This tutorial shows you how to work with MySQL BLOB data in Python, with examples of updating and reading BLOB data.
The authors table has a column named photo whose data type is BLOB. We will read data from a picture file and update to the photo column.
Updating BLOB data in Python
First, we develop a function named read_file() that reads a file and returns the file’s content:
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def read_file(filename): with open(filename, ‘rb‘) as f: photo = f.read() return photo |
Second, we create a new function named update_blob() that updates photo for an author specified by author_id .
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from mysql.connector import MySQLConnection, Error from python_mysql_dbconfig import read_db_config def update_blob(author_id, filename): # read file data = read_file(filename) # prepare update query and data query = "UPDATE authors " \ "SET photo = %s " \ "WHERE id = %s" args = (data, author_id) db_config = read_db_config() try: conn = MySQLConnection(**db_config) cursor = conn.cursor() cursor.execute(query, args) conn.commit() except Error as e: print(e) finally: cursor.close() conn.close() |
Let’s examine the code in detail:
- First, we call the
read_file()function to read data from a file and return it. - Second, we compose an UPDATE statement that updates photo column for an author specified by
author_id. Theargsvariable is a tuple that contains file data andauthor_id. We will pass this variable to theexecute()method together with thequery. - Third, inside the
try exceptblock, we connect to the database, instantiate a cursor, and execute the query withargs. To make the change effective, we callcommit()method of the MySQLConnection object. - Fourth, we close the cursor and database connection in the
finallyblock.
Notice that we imported MySQLConnection and Error objects from the MySQL Connector/Python package and read_db_config() function from the python_mysql_dbconfig module that we developed in the previous tutorial.
Let’s test the update_blob() function.
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def main(): update_blob(144, "pictures\garth_stein.jpg") if __name__ == ‘__main__‘: main() |
Notice that you can use the following photo and put it into the pictures folder for testing.
Inside the main function, we call the update_blob() function to update the photo column for the author with id 144. To verify the result, we select data from the authors table.
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SELECT * FROM authors WHERE id = 144; |
It works as expected.
Reading BLOB data in Python
In this example, we select BLOB data from the authors table and write it into a file.
First, we develop a write_file() function that write a binary data into a file as follows:
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def write_file(data, filename): with open(filename, ‘wb‘) as f: f.write(data) |
Second, we create a new function named read_blob() as below:
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def read_blob(author_id, filename): # select photo column of a specific author query = "SELECT photo FROM authors WHERE id = %s" # read database configuration db_config = read_db_config() try: # query blob data form the authors table conn = MySQLConnection(**db_config) cursor = conn.cursor() cursor.execute(query, (author_id,)) photo = cursor.fetchone()[0] # write blob data into a file write_file(photo, filename) except Error as e: print(e) finally: cursor.close() conn.close() |
The read_blob() function reads BLOB data from the authors table and write it into a file specified by the filename parameter.
The code is straightforward:
- First, we compose a SELECT statement that retrieves photo of a specific author.
- Second, we get the database configuration by calling the
read_db_config()function. - Third, inside the
try exceptblock, we connect to the database, instantiate cursor, and execute the query. Once we got the BLOB data, we use thewrite_file()function to write it into a file specified by thefilename. - Fourth, in the finally block, we close the cursor and database connection.
Now, let’s test the read_blob() function.
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def main(): read_blob(144,"output\garth_stein.jpg") if __name__ == ‘__main__‘: main() |
If you open the output folder in the project and see a picture there, it means that you have successfully read the blob from the database.