# _*_ coding:utf-8 _*_
from django.db import models
import ast


class ListField(models.TextField):
  """自定義list字段
  models.SubfieldBase  提供to_python  和 from_db_value
  把數(shù)據(jù)庫數(shù)據(jù)轉(zhuǎn)化成python數(shù)據(jù)
  現(xiàn)在主要是from_db_value 方法 把數(shù)據(jù)庫數(shù)據(jù)轉(zhuǎn)化成python數(shù)據(jù)
  to_python 主要是接受form表單
  """
  __metacalss__ = models.SubfieldBase
  description = 'Stores a python list'

  

def __init__(self, *args, **kwargs):

    super(ListField,self).__init__(*args, **kwargs)

  # def db_type(self, connection):
  #   if connection.setting_dict['ENGINE'] == 'django.db.backends.mysql':
  #     return 'listtype'
  

 def from_db_value(self,value,expression,connection,context):

  """數(shù)據(jù)庫數(shù)據(jù)轉(zhuǎn)成python數(shù)據(jù)"""

    if value is None:
      value=[]
      return value
    if isinstance(value,list):
      return value
    return ast.literal_eval(value)


  def to_python(self, value):
    """從數(shù)據(jù)庫中讀取的數(shù)據(jù)轉(zhuǎn)成python
    eval（value）讀取value原來的類型
    ast模塊就是幫助Python應(yīng)用來處理抽象的語法解析的。
    而該模塊下的literal_eval()函數(shù)：
    則會(huì)判斷需要計(jì)算的內(nèi)容計(jì)算后是不是合法的python類型，
    如果是則進(jìn)行運(yùn)算，否則就不進(jìn)行運(yùn)算。
    """
    if not value:
      value = []
    if isinstance(value, list):
      return value
    return ast.literal_eval(value)

  def get_prep_value(self, value):
    """
    把python數(shù)據(jù)壓縮后保存到數(shù)據(jù)庫
    或者說把python對(duì)象轉(zhuǎn)化成查詢值
    返回值是個(gè)字符串
    :param value:
    :return:
    """
    if value is None:
      return value
    return str(value)

  # def get_db_prep_value(self, value, connection, prepared=False):
  #   """把查詢集數(shù)據(jù)轉(zhuǎn)化成數(shù)據(jù)庫值  一般不需要重寫 只需要覆蓋"""
  #   value = super(ListField, self).get_db_prep_value()
  #   if value is not None:
  #     return connection.Database.Binary(value)
  #   return value
  #

  def get_prep_lookup(self, lookup_type, value):
    """限制查詢方式"""
    if lookup_type == 'exact':
      return value
    elif lookup_type == 'in':
      return [self.get_prep_value(v) for v in value]
    else:
      return TypeError('lookup type %r not supported'%lookup_type）
  

def value_to_string(self, obj):

    """轉(zhuǎn)換字段數(shù)據(jù)以進(jìn)行序列化
    Field._get_val_from_obj(obj) 是獲取值序列化的最佳方式
    """
    value = self._get_val_from_obj(obj)
    return self.get_db_prep_value(value)