如何在将jsonObject转换为模型对象时检测缺少的字段

import json

class MyModel:
    def __init__(self, data):
        self.field1 = data.get('field1')
        self.field2 = data.get('field2')
        self.field3 = data.get('field3')

def convert_json_to_model(json_str):
    data = json.loads(json_str)
    model = MyModel(data)
    
    # 检测缺少的字段
    missing_fields = []
    if model.field1 is None:
        missing_fields.append('field1')
    if model.field2 is None:
        missing_fields.append('field2')
    if model.field3 is None:
        missing_fields.append('field3')
    
    if missing_fields:
        raise ValueError(f"Missing fields: {', '.join(missing_fields)}")
    
    return model

# 示例用法
json_str = '{"field1": "value1", "field2": "value2"}'
try:
    model = convert_json_to_model(json_str)
    # 执行其他操作
except ValueError as e:
    print(str(e))