On Thursday, May 14, 2020 at 10:40:20 AM UTC-7, Troex Nevelin wrote:
>
> Hi Jeremy,
>
> We are heavily using Sequel in PostgreSQL (dev/staging) / Redshift (prod)
> environment, so sometimes we have to keep adapter specific code, and
> recently some expressions where added like this:
>
> module Sequel
> # a NULL-safe "not equal" comparison condition
> # (
> # (a IS NULL AND b IS NOT NULL) OR
> # (a IS NOT NULL AND b IS NULL) OR
> # (a <> b)
> # )
> def self.is_distinct_from(a, b)
> if defined?(DB) == 'constant' && DB.adapter_scheme == :redshift
> (Sequel[a] =~ nil) & (Sequel[b] !~ nil) |
> (Sequel[a] !~ nil) & (Sequel[b] =~ nil) |
> (Sequel[a] !~ Sequel[b])
> else
> Sequel.lit('? IS DISTINCT FROM ?', a, b)
> end
> end
>
> module Timezones
> def timezone_fn(timezone, field)
> fn = if defined?(DB) == 'constant' && DB.adapter_scheme == :redshift
> 'CONVERT_TIMEZONE'
> else
> 'timezone'
> end
>
> Sequel.lit("#{fn}(?, ?)", timezone, field)
> end
> end
> end
>
> It works, but it's not very nice momkey-patching, can point me to some
> example in the code - the way it should be done properly?
> I tried to add it into SQL Builders module but it didn't work for me,
> probably I missed something.
>
You should have is_distinct_from return an object that implements
sql_literal_append(dataset, sql). You can then use
"dataset.db.adapter_scheme == :redshift" to check for Redshift. You would
then append the appropriate SQL code to the given string (sql). I think
the same approach could be used for timezone_fn.
We keeping a fork of "working for us" redshift adapter for sequel here
> https://github.com/attribution/sequel-redshift
> <https://github.com/attribution/sequel-redshift/commit/8d2828706970c6fd7661909315b5eecde9759bb7#diff-05c70fb8a8093e49de9c56c14213044cR125>
>
> Btw had to copy whole class here just to add ":redshift" to the case
> statement:
>
> https://github.com/attribution/sequel-redshift/commit/8d2828706970c6fd7661909315b5eecde9759bb7#diff-05c70fb8a8093e49de9c56c14213044cR125
>
If you look at the top of the function, you'll see it does:
if defined?(super)
return super
end
So you just need to override Dataset#string_agg_sql_append in your redshift
adapter and the string_agg extension will call it automatically.
Thanks for your hard work on sequel, our new devs hate it at first, but
> couple months later they can't live without it anymore ;) Great gem!
>
That's good to hear. I would be great if they didn't hate it at first. :)
Thanks,
Jeremy
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