How to save a image file on a Postgres database?

Question

For learning purposes, I'm creating a site using Python+Flask. I want to recover an image from database and show it on screen. But one step at a time.

I have no idea how to save an image in my database in the first place. My searches only revealed that I have to use a bytea type in my database. Then I get my image and somehow (??) convert it to an array of bytes (bytea == array of bites?) and somehow (??) use this array in a insert command.

I was able to discover (maybe) how to do it in Java (here) and C# (here), but I would really like to use Python, at least for now.

Can someone help me?

There are tons of questions of this kind in this site. But most (easily over 85%) of them are replied as "You shouldn't save images in your database, they belong in fs" and fail to answer the question. The rest don't quite solve my problem. So please don't mark this as duplicate if the duplicate has this kind of answer.

Answer 1

I don't normally write complete example programs for people, but you didn't demand it and it's a pretty simple one, so here you go:

#!/usr/bin/env python3

import os
import sys
import psycopg2
import argparse

db_conn_str = "dbname=regress user=craig"

create_table_stm = """
CREATE TABLE files (
    id serial primary key,
    orig_filename text not null,
    file_data bytea not null
)
"""

def main(argv):
    parser = argparse.ArgumentParser()
    parser_action = parser.add_mutually_exclusive_group(required=True)
    parser_action.add_argument("--store", action='store_const', const=True, help="Load an image from the named file and save it in the DB")
    parser_action.add_argument("--fetch", type=int, help="Fetch an image from the DB and store it in the named file, overwriting it if it exists. Takes the database file identifier as an argument.", metavar='42')
    parser.add_argument("filename", help="Name of file to write to / fetch from")

    args = parser.parse_args(argv[1:])

    conn = psycopg2.connect(db_conn_str)
    curs = conn.cursor()

    # Ensure DB structure is present
    curs.execute("SELECT 1 FROM information_schema.tables WHERE table_schema = %s AND table_name = %s", ('public','files'))
    result = curs.fetchall()
    if len(result) == 0:
        curs.execute(create_table_stm)

    # and run the command
    if args.store:
        # Reads the whole file into memory. If you want to avoid that,
        # use large object storage instead of bytea; see the psycopg2
        # and postgresql documentation.
        f = open(args.filename,'rb')

        # The following code works as-is in Python 3.
        #
        # In Python 2, you can't just pass a 'str' directly, as psycopg2
        # will think it's an encoded text string, not raw bytes. You must
        # either use psycopg2.Binary to wrap it, or load the data into a
        # "bytearray" object.
        #
        # so either:
        #
        #   filedata = psycopg2.Binary( f.read() )
        #
        # or
        #
        #   filedata = buffer( f.read() )
        #
        filedata = f.read()
        curs.execute("INSERT INTO files(id, orig_filename, file_data) VALUES (DEFAULT,%s,%s) RETURNING id", (args.filename, filedata))
        returned_id = curs.fetchone()[0]
        f.close()
        conn.commit()
        print("Stored {0} into DB record {1}".format(args.filename, returned_id))

    elif args.fetch is not None:
        # Fetches the file from the DB into memory then writes it out.
        # Same as for store, to avoid that use a large object.
        f = open(args.filename,'wb')
        curs.execute("SELECT file_data, orig_filename FROM files WHERE id = %s", (int(args.fetch),))
        (file_data, orig_filename) = curs.fetchone()

            # In Python 3 this code works as-is.
            # In Python 2, you must get the str from the returned buffer object.
        f.write(file_data)
        f.close()
        print("Fetched {0} into file {1}; original filename was {2}".format(args.fetch, args.filename, orig_filename))

    conn.close()

if __name__ == '__main__':
    main(sys.argv)

Written with Python 3.3. Using Python 2.7 requires that you read the file and convert to a buffer object or use the large object functions. Converting to Python 2.6 and older requires installation of argparse, probably other changes.

You'll want to change the database connection string to something suitable for your system if you're going to test-run it.

If you're working with big images consider using psycopg2's large object support instead of bytea - in particular, lo_import for store, lo_export for writing directly to a file, and the large object read functions for reading small chunks of the image at a time.