{"id":517,"date":"2018-04-20T20:07:02","date_gmt":"2018-04-20T12:07:02","guid":{"rendered":"https:\/\/www.techcoil.com\/blog\/?p=517"},"modified":"2018-04-20T14:37:31","modified_gmt":"2018-04-20T06:37:31","slug":"how-to-paginate-mongoengine-records-in-your-python-3-flask-application","status":"publish","type":"post","link":"https:\/\/www.techcoil.com\/blog\/how-to-paginate-mongoengine-records-in-your-python-3-flask-application\/","title":{"rendered":"How to paginate MongoEngine records in your Python 3 Flask application"},"content":{"rendered":"

Flask<\/a> and MongoEngine<\/a> help makes development work easier. <\/p>\n

One common task in the development of backend applications is the pagination of database records. Without pagination, the application server can run out of memory while generating a response from the database records.<\/p>\n

This post discusses a way to paginate MongoEngine records in your Python 3 Flask application using the facilities provided by the Flask-MongoEngine<\/a> extension.<\/p>\n

Installing flask-mongoengine to your Python 3 environment<\/h2>\n
\r\npip install flask-mongoengine\r\n<\/pre>\n
Associating an instance of flask_mongoengine.MongoEngine<\/code> with an instance of Flask<\/code><\/h2>\n
Once our Python 3 environment had included flask-mongoengine, we can proceed to associate an instance of flask_mongoengine.MongoEngine<\/code> with an instance of Flask<\/code> in our Python 3 script.<\/p>\n
To do so, we can use either the following set of codes:<\/p>\n
\r\nfrom flask import Flask\r\nfrom flask_mongoengine import MongoEngine\r\n\r\napp = Flask(__name__)\r\napp.config.from_pyfile('the-config.cfg')\r\ndb = MongoEngine(app)\r\n<\/pre>\n
or the following set of codes:<\/p>\n
\r\nfrom flask import Flask\r\nfrom flask_mongoengine import MongoEngine\r\n\r\napp = Flask(__name__)\r\napp.config.from_pyfile('the-config.cfg')\r\ndb = MongoEngine()\r\n# Init app later\r\ndb.init_app(app)\r\n<\/pre>\n
Defining a subclass of flask_mongoengine.Document<\/code> to represent our MongoDB collection<\/h2>\n
The next set of codes that we need to write is the definition of a subclass of flask_mongoengine.Document<\/code> that will represent our MongoDB collection:<\/p>\n
\r\n# Note: the db variable refers to the flask_mongoengine.MongoEngine \r\n# instance that we had created earlier.\r\nclass Friend(db.Document):\r\n    \r\n    name = db.StringField(max_length=50, required=True)\r\n    phone_number = db.StringField(max_length=50, required=True)\r\n    \r\n<\/pre>\n
Note that we had used the db<\/code> variable that we can created earlier to get a reference to the flask_mongoengine.Document<\/code> class. We had also defined the fields that we expect the documents in our MongoDB collection to have.<\/p>\n
Calling the paginate function from flask_mongoengine.BaseQuerySet<\/code><\/h2>\n
Once we had defined a subclass of flask_mongoengine.Document<\/code>, we can then use the following codes to query our MongoDB collection and get a paginated record of the result:<\/p>\n
\r\nfriends_pagination = Friend.objects.paginate(page=1, per_page=10)\r\n# Get information of current pagination session\r\ncurrent_page = friends_pagination.page\r\ntotal_pages_for_query = friends_pagination.pages\r\nitem_per_page = friends_pagination.per_page\r\ntotal_number_of_items_that_match_query = friends_pagination.total\r\nlist_of_items = friends_pagination.items\r\n<\/pre>\n
We first define the page number and items per page via the page<\/code> and per_page<\/code> input parameters of the flask_mongoengine.BaseQuerySet.paginate<\/code> function. The execution of this function will return an instance of flask_mongoengine.pagination.Pagination<\/code> class that represents a particular page of a MongoDB query that we had indicated.<\/p>\n
We can then use the instance of flask_mongoengine.pagination.Pagination<\/code> to retrieve:<\/p>\n