如何从数据库中的树数据结构创建 json 对象？

Question

我正在使用以下型号的烧瓶：

class NewsCategory(db.Model):
    __tablename__ = 'news_category'
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(64))
    parent_id = db.Column(db.Integer, db.ForeignKey('news_category.id'))
    children = db.relationship("NewsCategory")

我想从这个模型中创建一个用于导航菜单的 json 对象。

我想递归解析它并构建一个看起来像这样的分层 JSON 对象：

tree = [{"title": "Node 1", "id": "1"},
         {"title": "Folder 2", "id": "2", "folder": "true", "children": [
            {"title": "Node 2.1", "id": "3"},
            {"title": "Node 2.2", "id": "4"}
          ]}
        ]

Answer 1

我使用一个名为 Flask-Restless 的库来查询数据库并返回 json。它适用于 SQLAlchemy。

如果您不希望与这样的东西集成，您可以将您的 SQLAlchemy 模型子类化并在其上运行 to_json() 方法。

class NewsCategory(db.Model, JsonSerializer)

class JsonSerializer(object):
    """A mixin that can be used to mark a SQLAlchemy model class which
    implements a :func:`to_json` method. The :func:`to_json` method is used
    in conjuction with the custom :class:`JSONEncoder` class. By default this
    mixin will assume all properties of the SQLAlchemy model are to be visible
    in the JSON output. Extend this class to customize which properties are
    public, hidden or modified before being being passed to the JSON serializer.
    """

    __json_public__ = None
    __json_hidden__ = None
    __json_modifiers__ = None

    def get_field_names(self):
        for p in self.__mapper__.iterate_properties:
            yield p.key

    def to_json(self):
        field_names = self.get_field_names()

        public = self.__json_public__ or field_names
        hidden = self.__json_hidden__ or []
        modifiers = self.__json_modifiers__ or dict()

        rv = dict()
        for key in public:
            rv[key] = getattr(self, key)
        for key, modifier in modifiers.items():
            value = getattr(self, key)
            rv[key] = modifier(value, self)
        for key in hidden:
            rv.pop(key, None)
        return rv

来源：Github Overholt project（Flask-Security 的作者）