Mongoengine is a Python Object-Data Mapper (ODM) that provides a high-level abstraction for working with MongoDB databases. It allows developers to interact with MongoDB using Python objects, making it easier to work with data in MongoDB.

One of the great features of Mongoengine is its support for multiple databases. This feature enables developers to work with different databases within the same Python application, providing flexibility and scalability.

Setting up multiple databases

To work with multiple databases using Mongoengine, you need to define a separate connection for each database. Let’s start by installing the required packages:

pip install mongoengine

Now, let’s define two separate connections for different databases:

from mongoengine import connect

# Connection for the first database
connect('db1', host='localhost', port=27017)

# Connection for the second database
connect('db2', host='localhost', port=27017)

In the above example, we have set up connections for two databases: db1 and db2. Make sure to replace 'localhost' and 27017 with the appropriate host and port of your MongoDB server.

Using multiple databases

Once the connections are established, you can define your Mongoengine models and use them with different databases. Here’s how you can define a model for each database:

from mongoengine import Document, StringField

# Model for the first database (db1)
class User1(Document):
    name = StringField()

    meta = {'db_alias': 'db1'}

# Model for the second database (db2)
class User2(Document):
    name = StringField()

    meta = {'db_alias': 'db2'}

In the above example, we have defined two models: User1 and User2, which correspond to the db1 and db2 databases, respectively. The meta attribute with 'db_alias' is used to specify the database alias for each model.

Working with multiple databases

To interact with the models and perform database operations, you need to specify the database alias for each query. Here’s how you can query and save objects in multiple databases:

# Querying objects in db1
users_db1 = User1.objects.using('db1')

# Querying objects in db2
users_db2 = User2.objects.using('db2')

# Saving objects in db1
user1 = User1(name='John Doe').save(using='db1')

# Saving objects in db2
user2 = User2(name='Jane Smith').save(using='db2')

In the above example, we have used the using() method to specify the database alias for each operation. The save() method also accepts the using parameter to specify the database for saving the object.

Conclusion

Mongoengine’s support for multiple databases in Python is a powerful feature for developers working with MongoDB. It allows you to manage different databases within the same application, providing flexibility and scalability. By following the examples and guidelines provided in this blog post, you can easily work with multiple databases using Mongoengine in Python.