如何从数据库中的树数据结构创建一个json对象？

Question

我使用量瓶中，用以下模型：

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") 

，我想从这个模型在导航菜单使用创建一个JSON对象。

我想递归解析它，并建立一个分层的JSON对象，它看起来是这样的：

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

我使用了一个查询数据库，并返回JSON称为Flask-Restless库。它使用SQLAlchemy。

如果你不想集成这样的东西，你可以继承你的SQLAlchemy模型，并运行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 

信用：Github Overholt project（瓶，安全的作者）