MongoDBis an open-source document-oriented database. MongoDB stores data in the form of key-value pairs and is a NoSQL database program. The term NoSQL means non-relational.

Indexing 

Indexing helps in querying the documents efficiently. Itstores the value of a specific field or set of fields which are ordered by the value of the field as specified in the index. 

PyMongo contains a functioncreate_index()to explicitly create index. By default,_idis the only index present in the collection. This function can accept either a key or a list of (key, direction) pairs.

Syntax: 

create_index(keys, session=None, **kwargs)

Let's look at some examples.

Example 1:

Sample Database:

frompymongoimportMongoClient# creation of MongoClientclient=MongoClient()# Connect with the portnumber and hostclient=MongoClient("mongodb://localhost:27017/")# Access databasemydatabase=client['GFG']# Access collection of the databasemycollection=mydatabase['College']# Before Creating indexindex_list=sorted(list(mycollection.index_information()))print("Before Creating index")print(index_list)# Creating indexmycollection.create_index("student_id",unique=True)# After Creating indexindex_list=sorted(list(mycollection.index_information()))print("\nAfter Creating index")print(index_list)

Output:

Before Creating index['_id_']After Creating index['_id_', 'student_id_1']

1. Here, we create an index namedstudent_idusing create_index() method. This results in two indexes in the documents_idandstudent_id.
2. Usingindex_information() method, we get all the indexes in the collection,

Example 2:

frompymongoimportMongoClient# creation of MongoClientclient=MongoClient()# Connect with the portnumber and hostclient=MongoClient("mongodb://localhost:27017/")# Access databasemydatabase=client['GFG']# Access collection of the databasemycollection=mydatabase['College']record={'_id':4,"student_id":873,"name":"John","section":"A"}mycollection.insert_one(record)

Output:

DuplicateKeyError                         Traceback (most recent call last)<ipython-input-62-264f0e13db93> in<module>     16 record={'_id':4,"student_id":873,"name":"John","section":"A"}     17---> 18mycollection.insert_one(record)

DuplicateKeyError: E11000 duplicate key error collection: GFG.College index: student_id_1 dup key: { : 873 }

It raises theDuplicateKeyError as there is already a document that exists with the student_id 873 and we are trying to insert another document with the same student_id. This error occurs because we created an index on the field student_id and marked it as unique.

Similar Reads