[SQLAlchemy实践]对象 JSON 序列化

发表于

通常使用SQLAlchemy返回对应的模型对象，在某些场景下我们需要将SQLAlchemy对象进行JSON序列化

在Python标准库的json包中，提供了JSONEncoder和JSONDecoder两个类来实现Json字符串和dict类型数据的互相转换。

默认支持数据类型：

Supports the following objects and types by default:

+-------------------+---------------+
| Python            | JSON          |
+===================+===============+
| dict              | object        |
+-------------------+---------------+
| list, tuple       | array         |
+-------------------+---------------+
| str               | string        |
+-------------------+---------------+
| int, float        | number        |
+-------------------+---------------+
| True              | true          |
+-------------------+---------------+
| False             | false         |
+-------------------+---------------+
| None              | null          |
+-------------------+---------------+

通过继承JSONEncoder，实现default方法来自定义SQLAlchemy对象转化成JSON字符串

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
from sqlalchemy import inspect
from sqlalchemy.ext.declarative import DeclarativeMeta

class AlchemyEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj.__class__, DeclarativeMeta):
            fields = {}
            for field in [c.key for c in inspect(obj).mapper.column_attrs]:
                data = obj.__getattribute__(field)
                try:
                    if isinstance(data, datetime):
                        data = data.strftime('%Y-%m-%d %H:%M:%S') # 添加对datetime序列化的支持
                    json.dumps(data)  # this will fail on non-encodable values, like other classes
                    fields[field] = data
                except TypeError:
                    fields[field] = None
            return fields

        return json.JSONEncoder.default(self, obj)