PostgreSQL XML data and Elixir / Ecto?

silverdr

Any well established methods of handling XML data from / to PostgreSQL xml columns using Ecto? How do Elixir veterans do it? If they do, of course…

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#ecto #xml

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2026-01-24 15:59:44 UTC

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christhekeele

AFICT, nothing in the ecosystem today (postgrex nor extensions/peers) supports postgres xml types, functions, or queries.

For types, you can use custom Ecto.Types to handle serialization between PG and Elixir. For DDLs, I’d just write my migrations in straight SQL strings, executed by Repo.query! rather than a DSL.

For functions and queries, you’re going to want to use fragments. Essentially, escaping the pure data-modelling of Ecto to insert raw SQL into an otherwise safely Ecto-built query.

This is similar to what I do in my python projects that use XML columns, and it works fairly well. Our use-case is write-once query-occasionally so it’s fairly trivial: we rarely need to read the full document into memory once inserted, and never need to update it.

More integrated functionality would require more work. Perhaps a library calling out to be made?

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dimitarvp

I am joining @christhekeele here – f.ex. using :xmerl is maddening because it has a nice low-level streaming interface (among others!) because on the one hand, 95% of the code is exactly the same… but the other 5% vary every frakkin time. This really makes it very difficult to extract out libraries. I entertained the idea but ultimately concluded it would add too little value for what would basically be just one instance of a SAX parser with the ability to pass “callbacks” to it… something everyone can roll in literal one hour maximum.

Post #9

dimitarvp

As the efficiency maniac that I will always be, I’d use Erlang’s :xmerl even if I know no XML content would ever be more than 20KB.

But I am not aware of a library that directly adds a custom Ecto.Type for it, no.

Post #2

silverdr

Roger, thank you. I’ll have to sculpt something out of it. I didn’t say it’s not possible but that nothing I found is “full-fledged” as in “handles all both ways”. Things are scattered, and there are bits and pieces here and there. Even with your suggestions – where you surely have done these type of things before – it’s still three different libs, including an Erlang one. I’d dream of something like e. g. JSON.decode, JSON.encode, as XML.de/encode, augmented with XML.validate and XML Ecto type. Anyway - it is what it is.

Hehe… Yes, I know. Been there, seen that. Not in Elixir though

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Schultzer

Yeah, my Postgres driver is going to support anything out of the box, as any type even custom types in the end can be decoded to their base type, for XML it would be text.

But we probably want more then just text if we’re going to do more work with it in our application code.

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