在sqlalchemy中使用postgresql xml數據類型

Question

SqlAlchemy通過方言支持大多數數據庫特定的數據類型，但是我找不到任何與postgresql xml列類型一起工作的東西。有人知道一個可行的解決方案嗎？理想情況下，我自己不應該需要自定義列類型實現。

Answer 1

參見：SQLAlchemy TypeDecorator doesn't work

這裏是修改，以處理用於Oracle XMLTYPE使用XML的任何長度，並且允許LXML etree分配到和從類列相同的溶液（無需deparse /重分析從容器類XML ）

# coding: utf-8 
from sqlalchemy import Column, DateTime, Float, ForeignKey, Index, Numeric, String, Table, Text, CLOB 
from sqlalchemy.orm import relationship 
from sqlalchemy.ext.declarative import declarative_base 

from sqlalchemy.sql.functions import GenericFunction 
class XMLTypeFunc(GenericFunction): 
    type=CLOB 
    name='XMLType' 
    identifier='XMLTypeFunc' 


from sqlalchemy.types import TypeDecorator 
from lxml import etree #you can use built-in etree if you want 
class XMLType(TypeDecorator): 

    impl = CLOB 
    type = 'XMLTYPE' #etree.Element 

    def get_col_spec(self): 
     return 'XMLTYPE' 

    def bind_processor(self, dialect): 
     def process(value): 
      if value is not None: 
       return etree.tostring(value, encoding='UTF-8', pretty_print='True') 
       #return etree.dump(value) 
      else: 
       return None 
     return process 

    def process_result_value(self, value, dialect): 
     if value is not None: 
      value = etree.fromstring(value) 
     return value 

    def bind_expression(self, bindvalue): 
     return XMLTypeFunc(bindvalue) 

Answer 2

如果您需要在PostgreSQL數據庫原生「XML」數據類型，你需要寫從UserDefinedType沒有從TypeDecorator繼承自定義類型。 Documentation

這是我的項目之一使用：

class XMLType(sqlalchemy.types.UserDefinedType): 
    def get_col_spec(self): 
     return 'XML' 

    def bind_processor(self, dialect): 
     def process(value): 
      if value is not None: 
       if isinstance(value, str): 
        return value 
       else: 
        return etree.tostring(value) 
      else: 
       return None 
     return process 

    def result_processor(self, dialect, coltype): 
     def process(value): 
      if value is not None: 
       value = etree.fromstring(value) 
      return value 
     return process