Using postgresql xml data type with sqlalchemy

Question

SqlAlchemy supports most database specific data types via dialects, but I could not find anything to work with the postgresql xml column type. Does somebody know a working solution. Idealy it should not require a custom column type implementation by myself.

Answer 1

If you need to have native 'xml' data type in postgresql database, you need to write custom type which inherited from UserDefinedType not from TypeDecorator. Documentation

Here is what I used in one of the projects:

import xml.etree.ElementTree as etree
import sqlalchemy

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