通过函数调用访问ZODB对象时如何防止ZODB FileStorage出现LockError（单进程）

Question

我在使用 ZODB LockError 时遇到问题，但我相信我只使用单个进程在数据库上运行。

我的项目的目标是只有两个函数，load_project() 和 save_project()，它们允许用户加载 Project 对象，对其进行处理，然后使用 save_project() 间歇性保存它，而无需用户直接与 ZODB 交互。有点像他们只是在处理文档并随时保存。

但是，我注意到我一直收到LockError：我可以加载对象，保存一次对象，但随后每当我尝试保存它时都会收到LockError。显然，关于 ZODB 的工作原理，我做错了或不理解某些事情。 如何防止LockError？

SO 上的所有其他 LockError 问题似乎都涉及多个进程。我通过 Jupyter Notebook 与代码交互，我相信这只是一个过程。当我遇到 LockError 时，我可以重新启动内核（从而启动一个新进程），加载项目然后再次保存。 但是，我无法保存第二次。

这是我从functions 模块导入的两个函数的代码：

def save_project(project: BIMProject):
    """
    Commits the project to the ZODB; including opening and closing the connection
    """
    if not hasattr(project, "filename"):
        project.filename = input("Enter a filename (without extension):")
    if not hasattr(project, "filepath"):
        tk_root = Tk()
        tk_root.withdraw()
        project.filepath = filedialog.askdirectory(title="Please select a directory")

    filename = project.filename
    full_path = project.filepath + "/" + filename

    storage=FileStorage(full_path)
    db=ZODB.DB(storage)
    connection=db.open()
    root=connection.root()
    if 'project' in root:
        root.update({'project': project})
    else:
        root['project'] = project # reassign to change
    transaction.commit()
    connection.close()

def load_project():
    """
    Loads a project from a database file
    """
    tk_root = Tk()
    tk_root.withdraw()
    filepath = filedialog.askopenfilename(title="Please select a database file")

    storage = FileStorage(filepath)
    db = ZODB.DB(storage)
    connection = db.open()
    root = connection.root()
    project = copy.deepcopy(root["project"])
    connection.close()
    db.close()
    return project

任何帮助将不胜感激。

Answer 1

所以，在碰壁一天后，我走了一圈，并决定与其单独通过函数访问数据库，不如使用对象更适合维护与文件存储和数据库的连接。与我想象的不太一样，但效果很好。

class LoaderSaver:
    """
    A 'hang around' object to use in conjunction with Project objects to save them
    in a ZODB FileStorage. Carries the ZODB storage, db, and connection objects once 
    they are opened.

    Only one Project file can be open at one time.
    """
    def __init__(self):
        self.storage = None
        self.db = None
        self.connection = None
        self.root = None

    def load(self):
        """
        Returns a Project object stored in a ZODB file storage. File selected by 
        user in a graphical 'file dialog' interface.
        """
        tk_root = Tk()
        tk_root.withdraw()
        filepath = filedialog.askopenfilename(title="Please select a database file")

        self.storage = FileStorage(filepath)
        self.db = ZODB.DB(self.storage)
        self.connection = self.db.open()
        self.root = self.connection.root()
        project = copy.deepcopy(self.root["project"])
        self.connection.close()
        return project

    def save(self, project: Project):
        """
        Commits the project to the ZODB
        """
        if not hasattr(project, "filename"):
            project.filename = input("Enter a filename (without extension):")
        if not hasattr(project, "filepath"):
            tk_root = Tk()
            tk_root.withdraw()
            project.filepath = filedialog.askdirectory(title="Please select a directory")

        filename = project.filename
        full_path = project.filepath + "/" + filename

        if not (self.storage and self.db):
            self.storage=FileStorage(full_path)
            self.db=ZODB.DB(self.storage)
        else:
            self.connection=self.db.open()
            self.root=self.connection.root()

        self.root['project'] = project
        transaction.commit()
        self.connection.close()