如何從數據庫中的樹數據結構創建一個json對象？

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") 

，我想從這個模型在導航菜單使用創建一個JSON對象。

我想遞歸解析它，並建立一個分層的JSON對象，它看起來是這樣的：

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

我使用了一個查詢數據庫，並返回JSON稱爲Flask-Restless庫。它使用SQLAlchemy。

如果你不想集成這樣的東西，你可以繼承你的SQLAlchemy模型，並運行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）