django “如何”系列5：如何编写自定义存储系统

﹏ヽ暗。殇╰゛Y 2023-06-04 05:51 5阅读 0赞

如果你需要提供一个自定义的文件存储-一个常见的例子便是在远程系统上存储文件-你可以通过定义一个自己的存储类来做这件事情，你将通过一下步骤：

*  你自定义的存储系统一定是django.core.files.storage.Storage的子类

from django.core.files.storage import Storage
    
    class MyStorage(Storage):
        ...

*  django必须可以实例化你的存储系统（不使用任何参数），这意味着任何的设置都必须从django.conf.settings中拿

from django.conf import settings
    from django.core.files.storage import Storage
    
    class MyStorage(Storage):
        def __init__(self, option=None):
            if not option:
                option = settings.CUSTOM_STORAGE_OPTIONS

*  你的存储类必须实现\_open()和\_save()方法，以及其他的和你存储类相关的方法，下面会讲到
 *  另外，如果你的类提供本地文件存储，你必须覆盖path()方法，如果不，可以忽略这个方法

这是基类Storage的源码，我会在源码的注释中讲解一些内容一些要注意的内容

class Storage(object):
        """    存储基类，提供一些默认的行为供其他的存储系统继承或者覆盖（如果需要的话）    """
        # 下面的方法代表了私有方法的一个公共接口，除非绝对的需要，这些方法不应该被子类覆盖
        def open(self, name, mode='rb'):
            """        从存储中检索特定的文件        """
            return self._open(name, mode)
    
        def save(self, name, content):
            """        用给定的文件名保存给定的新内容，内容应该是一个合适的可以从头开始读取的File对象        """
            # Get the proper name for the file, as it will actually be saved.
            if name is None:
                name = content.name
    
            name = self.get_available_name(name)
            name = self._save(name, content)
    
            # Store filenames with forward slashes, even on Windows
            return force_unicode(name.replace('\\', '/'))
    
        # 这些方法是一部分的公共API（已经实现好的，当然，你可以覆盖）
    
        def get_valid_name(self, name):
            """        Returns a filename, based on the provided filename, that's suitable for
            use in the target storage system.        """
            return get_valid_filename(name)
    
        def get_available_name(self, name):
            """        Returns a filename that's free on the target storage system, and
            available for new content to be written to.        """
            dir_name, file_name = os.path.split(name)
            file_root, file_ext = os.path.splitext(file_name)
            # If the filename already exists, add an underscore and a number (before
            # the file extension, if one exists) to the filename until the generated
            # filename doesn't exist.
            count = itertools.count(1)
            while self.exists(name):
                # file_ext includes the dot.
                name = os.path.join(dir_name, "%s_%s%s" % (file_root, count.next(), file_ext))
    
            return name
    
        def path(self, name):
            """
            Returns a local filesystem path where the file can be retrieved using
            Python's built-in open() function. Storage systems that can't be
            accessed using open() should *not* implement this method.
            """
            raise NotImplementedError("This backend doesn't support absolute paths.")
    
        # 下面的这些方法是没有提供默认实现的公共API，子类一定要实现这些方法
    
        def delete(self, name):
            """        Deletes the specified file from the storage system.        """
            raise NotImplementedError()
    
        def exists(self, name):
            """        Returns True if a file referened by the given name already exists in the
            storage system, or False if the name is available for a new file.        """
            raise NotImplementedError()
    
        def listdir(self, path):
            """        Lists the contents of the specified path, returning a 2-tuple of lists;
            the first item being directories, the second item being files.        """
            raise NotImplementedError()
    
        def size(self, name):
            """        Returns the total size, in bytes, of the file specified by name.        """
            raise NotImplementedError()
    
        def url(self, name):
            """        Returns an absolute URL where the file's contents can be accessed
            directly by a Web browser.        """
            raise NotImplementedError()
    
        def accessed_time(self, name):
            """        Returns the last accessed time (as datetime object) of the file
            specified by name.        """
            raise NotImplementedError()
    
        def created_time(self, name):
            """        Returns the creation time (as datetime object) of the file
            specified by name.        """
            raise NotImplementedError()
    
        def modified_time(self, name):
            """        Returns the last modified time (as datetime object) of the file
            specified by name.        """
            raise NotImplementedError()

看完这个源码，相信你已经知道该如何如写一个自己的存储系统类了（那些方法一定要有的，那些是可以直接用的，那些是一定要写的），下面我们看一下django自带的一个实现吧

class FileSystemStorage(Storage):
        """    Standard filesystem storage    """
        def __init__(self, location=None, base_url=None):
            if location is None:
                location = settings.MEDIA_ROOT
            self.base_location = location
            self.location = abspathu(self.base_location)
            if base_url is None:
                base_url = settings.MEDIA_URL
            self.base_url = base_url
    
        def _open(self, name, mode='rb'):
            return File(open(self.path(name), mode))
    
        def _save(self, name, content):
            full_path = self.path(name)
    
            # Create any intermediate directories that do not exist.
            # Note that there is a race between os.path.exists and os.makedirs:
            # if os.makedirs fails with EEXIST, the directory was created
            # concurrently, and we can continue normally. Refs #16082.
            directory = os.path.dirname(full_path)
            if not os.path.exists(directory):
                try:
                    os.makedirs(directory)
                except OSError, e:
                    if e.errno != errno.EEXIST:
                        raise
            if not os.path.isdir(directory):
                raise IOError("%s exists and is not a directory." % directory)
    
            # There's a potential race condition between get_available_name and
            # saving the file; it's possible that two threads might return the
            # same name, at which point all sorts of fun happens. So we need to
            # try to create the file, but if it already exists we have to go back
            # to get_available_name() and try again.
    
            while True:
                try:
                    # This file has a file path that we can move.
                    if hasattr(content, 'temporary_file_path'):
                        file_move_safe(content.temporary_file_path(), full_path)
                        content.close()
    
                    # This is a normal uploadedfile that we can stream.
                    else:
                        # This fun binary flag incantation makes os.open throw an
                        # OSError if the file already exists before we open it.
                        fd = os.open(full_path, os.O_WRONLY | os.O_CREAT | os.O_EXCL | getattr(os, 'O_BINARY', 0))
                        try:
                            locks.lock(fd, locks.LOCK_EX)
                            for chunk in content.chunks():
                                os.write(fd, chunk)
                        finally:
                            locks.unlock(fd)
                            os.close(fd)
                except OSError, e:
                    if e.errno == errno.EEXIST:
                        # Ooops, the file exists. We need a new file name.
                        name = self.get_available_name(name)
                        full_path = self.path(name)
                    else:
                        raise
                else:
                    # OK, the file save worked. Break out of the loop.
                    break
    
            if settings.FILE_UPLOAD_PERMISSIONS is not None:
                os.chmod(full_path, settings.FILE_UPLOAD_PERMISSIONS)
    
            return name
    
        def delete(self, name):
            name = self.path(name)
            # If the file exists, delete it from the filesystem.
            # Note that there is a race between os.path.exists and os.remove:
            # if os.remove fails with ENOENT, the file was removed
            # concurrently, and we can continue normally.
            if os.path.exists(name):
                try:
                    os.remove(name)
                except OSError, e:
                    if e.errno != errno.ENOENT:
                        raise
    
        def exists(self, name):
            return os.path.exists(self.path(name))
    
        def listdir(self, path):
            path = self.path(path)
            directories, files = [], []
            for entry in os.listdir(path):
                if os.path.isdir(os.path.join(path, entry)):
                    directories.append(entry)
                else:
                    files.append(entry)
            return directories, files
    
        def path(self, name):
            try:
                path = safe_join(self.location, name)
            except ValueError:
                raise SuspiciousOperation("Attempted access to '%s' denied." % name)
            return os.path.normpath(path)
    
        def size(self, name):
            return os.path.getsize(self.path(name))
    
        def url(self, name):
            if self.base_url is None:
                raise ValueError("This file is not accessible via a URL.")
            return urlparse.urljoin(self.base_url, filepath_to_uri(name))
    
        def accessed_time(self, name):
            return datetime.fromtimestamp(os.path.getatime(self.path(name)))
    
        def created_time(self, name):
            return datetime.fromtimestamp(os.path.getctime(self.path(name)))
    
        def modified_time(self, name):
            return datetime.fromtimestamp(os.path.getmtime(self.path(name)))

转载于:https://www.cnblogs.com/qwj-sysu/p/4252126.html