Does Ash support defining exclusion constraints on resources with the DSL?

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1

Does Ash support defining exclusion constraints on resources with the DSL (maybe that’s a Postgres specific thing?).

I’m wanting to enforce non-overlapping appointment times. It may be that I need to just write custom SQL, which, I think is how it’s done in Ecto currently if you want to do it.

2

There is no way to do it using any of the builtin ones (like check_constraint), but you can at least manage it in the resource using custom_statements.

The example for that is here:

https://hexdocs.pm/ash_postgres/dsl-ashpostgres-datalayer.html#postgres-custom_statements

But I’ll copy it over for reference:

custom_statements do
  # the name is used to detect if you remove or modify the statement
  statement :pgweb_idx do
    up "CREATE INDEX pgweb_idx ON pgweb USING GIN (to_tsvector('english', title || ' ' || body));"

    down "DROP INDEX pgweb_idx;"
  end
end
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3

Keep in mind that with custom_statements sometimes you will need to manually reorder the statements in your migration, i.e if it refers to a field you are adding or something like that.

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4

Oh, is that so I don’t have to go manually add it into the migration file by hand? So when I generate migrations it gets inserted? That’s super helpful.

5

And what is this used for? Looks like building custom error strings for when there is an exclusion error?

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6

That is used for expressing a list of exclusion constraints that exist that may raise errors, so if you add an exclusion constraint you should add the name there so you get a nice error.

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7

Excellent, this gets me off to a good start.