# MongoDB with MongoEngine — Flask Documentation (3.1.x)

# MongoDB with MongoEngine

Using a document database like MongoDB is a common alternative to relational SQL databases. This pattern shows how to use MongoEngine, a document mapper library, to integrate with MongoDB.

A running MongoDB server and Flask-MongoEngine are required.

    pip install flask-mongoengine

## Configuration

Basic setup can be done by defining `MONGODB_SETTINGS` on `app.config` and creating a `MongoEngine` instance.

    from flask import Flask
    from flask_mongoengine import MongoEngine

    app = Flask(__name__)
    app.config['MONGODB_SETTINGS'] = {
        "db": "myapp",
    }
    db = MongoEngine(app)

## Mapping Documents

To declare a model that represents a Mongo document, create a class that inherits from `Document` and declare each of the fields.

    import mongoengine as me

    class Movie(me.Document):
        title = me.StringField(required=True)
        year = me.IntField()
        rated = me.StringField()
        director = me.StringField()
        actors = me.ListField()

If the document has nested fields, use `EmbeddedDocument` to defined the fields of the embedded document and `EmbeddedDocumentField` to declare it on the parent document.

    class Imdb(me.EmbeddedDocument):
        imdb_id = me.StringField()
        rating = me.DecimalField()
        votes = me.IntField()

    class Movie(me.Document):
        ...
        imdb = me.EmbeddedDocumentField(Imdb)

## Creating Data

Instantiate your document class with keyword arguments for the fields. You can also assign values to the field attributes after instantiation. Then call `doc.save()`.

    bttf = Movie(title="Back To The Future", year=1985)
    bttf.actors = [
        "Michael J. Fox",
        "Christopher Lloyd"
    ]
    bttf.imdb = Imdb(imdb_id="tt0088763", rating=8.5)
    bttf.save()

## Queries

Use the class `objects` attribute to make queries. A keyword argument looks for an equal value on the field.

    bttf = Movies.objects(title="Back To The Future").get_or_404()

Query operators may be used by concatenating them with the field name using a double-underscore. `objects`, and queries returned by calling it, are iterable.

    some_theron_movie = Movie.objects(actors__in=["Charlize Theron"]).first()

    for recents in Movie.objects(year__gte=2017):
        print(recents.title)

## Documentation

There are many more ways to define and query documents with MongoEngine. For more information, check out the official documentation.

Flask-MongoEngine adds helpful utilities on top of MongoEngine. Check out their documentation as well.