JerryBels
Hi 
In my umbrella app, with currently two apps, each based on its own DB…
I have a schema in app2 referencing a uuid from an object of app1 .
DB1 :
Table : parent
parent_id: uuid
name: string
DB2 :
Table : child
child_id: uuid
parent_id: uuid
name: string
Then the schema :
schema "child" do
field :name, :string
belongs_to(:parent, Parent, type: :binary_id)
timestamps()
end
How to have the changeset validate that parent_id is valid and exists in its table ? I tried some things, like assoc_constraint(:parent) but tbh I knew it wouldn’t work… Maybe I just should rethink the relationship and how it works.
Thanks ahead.
Where Next?
Trending in Questions
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
Error tracking, logs, APM, uptime and cron monitoring in one dev-friendly platform. Find and fix problems before your users notice.
Categories:
Sub Categories:
Forums
Popular Tags
- #ecto
- #liveview
- #troubleshooting
- #learning-elixir
- #deployment
- #library
- #erlang
- #testing
- #genserver
- #mix
- #absinthe
- #remote-other
- #otp
- #plug
- #how-to-question
- #macros
- #postgres
- #elixirconf
- #channels
- #exunit
- #discussion
- #code-sync
- #javascript
- #podcasts
- #onsite
- #dialyzer
- #docker
- #authentication
- #umbrella
- #full-time-contract
- #podcasts-by-brainlid
- #ecto-query
- #blog-post
- #elixir-ls
- #ai
- #elixirconf-us
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #api
- #forms
- #hex
- #security
- #metaprogramming
Our Sponsors
Build Elixir applications with speed and confidence.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Error tracking, logs, uptime, and Just Enough APM. Built for developers.
Elixir, Erlang & BEAM conferences from Code Sync - join us in 2026!
Practical resources that improve the lives of professional developers.
Master modern tools, write cleaner code, and tackle real-world challenges.
Bringing learning, work and compliance together since 1987.
The team behind Membrane, Popcorn, LiveDebugger. Available for hire.
Courses that'll move you from confusion to "Aha, now I get it!"
Showing Posts 1 to 5- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
hauleth
You cannot have cross DB relations. If
parentrecords aren’t deleted, then you can do it by additional query, if they can be deleted, then there is no way to check it and be 100% sure that there will not be difference.JerryBels
I know corss DB FKs are not possible. The question is, how to validate efficiently the changeset in that case ? I was thinking of a custom validation function, that would go and request what is needed, returning false when need to… But then, surely it won’t be located in the changeset. So, if it’s the right way, where should it belongs ?
LostKobrakai
Why wouldn’t it belong in the changeset? If you need to call to a external service as part of validating the changeset then it is that way.
JerryBels
I just don’t like the idea of the changeset having some logic linked to another table… But again, I’m only starting with functionnal programming so I could be wrong.
peerreynders
If I understand the situation correctly … changeset is just a data structure. Custom validation is typically performed with
validate_change/3which is handed avalidatorfunction. And while that function’s arguments are only the field name and value, a function expression has access to anything in the enclosing scope.So with
validate_changeyou can involve any functionality in the validation process.It’s probably also worthwhile to mention that
foreign_key_constraint/3andunique_constraint/3don’t actually check the constraint at the time the function is called. They simply “prepare” the changeset - so if a DB-level constraint error occurs within theRepooperation the error can be readily converted to the appropriate changeset error (suppressing the exception).