【7.6】通过元类实现简单的orm

  1 #!/user/bin/env python
  2 # -*- coding:utf-8 -*-
  3 # 需求
  4 import numbers
  5 
  6 
  7 class Field:
  8     pass
  9 
 10 
 11 class IntField(Field):
 12     def __init__(self, db_column, min_value=None, max_value=None):
 13         self._value = None
 14         self.db_column = db_column
 15         self.min_value = min_value
 16         self.max_value = max_value
 17         if min_value is not None:
 18             if not isinstance(min_value, numbers.Integral):
 19                 raise ValueError('min_value must be int')
 20             elif min_value < 0:
 21                 raise ValueError('min_value must be positive int')
 22         if max_value is not None:
 23             if not isinstance(max_value, numbers.Integral):
 24                 raise ValueError('max_value must be int')
 25             elif min_value < 0:
 26                 raise ValueError('max_value must be positive int')
 27         if min_value is not None and max_value is not None:
 28             if min_value > max_value:
 29                 raise ValueError('min_value must be smaller than max_value')
 30 
 31     def __get__(self, instance, owner):
 32         return self._value
 33 
 34     def __set__(self, instance, value):
 35         if not isinstance(value, numbers.Integral):
 36             raise ValueError('int value need')
 37         if value < self.min_value or value > self.max_value:
 38             raise ValueError('value must between min_value and max_value')
 39         self._value = value
 40 
 41 
 42 class CharField(Field):
 43     def __init__(self, db_column, max_length=None):
 44         self._value = None
 45         self.db_column = db_column
 46         if max_length is None:
 47             raise ValueError('you must spcify max_length for CharField')
 48         self.max_length = max_length
 49 
 50     def __get__(self, instance, owner):
 51         return self._value
 52 
 53     def __set__(self, instance, value):
 54         if not isinstance(value, str):
 55             raise ValueError('string value need')
 56 
 57         if len(value) > self.max_length:
 58             raise ValueError('value len excess len of max_length')
 59         self._value = value
 60 
 61 
 62 class ModelMetaClass(type):
 63     def __new__(cls, name, bases, attrs, **kwargs):
 64         if name == 'BaseModel':
 65             return super().__new__(cls, name, bases, attrs, **kwargs)
 66         fields = {}
 67         for key, value in attrs.items():
 68             if isinstance(value, Field):
 69                 fields[key] = value
 70         attrs_meta = attrs.get('Meta', None)
 71         _meta = {}
 72         db_table = name.lower()
 73         if attrs_meta is not None:
 74             table = getattr(attrs_meta, 'db_table', None)
 75             if table is None:
 76                 db_table = table
 77         _meta['db_table'] = db_table
 78         attrs['_meta'] = _meta
 79         attrs['fields'] = fields
 80         del attrs['Meta']
 81         return super().__new__(cls, name, bases, attrs, **kwargs)
 82 
 83 
 84 class BaseModel(metaclass=ModelMetaClass):
 85     def __init__(self, *args, **kwargs):
 86         for key, value in kwargs.items():
 87             setattr(self, key, value)
 88         return super().__init__()
 89 
 90     def save(self):
 91         fields = []
 92         values = []
 93         for key, value in self.fields.items():
 94             db_column = value.db_column
 95             if db_column is None:
 96                 db_column = key.lower()
 97             fields.append(db_column)
 98             value = getattr(self, key)
 99             values.append(str(value))
100 
101         sql = 'insert {db_table}({fields}) value({values})'.format(db_table=self._meta['db_table'], fields=','.join(fields), values=','.join(values))
102         print(sql)
103 
104 
105 class User(BaseModel):
106     name = CharField(db_column='name', max_length=10)
107     age = IntField(db_column='age', min_value=0, max_value=100)
108 
109     class Meta:
110         db_table = 'user'
111 
112 
113 if __name__ == '__main__':
114     user = User()
115     user.name = 'zy'
116     user.age = 21
117     user.save()

insert user(name,age) value(zy,21)