Add immutable version of ash_raise_error function to support extensions like Citus
#620
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| def drop(2) do | ||
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| #{ash_raise_error()} |
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So I like this, but I also hesitate to define this function automatically in everyone's databases when its only need by a few. My suggestion would be to create a new "extension" (not an Ash extension, just one of these postgres extension modules) that users can optionally add to define this function. |
stevebrambilla
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| ``` | ||
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| use AshPostgres.CustomExtension, name: "immutable_raise_error", latest_version: 1 |
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This would be the first AshPostgres.CustomExtension offered by AshPostgres — is this what you had in mind, or would you prefer special-casing this in the migrator like "ash-functions" and using a string value for it?
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No need to special case, "ash-functions" existed before we had this.
lib/sql_implementation.ex
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| # Conditionally apply @impl to keep compatibility across ash_sql versions | ||
| if {:immutable_errors?, 1} in AshSql.Implementation.behaviour_info(:callbacks) do |
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Maybe this is overkill? Would you prefer to just bump the AshSql dependency to the next release?
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Yeah let's just bump it. For now, replace the dep with a dependency on ash_sql main and we can get it merged, and then hex will make me point at a proper version before releasing.
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Sounds good, done!
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🚀 Thank you for your contribution! 🚀 |
We use the Citus extension for sharding our Postgres database, which adds a requirement that any functions used within CASE or COALESCE expressions must be IMMUTABLE. Currently this means that we can't use error expressions at all because
ash_raise_erroris currently marked as STABLE.The current
ash_raise_errorcould technically be IMMUTABLE as it meets all of the requirements. However, the postgres planner will constant-fold the function call, making all expressions that use it immediately raise an exception. To prevent this we need to make the function call dependent on the row so it can't be constant-folded.This PR adds a new function,
ash_raise_error_immutable, that is marked IMMUTABLE and accepts a third argument that is simply ignored. This works together with a change in AshSql that adds a row-dependent argument, preventing the caching.It's opt-in only via an
AshPostgres.Repocallback, which stores a value in the repo config. AshSql looks for that config value when building the query and decides whether to call the existingash_raise_errorfunction, or the newash_raise_error_immutable.Related AshSql PR: ash-project/ash_sql#175
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