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How to use SQLAlchemy ORM to access AlloyDB Data in Python

Create Python applications and scripts that use SQLAlchemy Object-Relational Mappings of AlloyDB data.

The rich ecosystem of Python modules lets you get to work quickly and integrate your systems effectively. With the CData Python Connector for AlloyDB and the SQLAlchemy toolkit, you can build AlloyDB-connected Python applications and scripts. This article shows how to use SQLAlchemy to connect to AlloyDB data to query, update, delete, and insert AlloyDB data.

With built-in optimized data processing, the CData Python Connector offers unmatched performance for interacting with live AlloyDB data in Python. When you issue complex SQL queries from AlloyDB, the CData Connector pushes supported SQL operations, like filters and aggregations, directly to AlloyDB and utilizes the embedded SQL engine to process unsupported operations client-side (often SQL functions and JOIN operations).

Connecting to AlloyDB Data

Connecting to AlloyDB data looks just like connecting to any relational data source. Create a connection string using the required connection properties. For this article, you will pass the connection string as a parameter to the create_engine function.

The following connection properties are usually required in order to connect to AlloyDB.

Server: The host name or IP of the server hosting the AlloyDB database.
User: The user which will be used to authenticate with the AlloyDB server.
Password: The password which will be used to authenticate with the AlloyDB server.

You can also optionally set the following:

Database: The database to connect to when connecting to the AlloyDB Server. If this is not set, the user's default database will be used.
Port: The port of the server hosting the AlloyDB database. This property is set to 5432 by default.

Authenticating with Standard Authentication

Standard authentication (using the user/password combination supplied earlier) is the default form of authentication.

No further action is required to leverage Standard Authentication to connect.

Authenticating with pg_hba.conf Auth Schemes

There are additional methods of authentication available which must be enabled in the pg_hba.conf file on the AlloyDB server.

Find instructions about authentication setup on the AlloyDB Server here.

Authenticating with MD5 Authentication

This authentication method must be enabled by setting the auth-method in the pg_hba.conf file to md5.

Authenticating with SASL Authentication

This authentication method must be enabled by setting the auth-method in the pg_hba.conf file to scram-sha-256.

Authenticating with Kerberos

The authentication with Kerberos is initiated by AlloyDB Server when the ∏ is trying to connect to it. You should set up Kerberos on the AlloyDB Server to activate this authentication method. Once you have Kerberos authentication set up on the AlloyDB Server, see the Kerberos section of the help documentation for details on how to authenticate with Kerberos.

Follow the procedure below to install SQLAlchemy and start accessing AlloyDB through Python objects.

Install Required Modules

Use the pip utility to install the SQLAlchemy toolkit and SQLAlchemy ORM package:

pip install sqlalchemy
pip install sqlalchemy.orm

Be sure to import the appropriate modules:

from sqlalchemy import create_engine, String, Column
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

Model AlloyDB Data in Python

You can now connect with a connection string. Use the create_engine function to create an Engine for working with AlloyDB data.

NOTE: Users should URL encode the any connection string properties that include special characters. For more information, refer to the SQL Alchemy documentation.


engine = create_engine("alloydb:///?User=alloydb&Password=admin&Database=alloydb&Server=127.0.0.1&Port=5432")

Declare a Mapping Class for AlloyDB Data

After establishing the connection, declare a mapping class for the table you wish to model in the ORM (in this article, we will model the Orders table). Use the sqlalchemy.ext.declarative.declarative_base function and create a new class with some or all of the fields (columns) defined.


base = declarative_base()
class Orders(base):
	__tablename__ = "Orders"
	ShipName = Column(String,primary_key=True)
	ShipCity = Column(String)
	...

Query AlloyDB Data

With the mapping class prepared, you can use a session object to query the data source. After binding the Engine to the session, provide the mapping class to the session query method.

Using the query Method


engine = create_engine("alloydb:///?User=alloydb&Password=admin&Database=alloydb&Server=127.0.0.1&Port=5432")
factory = sessionmaker(bind=engine)
session = factory()
for instance in session.query(Orders).filter_by(ShipCountry="USA"):
	print("ShipName: ", instance.ShipName)
	print("ShipCity: ", instance.ShipCity)
	print("---------")

Alternatively, you can use the execute method with the appropriate table object. The code below works with an active session.

Using the execute Method


Orders_table = Orders.metadata.tables["Orders"]
for instance in session.execute(Orders_table.select().where(Orders_table.c.ShipCountry == "USA")):
	print("ShipName: ", instance.ShipName)
	print("ShipCity: ", instance.ShipCity)
	print("---------")

For examples of more complex querying, including JOINs, aggregations, limits, and more, refer to the Help documentation for the extension.

Insert AlloyDB Data

To insert AlloyDB data, define an instance of the mapped class and add it to the active session. Call the commit function on the session to push all added instances to AlloyDB.


new_rec = Orders(ShipName="placeholder", ShipCountry="USA")
session.add(new_rec)
session.commit()

Update AlloyDB Data

To update AlloyDB data, fetch the desired record(s) with a filter query. Then, modify the values of the fields and call the commit function on the session to push the modified record to AlloyDB.


updated_rec = session.query(Orders).filter_by(SOME_ID_COLUMN="SOME_ID_VALUE").first()
updated_rec.ShipCountry = "USA"
session.commit()

Delete AlloyDB Data

To delete AlloyDB data, fetch the desired record(s) with a filter query. Then delete the record with the active session and call the commit function on the session to perform the delete operation on the provided records (rows).


deleted_rec = session.query(Orders).filter_by(SOME_ID_COLUMN="SOME_ID_VALUE").first()
session.delete(deleted_rec)
session.commit()

Free Trial & More Information

Download a free, 30-day trial of the CData Python Connector for AlloyDB to start building Python apps and scripts with connectivity to AlloyDB data. Reach out to our Support Team if you have any questions.

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