SQLAlchemy declaring custom UserDefinedType for XML in MSSQL

Question

I am trying to declare a custom type of "XMLType" for use with MSSQL. But I keep getting 'AttributeError: module 'app.db.XMLType' has no attribute '_set_parent_with_dispatch''. I don't see anything that isn't declared correctly in my XMLType class file.

import sqlalchemy.types as types

from lxml import etree

class XMLType(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

I am basing the code off of http://docs.sqlalchemy.org/en/latest/core/custom_types.html?highlight=get_col_spec#sqlalchemy.types.UserDefinedType and Using postgresql xml data type with sqlalchemy.

Please provide a) full tracebacks b) proper minimal, complete and verifiable example. Where and how were you using your custom type when you got the error? — Ilja Everilä, Apr 11 '17 at 11:02

score 1 · Accepted Answer · answered Apr 11 '17 at 14:27

So there happened to be something wrong with my import. For my model I originally had the following:

from sqlalchemy import Column, Integer, String, DateTime
from sqlalchemy.ext.declarative import declarative_base
import conductor.db.XMLType as XML

Base = declarative_base()

class Raw_data_records(Base):
    __tablename__ = 'raw_data_records'

    id = Column('id', Integer, primary_key=True, autoincrement=True)
    basename = Column('basename', String)
    filename = Column('filename', String)
    file_size = Column('file_size', Integer)
    machine = Column('machine', String)
    insert_timestamp = Column('insert_timestamp', DateTime)
    raw_xml = Column('raw_xml', XML)

I then changed my import to:

from spcconductor.db.XMLType import XMLType and the raw_xml = Column('raw_xml', XML) to raw_xml = Column('raw_xml', XMLType) and it worked.

For anyone that needs the information this is the XMLType.py (I have not tested it...):

import sqlalchemy.types as types

from lxml import etree

class XMLType(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

SQLAlchemy declaring custom UserDefinedType for XML in MSSQL

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