Best way to handle clojure exceptions and why my exception is not being caught inside go block
I am trying to find the best way to handle exceptions in clojure, I use https://github.com/alaisi/postgres.async which threw exeption on failure, but I would rather return false (because I am using a validator) or even better that something like Either a monad (or something simpler like this http://adambard.com/blog/acceptable-error-handling-in-clojure/ )
1) I am trying to catch the exception and if there is return return false, but the code does not work (does not return false and throws an exception).
(try
(dosql [tx (<begin! db)
ucount (<execute! tx ["UPDATE groups SET garticlescounter=garticlescounter + 1 WHERE gid=$1"
groupid])
uartc (<execute! tx ["UPDATE subtopics SET starticlescount=starticlescount + 1 WHERE stid=$1"
sid])
uartins (<insert! tx
{:table "articles"}
{:aurl url :atitle title :asuttopicid sid :acommentcount 0 :alikescount 0 :auid uid})
ok? (<commit! tx)]
ok?)
(catch Exception _ false))
2) Could it be possible to wrap in such a way that if the job returned ok? and if doesnt work, returns false, or maybe [ok? nil] and [nil error] macro possible?
---- thanks swinn I did it
;must receive an optional parameter for error response or
; build a [nil ok] response but just know this works for me...
(defmacro async-try-block! [block]
`(let [chn# (!/chan 1)]
(!/go
(let [response# (try
~block
(catch Throwable e#))]
(if (instance? Throwable response#) (!/put! chn# false) (!/put! chn# response#))))
chn#))
(async-try-block!
(dosql [tx (<begin! db)
ucount (<execute! tx ["UPDATE groups SET garticlescounter=garticlescounter + 1 WHERE gid=$1"
groupid])
uartc (<execute! tx ["UPDATE subtopics SET starticlescount=starticlescount + 1 WHERE stid=$1"
sid])
uartins (<insert! tx
{:table "articles"}
{:aurl url :atitle title :asuttopicid sid :acommentcount 0 :alikescount 0 :auid uid})
ok? (<commit! tx)]
ok?))
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I am not familiar with the postgres.async library but is Exception
not the root of all Exceptions in the JVM, Throwable
is.
Changing your catch to Throwable
would be the first change I would suggest, but it looks like it (<execute! ...)
actually gets the exception for you and returns it, so you need to check the return value with(instance? Throwable)
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