A Flask extension that provides integration with MongoEngine. For more information on MongoEngine please check out the MongoEngine Documentation.

It handles connection management for your app. You can also use WTForms as model forms for your models.

Installing Flask-MongoEngine

Install with pip:

pip install flask-mongoengine


Basic setup is easy, just fetch the extension:

from flask import Flask
from flask_mongoengine import MongoEngine

app = Flask(__name__)
db = MongoEngine(app)

Or, if you are setting up your database before your app is initialized, as is the case with application factories:

from flask import Flask
from flask_mongoengine import MongoEngine
db = MongoEngine()
app = Flask(__name__)

By default, Flask-MongoEngine assumes that the mongod instance is running on localhost on port 27017, and you wish to connect to the database named test.

If MongoDB is running elsewhere, you should provide the host and port settings in the ‘MONGODB_SETTINGS’ dictionary wih app.config.:

app.config['MONGODB_SETTINGS'] = {
    'db': 'project1',
    'host': '',
    'port': 12345

If the database requires authentication, the username and password arguments should be provided ‘MONGODB_SETTINGS’ dictionary wih app.config.:

app.config['MONGODB_SETTINGS'] = {
    'db': 'project1',

Uri style connections are also supported, just supply the uri as the host in the ‘MONGODB_SETTINGS’ dictionary with app.config. Note that database name from uri has priority over name.

app.config['MONGODB_SETTINGS'] = {
    'db': 'project1',
    'host': 'mongodb://localhost/database_name'

Connection settings may also be provided individually by prefixing the setting with ‘MONGODB_’ in the app.config.:

app.config['MONGODB_DB'] = 'project1'
app.config['MONGODB_HOST'] = ''
app.config['MONGODB_PORT'] = 12345
app.config['MONGODB_USERNAME'] = 'webapp'
app.config['MONGODB_PASSWORD'] = 'pwd123'

Custom Queryset

flask-mongoengine attaches the following methods to Mongoengine’s default QuerySet:

  • get_or_404: works like .get(), but calls abort(404) if the object DoesNotExist.
  • first_or_404: same as above, except for .first().
  • paginate: paginates the QuerySet. Takes two arguments, page and per_page.
  • paginate_field: paginates a field from one document in the QuerySet. Arguments: field_name, doc_id, page, per_page.


# 404 if object doesn't exist
def view_todo(todo_id):
    todo = Todo.objects.get_or_404(_id=todo_id)

# Paginate through todo
def view_todos(page=1):
    paginated_todos = Todo.objects.paginate(page=page, per_page=10)

# Paginate through tags of todo
def view_todo_tags(todo_id, page=1):
    todo = Todo.objects.get_or_404(_id=todo_id)
    paginated_tags = todo.paginate_field('tags', page, per_page=10)

Properties of the pagination object include: iter_pages, next, prev, has_next, has_prev, next_num, prev_num.

In the template:

{% macro render_pagination(pagination, endpoint) %}
  <div class=pagination>
  {%- for page in pagination.iter_pages() %}
    {% if page %}
      {% if page != pagination.page %}
        <a href="{{ url_for(endpoint, page=page) }}">{{ page }}</a>
      {% else %}
        <strong>{{ page }}</strong>
      {% endif %}
    {% else %}
      <span class=ellipsis>…</span>
    {% endif %}
  {%- endfor %}
{% endmacro %}

MongoEngine and WTForms

flask-mongoengine automatically generates WTForms from MongoEngine models:

from flask_mongoengine.wtf import model_form

class User(db.Document):
    email = db.StringField(required=True)
    first_name = db.StringField(max_length=50)
    last_name = db.StringField(max_length=50)

class Content(db.EmbeddedDocument):
    text = db.StringField()
    lang = db.StringField(max_length=3)

class Post(db.Document):
    title = db.StringField(max_length=120, required=True, validators=[validators.InputRequired(message=u'Missing title.'),])
    author = db.ReferenceField(User)
    tags = db.ListField(db.StringField(max_length=30))
    content = db.EmbeddedDocumentField(Content)

PostForm = model_form(Post)

def add_post(request):
    form = PostForm(request.POST)
    if request.method == 'POST' and form.validate():
        # do something
    return render_template('add_post.html', form=form)

For each MongoEngine field, the most appropriate WTForm field is used. Parameters allow the user to provide hints if the conversion is not implicit:

PostForm = model_form(Post, field_args={'title': {'textarea': True}})

Supported parameters:

For fields with choices:

  • multiple to use a SelectMultipleField
  • radio to use a RadioField

For StringField:

  • password to use a PasswordField
  • textarea to use a TextAreaField

(By default, a StringField is converted into a TextAreaField if and only if it has no max_length.)

Supported fields

  • StringField
  • BinaryField
  • URLField
  • EmailField
  • IntField
  • FloatField
  • DecimalField
  • BooleanField
  • DateTimeField
  • ListField (using wtforms.fields.FieldList )
  • SortedListField (duplicate ListField)
  • EmbeddedDocumentField (using wtforms.fields.FormField and generating inline Form)
  • ReferenceField (using wtforms.fields.SelectFieldBase with options loaded from QuerySet or Document)
  • DictField

Not currently supported field types:

  • ObjectIdField
  • GeoLocationField
  • GenericReferenceField

Session Interface

To use MongoEngine as your session store simple configure the session interface:

from flask_mongoengine import MongoEngine, MongoEngineSessionInterface

app = Flask(__name__)
db = MongoEngine(app)
app.session_interface = MongoEngineSessionInterface(db)

Debug Toolbar Panel


If you use the Flask-DebugToolbar you can add ‘flask_mongoengine.panels.MongoDebugPanel’ to the DEBUG_TB_PANELS config list and then it will automatically track your queries:

from flask import Flask
from flask_debugtoolbar import DebugToolbarExtension

app = Flask(__name__)
app.config['DEBUG_TB_PANELS'] = ['flask_mongoengine.panels.MongoDebugPanel']
db = MongoEngine(app)
toolbar = DebugToolbarExtension(app)


0.6 to 0.7

ListFieldPagination order of arguments have been changed to be more logical:

# Old order
ListFieldPagination(self, queryset, field_name, doc_id, page, per_page, total)

# New order
ListFieldPagination(self, queryset, doc_id, field_name, page, per_page, total)


Inspired by two repos:

danjac maratfm