If I have a loop, and somewhere in the loop, I get an exception or error. How do I keep the loop going?
Foos.each do |foo|
....
# Random error/exception thrown here
....
end
Should I have a rescue block in the loop? Will that make the loop finish? Or is there a better alternative?
You can use add a begin/rescue block. I am not sure there is other ways to do keep loop going if an error is raised.
4.times do |i|
begin
raise if i == 2
puts i
rescue
puts "an error happened but I'm not done yet."
end
end
# 0
# 1
# an error happened but I'm not done yet.
# 3
#=> 4
Since your title in the other hand ask for a way to ends the loop.
If you want the loop to ends in the rescue, you can use break.
4.times do |i|
begin
raise if i == 2
puts i
rescue
puts "an error happened and I'm done."
break
end
end
# 0
# 1
# an error happened and I'm done.
#=> nil
Related
I have a method like so:
def self.perform
total_done = 0
all_user_roles = UserRole.all
user_roles_count = all_user_roles.count
Rails.logger.info "Going to loop #{user_roles_count} times"
all_user_roles.each do |user_role|
Rails.logger.info "starting the loop..."
if user_role.invalid?
Rails.logger.info "Skipping, role invalid."
next
end
role_name = RoleService.send(
:role_name,
role: user_role[:role],
project: user_role.project
)
existing_role = RoleService.get_for_user(user_role.user, project: user_role.project)
if existing_role.present?
Rails.logger.info "Skipping role because it already exists."
next
end
RoleService.set_for_user(
user_role.user,
project: user_role.project
)
migrated_roles += 1
end
Rails.logger.info "DONE"
rescue StandardError => e
Rails.logger.error("Error!")
end
To my surprise, I see it should loop 1000 times:
>>> Going to loop 1000 times
...but neither the DONE message nor the Error at the end are logged. I see it runs 105 times, and then no more messages in the log.
What could be happening here? Is there a way for something to be raised from one of those service calls and not be caught by the general rescue at the end?
I'm running out of ideas...
Thanks!
Given something like this
def infinite
puts Time.now
rescue => err
puts err.message
ensure
infinite
end
When you run this in console/rake and hit ctrl-c - nothing happens. How do you escape this with CTRL-C?
Use catch instead which is an alternative control flow.
catch executes its block. If throw is not called, the block executes normally, and catch returns the value of the last expression evaluated.
Ruby searches up its stack for a catch block whose tag has the same object_id as the throw (symbols are almost always used as the have the same object_id). When found, the block stops executing and returns val (or nil if no second argument was given to throw).
def infinate
catch(:done) do
begin
infinite
rescue SystemExit, Interrupt => e
puts e.message
throw :done
end
end
end
Using ensure with a condition like that is semantically wrong as the whole point of ensure is to run code that always should be run.
Using rescue to create an infinite loop via recursion seem overly complicated and could cause a SystemStackError later on.
Why not use an actual loop:
def infinite
loop do
begin
puts Time.now
rescue => err
puts err.message
end
end
end
With the above, Ctrl-C works just fine, because rescue without an explicit exception class will only handle StandardErrors.
I'm not sure if this is the proper solution but this worked for me:
def infinite
puts Time.now
rescue SystemExit, Interrupt
#skip_ensure = true
puts 'SystemExist/Interrupt'
rescue => err
puts err.message
ensure
infinite unless #skip_ensure
end
Is there a way to find out whether any exception was raised and rescued during the execution of some code?
Preferably in tests written with ActiveSupport::TestCase and not RSpec
Is there any global ruby exception stack or something, which I could check?
If you want to be a monster, you can instrument the errors themselves:
class StandardError
##called = false
def initialize
##called = true
super
end
def self.called
##called
end
end
#test it out like so:
def raise_arg_error
raise ArgumentError
rescue
end
puts ArgumentError.called #false
raise_arg_error
puts ArgumentError.called #true
Great for ad hoc sanity checks. Terrible for production code.
As clarified in the comments, OP needed it for debug purposes as opposed to write tests with it.
Kernel#set_trace_func lets you intercept low level events such as an error being raised:
set_trace_func(proc do |event, *_|
puts 'Raised!' if event == 'raise'
end)
raise 'Oh, no!' rescue :foo
You can run #set_trace_func before the code you were trying to debug. If no exception was raised, but a raise was registered by the hook - someone rescued it.
This can create some noise depending on what you are executing. Fortunately, you can filter it down by file and line:
set_trace_func(proc do |event, file, line, *_|
if event == 'raise' && file == 'test.rb' && line == 42
puts "Raised on #{file}:#{line}!"
end
end)
It even gives you the binding, so you can drop down a debugger:
require 'irb'
set_trace_func(proc do |event, *_, error_binding, _|
error_binding.irb if event == 'raise'
end)
def foo
bar = 42
raise 'Oh, no!' rescue :baz
end
foo
# Opens an irb
# > bar # => 42
I have a loop like this:
# Iterate a list of items
req_wf_list.each do |req_wf|
# Begin a transaction
ReqWf.transaction do # ReqWf is an ActiveRecord model class
# Do some things
# ...
# 1. I want to be able to continue processing with the
# next iteration of the loop if there is an error here
# 2. I also want to rollback the transaction associated with
# this particular iteration if I encounter an error
begin
# Do something that might return an error
rescue
# Do some error processing
puts "Caught such and such error"
# Don't complete transaction (rollback),
# don't "do some more things",
# proceed to next item in req_wf_list
next
end
# Do some more things
# Shouldn't make it here if there is an error but I do indeed make it here
# ...
# End transaction
end
# End loop
end
Now, I would expect that calling "next" within the rescue block would cause the transaction associated with that particular iteration of the loop to rollback and for execution to resume at the top of the next iteration of the loop. Instead, execution appears to resume at the "Do some more things" line. It is as if the "next" statement is completely ignored. What am I missing?
Most likely that in this case next applies to transaction so you are in a nested loop situation.
This is an example of what can be done to solve the issue
req_wf_list.each do |req_wf|
catch :go_here do #:missingyear acts as a label
ReqWf.transaction do
throw :go_here unless something #break out of two loops
end
end #You end up here if :go_here is thrown
end
But in general, it is not a good practice to use next. You should be able to put a global begin .. rescue and have all the conditions inside of it, so that nothing else gets executed once you catch an error.
Update
I did some a small test and the behavior is as you expect it.
loop = [1,2,3]
loop.each do |value|
puts "value => #{value}"
ActiveRecord::Base.transaction do
puts "Start transaction"
begin
raise
rescue
puts "ActiveRecord::StatementInvalid"
next
end
puts "Should not get here!"
end
end
The output is the following:
value => 1
Start transaction
ActiveRecord::StatementInvalid
value => 2
Start transaction
ActiveRecord::StatementInvalid
value => 3
Start transaction
ActiveRecord::StatementInvalid
Is it possible that you had another error in your code before the next was being called ?
In any case, using the next statement is not the best option as I said before.
I have an array like this
a = []
a << B.new(:name => "c")
a << B.new(:name => "s")
a << B.new(:name => "e")
a << B.new(:name => "t")
How i can save it at once?
B.transaction do
a.each(&:save!)
end
This will create a transaction that loops through each element of the array and calls element.save on it.
You can read about ActiveRecord Transactions and the each method in the Rails and Ruby APIs.
a.each(&:save)
This will call B#save on each item in the array.
So I think we need a middle ground to Alexey's raising exceptions and aborting the transaction and Jordan's one-liner solution. May I propose:
B.transaction do
success = a.map(&:save)
unless success.all?
errored = a.select{|b| !b.errors.blank?}
# do something with the errored values
raise ActiveRecord::Rollback
end
end
This will give you a bit of both worlds: a transaction with rollback, knowledge of which records failed and even gives you access to the validation errors therein.
Wrapping save in transaction will not be enough: if a validation is not passed, there will be no exception raised and no rollback triggered.
I can suggest this:
B.transaction do
a.each do |o|
raise ActiveRecord::Rollback unless o.save
end
end
Just doing B.transaction do a.each(&:save!) end is not an option either, because the transaction block will not rescue any exception other than ActiveRecord::Rollback, and the application would crash on failed validation.
I do not know how to check afterwards if the records have been saved.
Update. As someone has downrated my answer, i assume that the person was looking for a cut-and-paste solution :), so here is some (ugly :)) way to process fail/success value:
save_failed = nil
B.transaction do
a.each do |o|
unless o.save
save_failed = true
raise ActiveRecord::Rollback
end
end
end
if save_failed
# ...
else
# ...
end
I know this is an old question but I'm suprised no one thought of this:
B.transaction do
broken = a.reject { |o| o.save }
raise ActiveRecord::Rollback if broken.present?
end
if broken.present?
# error message
end
In case you're looking for more efficient solution than save each row in the loop please look my answer here Ruby on Rails - Import Data from a CSV file
I'm suggesting to use gem activerecord-import there.