Python SQLAlchemy 类型错误 : unhashable type: 'dict' when trying to instantiate model with one-to-many relationship

Question

我正在尝试使用 SQLAlchemy 创建一个包含一对多关系的模型。一份食谱可能有许多与之相关的说明。然而，当我尝试实例化一个菜谱时，我得到TypeError: unhashable type: 'dict'。如果我删除方向参数，一切都会正常，并且它会创建没有任何方向的食谱。我是否遗漏了一些不允许方向参数成为列表的内容？

应用程序.py

data = {
  'cook_time': 15,
  'description': 'Recipe description',
  'directions': [{'order': 1, 'text': 'First direction'},
                 {'order': 2, 'text': 'Second direction'}],
  'image_url': 'https://via.placeholder.com/800x300?text=Recipe+Image',
  'name': 'Test recipe 2',
  'prep_time': 15,
  'servings': 6
}

recipe = models.Recipe(
  name=data['name'],
  description=data['description'],
  image_url=data['image_url'],
  prep_time=data['prep_time'],
  cook_time=data['cook_time'],
  servings=data['servings'],
  directions=data['directions']
)

模型.py

class Recipe(db.Model):
   __tablename__ = 'recipes'

   id = db.Column(db.Integer, primary_key=True)
   name = db.Column(db.String(200), index=True)
   description = db.Column(db.String(2000))
   image_url = db.Column(db.String(200))
   prep_time = db.Column(db.Integer)
   cook_time = db.Column(db.Integer)
   servings = db.Column(db.Integer)

   directions = db.relationship('RecipeDirection', backref='recipes', lazy='dynamic')


class RecipeDirection(db.Model):
   __tablename__ = 'recipe_directions'

   id = db.Column(db.Integer, primary_key=True)
   recipe_id = db.Column(db.Integer, db.ForeignKey('recipes.id'))
   order = db.Column(db.Integer)
   text = db.Column(db.String(1000))

Answer 1

您收到错误是因为 SQLAlchemy 期望方向是 RecipeDirection 列表。要修复此问题，请先创建一个 RecipeDirection 列表。

data = {
  'cook_time': 15,
  'description': 'Recipe description',
  'directions': [{'order': 1, 'text': 'First direction'},
                 {'order': 2, 'text': 'Second direction'}],
  'image_url': 'https://via.placeholder.com/800x300?text=Recipe+Image',
  'name': 'Test recipe 2',
  'prep_time': 15,
  'servings': 6
}

# Create a list of `RecipeDirection`
directions = []
for direction in data.get("directions", []):
    directions.append(models.RecipeDirection(**direction))

recipe = models.Recipe(
  name=data['name'],
  description=data['description'],
  image_url=data['image_url'],
  prep_time=data['prep_time'],
  cook_time=data['cook_time'],
  servings=data['servings'],
  directions=directions  # Now list of RecipieDirection not list of dicts
)

我还建议研究一个序列化程序，它将为您处理编码和序列化嵌套数据结构的一些细节，例如 marshmallow-sqlalchemy