如何在Postgres数据库中保存图像文件？

Question

出于学习目的,我正在使用Python + Flask创建一个站点.我想从数据库中恢复图像并在屏幕上显示.但是一步一步.

我不知道如何在我的数据库中保存图像.我的搜索只显示我必须bytea在我的数据库中使用一个类型.然后我得到我的图像,并以某种方式(？)将其转换为字节数组(bytea ==数组的咬？)并以某种方式(？)在插入命令中使用此数组.

我能够发现(也许)如何在Java(这里)和C#(这里)中做到这一点,但我真的想使用Python,至少现在.

有人能帮我吗？

这个网站有很多这类问题.但大多数(很容易超过85%)的回复是"您不应该在数据库中保存图像,它们属于fs"并且无法回答问题.其余的并没有完全解决我的问题.因此,如果副本有这样的答案,请不要将其标记为重复.

Answer 1

我通常不会为人们编写完整的示例程序,但是你没有要求它,这是一个非常简单的程序,所以在这里你去:

#!/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)

用Python 3.3编写.使用Python 2.7要求您读取文件并转换为buffer对象或使用大对象函数.转换为Python 2.6及更早版本需要安装argparse,可能还有其他更改.

如果要进行测试运行,您需要将数据库连接字符串更改为适合您系统的字符串.

如果您正在处理大图像,请考虑使用psycopg2的大对象支持,而不是bytea- 特别是lo_import对于存储,lo_export直接写入文件,以及大对象读取函数,用于一次读取图像的小块.

Answer 2

我希望这对你有用。

import Image
import StringIO
im = Image.open("file_name.jpg") # Getting the Image
fp = StringIO.StringIO()
im.save(fp,"JPEG")
output = fp.getvalue() # The output is 8-bit String.

字符串IO 图像