Connect to OceanBase Database by using SQLAlchemy

This topic describes how to connect to OceanBase Database by using SQLAlchemy, and how to perform basic database operations such as creating tables, inserting data, updating data, and querying data.

Prerequisites

• You have installed Python 3.x and pip.
• You have installed OceanBase Database and created a MySQL tenant.

Procedure

1. Obtain the connection string of OceanBase Database.
2. Install the SQLAlchemy library.
3. Write a test.py file and enter the database connection information.
4. Run the test.py file.

Step 1: Obtain the connection string of OceanBase Database

Obtain the database connection string from the deployment personnel or administrator of OceanBase Database.

obclient -h$host -P$port -u$user_name -p$password -D$database_name

Parameters:

• $host: the IP address for connecting to OceanBase Database. For connection through OceanBase Database Proxy (ODP), use the IP address of an ODP. For direct connection, use the IP address of an OBServer node.

• $port: the port for connecting to OceanBase Database. For connection through ODP, the default value is 2883, which can be customized when ODP is deployed. For direct connection, the default value is 2881, which can be customized when OceanBase Database is deployed.

• $database_name: the name of the database to be accessed.

  Notice

  The user used to connect to the tenant must have the CREATE, INSERT, UPDATE, and SELECT privileges on the database. For more information about user privileges, see Privilege types in MySQL mode.

• $user_name: the tenant connection account. For connection through ODP, the format is username@tenant name#cluster name or cluster name:tenant name:username. For direct connection, the format is username@tenant name.

• $password: the password of the account.

For more information about the connection string, see Connect to an OceanBase tenant by using OBClient.

Here is an example:

obclient -hxxx.xxx.xxx.xxx -P2881 -utest_user001@mysql001 -p****** -Dtest

Step 2: Install the SQLAlchemy library

SQLAlchemy is one of the most popular Object Relational Mapping (ORM) libraries in Python. It provides SQL tools and an ORM system to simplify database operations. SQLAlchemy supports multiple database backends, including MySQL, PostgreSQL, and SQLite.

Open the command prompt or PowerShell terminal, and run the following command to install the SQLAlchemy library.

pip install sqlalchemy mysqlclient

After the installation is completed, run the following command to check whether the installation was successful:

pip list | grep SQLAlchemy

Step 3: Write the test.py file and enter the database connection information

Write the test.py file based on the information obtained in Step 1: Obtain the connection string of OceanBase Database and enter the database connection information.

1. Create a file named test.py.

2. Enter the following content into the test.py file and modify the database connection information as needed.

   Here is a sample content of the test.py file:

   from sqlalchemy import create_engine, Column, Integer, String, MetaData, Table
   from sqlalchemy.ext.declarative import declarative_base
   from sqlalchemy.orm import sessionmaker
   
   # Database connection information
   DB_USER = 'test_user001@mysql001'
   DB_PASSWORD = '******'
   DB_HOST = 'xxx.xxx.xxx.xxx'
   DB_PORT = 2881
   DB_NAME = 'test'
   
   # Create a database connection URL
   DATABASE_URL = f"mysql+mysqldb://{DB_USER}:{DB_PASSWORD}@{DB_HOST}:{DB_PORT}/{DB_NAME}"
   
   # Create an engine
   engine = create_engine(DATABASE_URL)
   
   # Create a base class
   Base = declarative_base()
   
   # Define a model
   class User(Base):
       __tablename__ = 'users'
   
       id = Column(Integer, primary_key=True)
       name = Column(String(50), nullable=False)
       age = Column(Integer)
   
       def __repr__(self):
           return f"<User(id={self.id}, name='{self.name}', age={self.age})>"
   
   # Create tables
   Base.metadata.create_all(engine)
   
   # Create a session
   Session = sessionmaker(bind=engine)
   session = Session()
   
   # Insert data
   new_users = [
       User(name='John', age=20),
       User(name='Lucy', age=25),
       User(name='Tom', age=30)
   ]
   session.add_all(new_users)
   session.commit()
   
   # Update data
   user = session.query(User).filter_by(name='Lucy').first()
   if user:
       user.age = 26
       session.commit()
   
   # Query data
   users = session.query(User).all()
   for user in users:
       print(user)
   
   # Close the session
   session.close()
   

Step 4: Run the test.py file

Open the command prompt or PowerShell terminal, run the test.py file, query data, and output the result.

1. Go to the directory where the test.py file is located.

   Here is an example:

   cd D:\demo\demo
   

2. Run the test.py file.

   Here is an example:

   python test.py
   

   The return result is as follows:

   <User(id=1, name='John', age=20)>
   <User(id=2, name='Lucy', age=26)>
   <User(id=3, name='Tom', age=30)>
   

Error handling

When you use SQLAlchemy to connect to OceanBase Database, various errors may occur. The following table describes some common errors and their solutions.

1. Connection error: If you cannot connect to the database, check whether the connection parameters, including the host name, port, username, password, and database name, are correct.

2. Privilege error: If you encounter a privilege error, make sure that the user has sufficient privileges to perform the required operation.

3. SQL syntax error: If there is a syntax error in your SQL statement, check whether the syntax is correct.

4. Data type error: If the data type of the inserted data does not match that defined in the table, make sure that the data type is correct.

In your code, you can use the try-except statement to capture and handle these errors, ensuring that the program can handle errors gracefully instead of crashing. You can also use the logging module to record error information for debugging and troubleshooting.

References

• For more information about how to connect to OceanBase Database, see Overview of connection methods.

• For more information about how to create a database, see CREATE DATABASE.