Backup table using python

Backing up a table might be useful when you are performing destructive operations. First you can test your changes on a backup and later apply them to the original table.

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Documentation

All required packages are automatically imported by MLJAR Studio for you so you don't have to worry about them.

# import packages
import psycopg
import os
from dotenv import load_dotenv
from psycopg import sql

Make sure you opened a connection in your notebook. To learn how to do it, check out open and test database connection example notebook.

# load credentials from .env file:
load_dotenv(override=True)

# get the credentials
def create_new_connection():
    try:
        conn = psycopg.connect(
            dbname=os.getenv("POSTGRES_DB_NAME"),
            user=os.getenv("POSTGRES_USERNAME"),
            password=os.getenv("POSTGRES_PASSWORD"),
            host=os.getenv("POSTGRES_HOST"),
            port=os.getenv("POSTGRES_PORT"),
        )
        return conn
    # check for errors
    except psycopg.Error as e:
        raise psycopg.Error(f"""
Error occurred while establishing connection: 
    {e}

Maybe you provided wrong credentials, use define new connection recipe to edit them.
Other option is that database server is down or you dont have the right acces to this database.
            """)

# open new connection:
conn = create_new_connection()

Let's list all tables in out database, you can do so using show all tables recipe. In this notebook we will backup the products table.

# if connection was used and closed it is reopen here
if conn.closed:
    conn = create_new_connection()

# run query
with conn:
    with conn.cursor() as cur:

        # query db
        try:
            cur.execute("""
                SELECT table_name
                FROM information_schema.tables
                WHERE table_type = 'BASE TABLE'
                AND table_schema NOT IN ('pg_catalog', 'information_schema');
            """)
        # check for errors
        except psycopg.ProgrammingError as e:
            raise psycopg.ProgrammingError(f"""
Problem running query:
    {e}

Did you spell everything correctly?
You can use show tables and columns recipes.
            """)

        # print the results
        print("Tables:")
        for table in cur.fetchall():
            print(f"{table}")

We will perform the back up using backup table recipe. Provide new table name, and the name of table to backup.

# if connection was used and closed it is reopen here
if conn.closed:
    conn = create_new_connection()

# run query
with conn:
    with conn.cursor() as cur:

        # backup table
        try:
            cur.execute(
							sql.SQL("CREATE TABLE {new} AS TABLE {old}").format(
							  old=sql.Identifier("products"),
							  new=sql.Identifier("products_backup"),
						))
        # check for errors
        except psycopg.ProgrammingError as e:
            raise psycopg.ProgrammingError(f"""
Problem creating table:
    {e}

Are you sure everything is splled correctly and names are unique?
            """)

Listing every table again returns out newly created backuped table.

# if connection was used and closed it is reopen here
if conn.closed:
    conn = create_new_connection()

# run query
with conn:
    with conn.cursor() as cur:

        # query db
        try:
            cur.execute("""
                SELECT table_name
                FROM information_schema.tables
                WHERE table_type = 'BASE TABLE'
                AND table_schema NOT IN ('pg_catalog', 'information_schema');
            """)
        # check for errors
        except psycopg.ProgrammingError as e:
            raise psycopg.ProgrammingError(f"""
Problem running query:
    {e}

Did you spell everything correctly?
You can use show tables and columns recipes.
            """)

        # print the results
        print("Tables:")
        for table in cur.fetchall():
            print(f"{table}")

Conclusions

Backups can prove very useful when you are experimenting and looking for a solution. Just don't forget to do them.

Recipes used in the postgresql-python-backup-table.ipynb

All code recipes used in this notebook are listed below. You can click them to check their documentation.

Packages used in the postgresql-python-backup-table.ipynb

List of packages that need to be installed in your Python environment to run this notebook. Please note that MLJAR Studio automatically installs and imports required modules for you.

psycopg>=3.2.1

python-dotenv>=1.0.1

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