pynamodb基于已有类对象创建模型

Question

我正在Python Flask项目中使用pynamodb，并开始构建我的模型来定义将用于表的对象。

文档说明您可以按如下方式定义模型：

from pynamodb.models import Model
from pynamodb.attributes import UnicodeAttribute

    class UserModel(Model):
        """
        A DynamoDB User
        """
        class Meta:
            table_name = "dynamodb-user"
        email = UnicodeAttribute(null=True)
        first_name = UnicodeAttribute(range_key=True)
        last_name = UnicodeAttribute(hash_key=True)

但是，我已经在另一个模块中定义了一个已存在的类，如下所示：

class ActivityTask:
    def __init__(self,task_name, sequence_order):
        self.taskid = uuid.uuid4()
        self.taskcreated = datetime.datetime.now()
        self.taskname = task_name
        self.sequenceorder = sequence_order

有没有办法让我以某种方式“移植”我现有的ActivityTask类对象，以便我可以将其用作模型？因为它已经与所讨论的DynamoDB表的模式匹配。

Answer 1

下面是我创建的一个类，用于从Marshmellow类自动生成Pynamodb模型：

class PynamodbModel:
def __init__(self, base_object):
    self.base_object = base_object

    attributes = self.make_attributes(self.base_object.schema)

    meta_attr = {"table_name" : self.base_object.__name__}

    attributes['Meta'] = type("Meta", (), meta_attr)

    self.table : Model = type("Table", (Model,), attributes)

def convert_attr(self, attr):
    if type(attr) == Nested:
        atttr = attr.inner.nested

def make_attributes(self, schema_obj):
    attributes = {}

    for name, elem in schema_obj._declared_fields.items():
        if name == 'id':
            attributes[name] = attibute_conversion[type(elem)](hash_key=True)
        elif type(elem) == List:
            if type(elem.inner) == Nested:
                attributes[name] = attibute_conversion[type(elem)](of=self.make_nested_attr(elem.inner.nested))
            else:
                attributes[name] = attibute_conversion[type(elem)]()

        elif type(elem) == Nested:
            attributes[name] = self.make_nested_attr(elem.nested)

        else:
            attributes[name] = attibute_conversion[type(elem)]()

    return attributes

def make_nested_attr(self, nested_schema):

    attributes = self.make_attributes(nested_schema)

    return type(nested_schema.__class__.__name__, (MapAttribute,), attributes)

Go here to see the full example !

基本上，我只是迭代Marshmellow Schema属性并分配相应的Pynamodb属性。希望它能帮上忙！