MongoDB is a cross-platform, document-oriented database that works on the concept of collections and documents. It stores data in the form of key-value pairs and is a NoSQL database program. The term NoSQL means non-relational. Refer to MongoDB and Python for an in-depth introduction to the topic. Now let’s understand the use of distinct() function in PyMongo.
distinct()
PyMongo includes the distinct() function that finds and returns the distinct values for a specified field across a single collection and returns the results in an array.
Syntax : distinct(key, filter = None, session = None, **kwargs)
Parameters :
- key : field name for which the distinct values need to be found.
- filter : (Optional) A query document that specifies the documents from which to retrieve the distinct values.
- session : (Optional) a ClientSession.
Let’s create a sample collection :
# importing the module from pymongo import MongoClient # creating a MongoClient object client = MongoClient() # connecting with the portnumber and host # accessing the database database = client['database'] # access collection of the database mycollection = mydatabase['myTable'] documents = [{"_id": 1, "dept": "A", "item": {"code": "012", "color": "red"}, "sizes": ["S", "L"]}, {"_id": 2, "dept": "A", "item": {"code": "012", "color": "blue"}, "sizes": ["M", "S"]}, {"_id": 3, "dept": "B", "item": {"code": "101", "color": "blue"}, "sizes": "L"}, {"_id": 4, "dept": "A", "item": {"code": "679", "color": "black"}, "sizes": ["M"]}] mycollection.insert_many(documents) for doc in mycollection.find({}): print(doc) |
Output :
{'_id': 1, 'dept': 'A', 'item': {'code': '012', 'color': 'red'}, 'sizes': ['S', 'L']}
{'_id': 2, 'dept': 'A', 'item': {'code': '012', 'color': 'blue'}, 'sizes': ['M', 'S']}
{'_id': 3, 'dept': 'B', 'item': {'code': '101', 'color': 'blue'}, 'sizes': 'L'}
{'_id': 4, 'dept': 'A', 'item': {'code': '679', 'color': 'black'}, 'sizes': ['M']}
Now we will; use the distinct() method to :
- Return distinct values for a Field
- Return Distinct Values for an Embedded Field
- Return Distinct Values for an Array Field
- Return Specific Query
# distinct() function returns the distinct values for the # field dept from all documents in the mycollection collection print(mycollection.distinct('dept')) # distinct values for the field color, # embedded in the field item, from all documents # in the mycollection collection print(mycollection.distinct('item.color')) # returns the distinct values for the field sizes # from all documents in the mycollection collection print(mycollection.distinct("sizes")) # distinct values for the field code, # embedded in the field item, from the documents # in mycollection collection whose dept is equal to B. print(mycollection.distinct("item.code", {"dept" : "B"})) |
Output :
['A', 'B'] ['red', 'blue', 'black'] ['L', 'S', 'M'] ['101']
