On May 20, 4:42 pm, Jeremy Evans <[email protected]> wrote:
.
>
> If you have questions about the best way to accomplish something in
> Sequel for a given snippet of ActiveRecord code, please post here.
>
Thank-you very much. I am writing a new project using Rails and have
some misgivings about AR's approach to SQL and RDBMS in general. I
have selected PostgreSQL as the backend and there are a lot of things
available in PG that AR makes difficult to use. So I am considering
replacing AR before I become too bound to its implementation specific
attributes.
The most recent case was a need to report the most recent N records in
each category from a table that contained multiple categories. I
ended up with SQL that looked like this:
-- Selects most recent exchange rate for all currencies
-- Change LIMIT value to N to get N most recent rates
SELECT *
FROM currency_exchange_rates AS xchg1
WHERE id
IN (
SELECT id
FROM currency_exchange_rates as xchg2
WHERE
xchg1.currency_code_base = xchg2.currency_code_base
AND
xchg1.currency_code_quote = xchg2.currency_code_quote
ORDER BY currency_code_base,
currency_code_quote,
effective_from DESC
LIMIT 1 )
ORDER BY currency_code_base,
currency_code_quote,
effective_from DESC
I basically had to pass this code to AR.find_by_sql() as a string,
using "#{}" to substitute the LIMIT value dynamically. I am not sure
if any ORM is capable of dealing with this sort of construct. It
seemed to me as if there was no other way to do it with AR, short of
reading the entire table into an array and doing the sorting and
selecting inside Ruby. How would SEQUEL do it?
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