How to fix 2200L: not_an_xml_document in PostgreSQL

Review the failing SQL statement to determine whether it uses XMLPARSE(DOCUMENT ...), an implicit cast to xml (which respects xmloption), or an XML function like XMLTABLE. Look at the actual XML string that triggered the error. Check whether the input contains multiple top-level elements, DOCTYPE declarations, or processing instructions. These are valid XML but not valid DOCUMENT form in PostgreSQL.

Run xml_is_well_formed_content against the same string to confirm whether libxml recognizes it as valid XML (ignoring DOCUMENT restrictions):

SELECT xml_is_well_formed_content('<item>1</item><item>2</item>');
SELECT xml_is_well_formed_content('<?xml version="1.0"?><root/>');

If the function returns true, the XML is valid but violates DOCUMENT restrictions. If it returns false, the XML is actually malformed and you should switch to fixing 2200M instead.

If you have a well-formed XML fragment and do not need it to be a strict document, switch from XMLPARSE(DOCUMENT ...) to XMLPARSE(CONTENT ...):

-- Before (fails with 2200L):
SELECT XMLPARSE(DOCUMENT '<item>1</item><item>2</item>');

-- After (succeeds):
SELECT XMLPARSE(CONTENT '<item>1</item><item>2</item>');

CONTENT mode allows fragments, multiple root elements, and processing instructions, so 2200L will not be raised.

If you must store XML as a document (e.g., in an xml column with xmloption set to DOCUMENT) but your input is a fragment, wrap the content in a synthetic root using xmlelement or xmlconcat:

SELECT XMLPARSE(DOCUMENT xmlelement(name root, XMLPARSE(CONTENT '<item>1</item><item>2</item>')));

-- Or using xmlconcat:
SELECT XMLPARSE(DOCUMENT xmlconcat(
  XMLPARSE(CONTENT '<item>1</item>'),
  XMLPARSE(CONTENT '<item>2</item>')
));

This creates a single root element that satisfies DOCUMENT requirements while preserving your content.

If your application frequently inserts or casts XML fragments, set the session xmloption to CONTENT before performing the operations:

SET xmloption TO CONTENT;

CREATE TABLE xml_data (
  id SERIAL PRIMARY KEY,
  payload XML
);

INSERT INTO xml_data (payload) VALUES ('<item>1</item><item>2</item>');

This globally allows CONTENT mode for all implicit casts and operations in the session. Use DOCUMENT only when you truly require single-root documents.

If the XML contains a DOCTYPE declaration and you control the source, strip it before passing to PostgreSQL:

-- PostgreSQL XMLPARSE does not accept DOCTYPE
SELECT XMLPARSE(DOCUMENT '<!DOCTYPE root [...] ><root/>');
-- Raises 2200L

-- Remove the DOCTYPE:
SELECT XMLPARSE(DOCUMENT '<root/>');
-- Succeeds

If the DOCTYPE is meaningful, store it separately as plain text and reattach it when exporting XML to clients.