ns':'dbname.collection'});
Or, if you absolutely hate including the db name...
db.system.indexes.find({'name':'indexname', 'ns': {$regex:'.collection$'}});
Pulling that together...
So, you're finished check would be:
if(db.system.indexes.find({name:'indexname',ns:{$regex:'.collection$'}}).count()==0) {
db.collection.createIndex({blah:1},{name:'indexname'})
}

Answer 3

Using nodeJS MongoDB driver version 2.2:
const MongoClient = require('mongodb').MongoClient;
exports.dropOldIndexIfExist = dropOldIndexIfExist;
async function dropOldIndexIfExist() {
try {
const mongoConnection = MongoClient.connect('mongodb://localhost:27017/test');
const indexName = 'name_1';
const isIndexExist = await mongoConnection.indexExists(indexName);
if (isIndexExist === true) {
await mongoConnection.dropIndex(indexName);
}
} catch (err) {
console.error('dropOldIndexIfExist', err.message);
throw err;
}
}

Answer 4

I've created a custom method in c# to check if the index exists, using mongo driver:
public bool IndexExists<TDocument>(
IMongoCollection<TDocument> collection, string name)
{
var indexes = collection.Indexes.List().ToList();
var indexNames = indexes
.SelectMany(index => index.Elements)
.Where(element => element.Name == "name")
.Select(name => name.Value.ToString());
return indexNames.Contains(name);
}

Answer 5

maybe we can use something like https://docs.mongodb.com/v3.2/reference/method/db.collection.getIndexes/#db.collection.getIndexes to check if the collection have an index equal to something ?
if yes then drop and add the new one or add the new one directly

Answer 6

In my case i did as follows.
DBCollection yourcollectionName = mt.getCollection("your_collection");
if (yourcollectionName.getIndexInfo() == null || yourcollectionName.getIndexInfo().isEmpty()) {
DBObject indexOptions = new BasicDBObject();
indexOptions.put("pro1", 1);
indexOptions.put("pro2", 1);
yourcollectionName.createIndex(indexOptions, "name_of_your_index", true);
}

Answer 7

Here is a Python 3.5+ and pymongo >= 4.1 (type hints) function that I wrote which checks to see if the index name exists (other details about the index are omitted).
from pymongo import MongoClient
from pymongo.collection import Collection
def check_collection_indexes(db: MongoClient, collection_name: str, index_name: str) -> bool:
coll: Collection = db[collection_name]
indexes: dict = coll.index_information()
# assume false
found = False
# get length of the index name for substring
l = len(index_name)
for k in indexes.keys():
# Substring the keys and check for match
if k[:l] == index_name:
found = True
break
else:
found = False
return found
If the index exists it will return True, otherwise you can use the False output to call another function that creates/recreates the indexes.