diff options
| -rw-r--r-- | guides/source/debugging_rails_applications.md | 351 |
1 files changed, 218 insertions, 133 deletions
diff --git a/guides/source/debugging_rails_applications.md b/guides/source/debugging_rails_applications.md index a4273d772b..042ffa7d8d 100644 --- a/guides/source/debugging_rails_applications.md +++ b/guides/source/debugging_rails_applications.md @@ -283,20 +283,21 @@ As soon as your application calls the `byebug` method, the debugger will be started in a debugger shell inside the terminal window where you launched your application server, and you will be placed at the debugger's prompt `(byebug)`. Before the prompt, the code around the line that is about to be run will be -shown and the current line is marked by '=>'. Like this: +displayed and the current line will be marked by '=>'. Like this: ``` [1, 10] in /PathTo/project/app/controllers/posts_controller.rb - 1 class PostsController < ApplicationController - 2 # GET /posts - 3 # GET /posts.json - 4 def index - 5 byebug -=> 6 @posts = Post.all - 7 - 8 respond_to do |format| - 9 format.html # index.html.erb - 10 format.json { render json: @posts } + 3: + 4: # GET /posts + 5: # GET /posts.json + 6: def index + 7: byebug +=> 8: @posts = Post.find_recent + 9: + 10: respond_to do |format| + 11: format.html # index.html.erb + 12: format.json { render json: @posts } + (byebug) ``` @@ -307,8 +308,33 @@ processing the entire request. For example: ```bash -@posts = Post.all -(byebug:7) +=> Booting WEBrick +=> Rails 4.1.0 application starting in development on http://0.0.0.0:3000 +=> Run `rails server -h` for more startup options +=> Notice: server is listening on all interfaces (0.0.0.0). Consider using 127.0.0.1 (--binding option) +=> Ctrl-C to shutdown server +[2014-04-11 13:11:47] INFO WEBrick 1.3.1 +[2014-04-11 13:11:47] INFO ruby 2.1.1 (2014-02-24) [i686-linux] +[2014-04-11 13:11:47] INFO WEBrick::HTTPServer#start: pid=6370 port=3000 + + +Started GET "/" for 127.0.0.1 at 2014-04-11 13:11:48 +0200 + ActiveRecord::SchemaMigration Load (0.2ms) SELECT "schema_migrations".* FROM "schema_migrations" +Processing by PostsController#index as HTML + +[3, 12] in /PathTo/project/app/controllers/posts_controller.rb + 3: + 4: # GET /posts + 5: # GET /posts.json + 6: def index + 7: byebug +=> 8: @posts = Post.find_recent + 9: + 10: respond_to do |format| + 11: format.html # index.html.erb + 12: format.json { render json: @posts } + +(byebug) ``` Now it's time to explore and dig into your application. A good place to start is @@ -316,7 +342,8 @@ by asking the debugger for help. Type: `help` ``` (byebug) help -byebug 2.6.0 + +byebug 2.7.0 Type 'help <command-name>' for help on a specific command @@ -337,36 +364,41 @@ To see the previous ten lines you should type `list-` (or `l-`) ``` (byebug) l- + [1, 10] in /PathTo/project/app/controllers/posts_controller.rb 1 class PostsController < ApplicationController - 2 # GET /posts - 3 # GET /posts.json - 4 def index - 5 byebug - 6 @posts = Post.all - 7 - 8 respond_to do |format| - 9 format.html # index.html.erb - 10 format.json { render json: @posts } + 2 before_action :set_post, only: [:show, :edit, :update, :destroy] + 3 + 4 # GET /posts + 5 # GET /posts.json + 6 def index + 7 byebug + 8 @posts = Post.find_recent + 9 + 10 respond_to do |format| + ``` This way you can move inside the file, being able to see the code above and over -the line you added the `byebug` call. Finally, to see where you are in the code -again you can type `list=` +the line where you added the `byebug` call. Finally, to see where you are in +the code again you can type `list=` ``` (byebug) list= -[1, 10] in /PathTo/project/app/controllers/posts_controller.rb - 1 class PostsController < ApplicationController - 2 # GET /posts - 3 # GET /posts.json - 4 def index - 5 byebug -=> 6 @posts = Post.all - 7 - 8 respond_to do |format| - 9 format.html # index.html.erb - 10 format.json { render json: @posts } + +[3, 12] in /PathTo/project/app/controllers/posts_controller.rb + 3: + 4: # GET /posts + 5: # GET /posts.json + 6: def index + 7: byebug +=> 8: @posts = Post.find_recent + 9: + 10: respond_to do |format| + 11: format.html # index.html.erb + 12: format.json { render json: @posts } + +(byebug) ``` ### The Context @@ -387,33 +419,47 @@ then `backtrace` will supply the answer. ``` (byebug) where - #0 PostsController.index - at line /PathTo/project/app/controllers/posts_controller.rb:6 - #1 Kernel.send - at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/base.rb:1175 - #2 ActionController::Base.perform_action_without_filters - at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/base.rb:1175 - #3 ActionController::Filters::InstanceMethods.call_filters(chain#ActionController::Fil...,...) - at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/filters.rb:617 +--> #0 PostsController.index + at /PathTo/project/test_app/app/controllers/posts_controller.rb:8 + #1 ActionController::ImplicitRender.send_action(method#String, *args#Array) + at /PathToGems/actionpack-4.1.0/lib/action_controller/metal/implicit_render.rb:4 + #2 AbstractController::Base.process_action(action#NilClass, *args#Array) + at /PathToGems/actionpack-4.1.0/lib/abstract_controller/base.rb:189 + #3 ActionController::Rendering.process_action(action#NilClass, *args#NilClass) + at /PathToGems/actionpack-4.1.0/lib/action_controller/metal/rendering.rb:10 ... ``` -You move anywhere you want in this trace (thus changing the context) by using -the `frame _n_` command, where _n_ is the specified frame number. +The current frame is marked with `-->`. You can move anywhere you want in this +trace (thus changing the context) by using the `frame _n_` command, where _n_ is +the specified frame number. If you do that, `byebug` will display your new +context. ``` (byebug) frame 2 -#2 ActionController::Base.perform_action_without_filters - at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/base.rb:1175 + +[184, 193] in /PathToGems/actionpack-4.1.0/lib/abstract_controller/base.rb + 184: # is the intended way to override action dispatching. + 185: # + 186: # Notice that the first argument is the method to be dispatched + 187: # which is *not* necessarily the same as the action name. + 188: def process_action(method_name, *args) +=> 189: send_action(method_name, *args) + 190: end + 191: + 192: # Actually call the method associated with the action. Override + 193: # this method if you wish to change how action methods are called, + +(byebug) ``` The available variables are the same as if you were running the code line by line. After all, that's what debugging is. -Moving up and down the stack frame: You can use `up [n]` (`u` for abbreviated) -and `down [n]` commands in order to change the context _n_ frames up or down the -stack respectively. _n_ defaults to one. Up in this case is towards -higher-numbered stack frames, and down is towards lower-numbered stack frames. +You can also use `up [n]` (`u` for abbreviated) and `down [n]` commands in order +to change the context _n_ frames up or down the stack respectively. _n_ defaults +to one. Up in this case is towards higher-numbered stack frames, and down is +towards lower-numbered stack frames. ### Threads @@ -441,12 +487,22 @@ This example shows how you can print the instance_variables defined within the current context: ``` -@posts = Post.all +[3, 12] in /PathTo/project/app/controllers/posts_controller.rb + 3: + 4: # GET /posts + 5: # GET /posts.json + 6: def index + 7: byebug +=> 8: @posts = Post.find_recent + 9: + 10: respond_to do |format| + 11: format.html # index.html.erb + 12: format.json { render json: @posts } + (byebug) instance_variables -["@_response", "@action_name", "@url", "@_session", "@_cookies", - "@performed_render", "@_flash", "@template", "@_params", - "@before_filter_chain_aborted", "@request_origin", "@_headers", - "@performed_redirect", "@_request"] +[:@_action_has_layout, :@_routes, :@_headers, :@_status, :@_request, + :@_response, :@_env, :@_prefixes, :@_lookup_context, :@_action_name, + :@_response_body, :@marked_for_same_origin_verification, :@_config] ``` As you may have figured out, all of the variables that you can access from a @@ -456,11 +512,19 @@ command later in this guide). ``` (byebug) next -Processing PostsController#index (for 127.0.0.1 at 2008-09-04 19:51:34) [GET] - Session ID: BAh7BiIKZmxhc2hJQzonQWN0aW9uQ29udHJvbGxlcjo6Rmxhc2g6OkZsYXNoSGFzaHsABjoKQHVzZWR7AA==--b16e91b992453a8cc201694d660147bba8b0fd0e - Parameters: {"action"=>"index", "controller"=>"posts"} -/PathToProject/posts_controller.rb:8 -respond_to do |format| +[5, 14] in /PathTo/project/app/controllers/posts_controller.rb + 5 # GET /posts.json + 6 def index + 7 byebug + 8 @posts = Post.find_recent + 9 +=> 10 respond_to do |format| + 11 format.html # index.html.erb + 12 format.json { render json: @posts } + 13 end + 14 end + 15 +(byebug) ``` And then ask again for the instance_variables: @@ -477,31 +541,37 @@ TIP: You can also step into **irb** mode with the command `irb` (of course!). This way an irb session will be started within the context you invoked it. But be warned: this is an experimental feature. -The `var` method is the most convenient way to show variables and their values: +The `var` method is the most convenient way to show variables and their values. +Let's let `byebug` to help us with it. ``` -var -(byebug) v[ar] const <object> show constants of object -(byebug) v[ar] g[lobal] show global variables -(byebug) v[ar] i[nstance] <object> show instance variables of object -(byebug) v[ar] l[ocal] show local variables +(byebug) help var +v[ar] cl[ass] show class variables of self +v[ar] const <object> show constants of object +v[ar] g[lobal] show global variables +v[ar] i[nstance] <object> show instance variables of object +v[ar] l[ocal] show local variables ``` This is a great way to inspect the values of the current context variables. For -example: +example, to check that we have no local variables currently defined. ``` (byebug) var local - __dbg_verbose_save => false +(byebug) ``` You can also inspect for an object method this way: ``` (byebug) var instance Post.new -@attributes = {"updated_at"=>nil, "body"=>nil, "title"=>nil, "published"=>nil, "created_at"... +@_start_transaction_state = {} +@aggregation_cache = {} +@association_cache = {} +@attributes = {"id"=>nil, "created_at"=>nil, "updated_at"=>nil} @attributes_cache = {} -@new_record = true +@changed_attributes = nil +... ``` TIP: The commands `p` (print) and `pp` (pretty print) can be used to evaluate @@ -511,8 +581,8 @@ You can use also `display` to start watching variables. This is a good way of tracking the values of a variable while the execution goes on. ``` -(byebug) display @recent_comments -1: @recent_comments = +(byebug) display @posts +1: @posts = nil ``` The variables inside the displaying list will be printed with their values after @@ -528,80 +598,80 @@ execution. Use `step` (abbreviated `s`) to continue running your program until the next logical stopping point and return control to the debugger. -TIP: You can also use `step+ n` and `step- n` to move forward or backward `n` -steps respectively. - You may also use `next` which is similar to step, but function or method calls -that appear within the line of code are executed without stopping. As with -`step`, you may use plus sign to move _n_ steps. +that appear within the line of code are executed without stopping. + +TIP: You can also use `step n` or `next n` to move forwards `n` steps at once. The difference between `next` and `step` is that `step` stops at the next line of code executed, doing just a single step, while `next` moves to the next line without descending inside methods. -For example, consider this block of code with an included `byebug` statement: +For example, consider the following situation: ```ruby -class Author < ActiveRecord::Base - has_one :editorial - has_many :comments +Started GET "/" for 127.0.0.1 at 2014-04-11 13:39:23 +0200 +Processing by PostsController#index as HTML + +[1, 8] in /home/davidr/Proyectos/test_app/app/models/post.rb + 1: class Post < ActiveRecord::Base + 2: + 3: def self.find_recent(limit = 10) + 4: byebug +=> 5: where('created_at > ?', 1.week.ago).limit(limit) + 6: end + 7: + 8: end - def find_recent_comments(limit = 10) - byebug - @recent_comments ||= comments.where("created_at > ?", 1.week.ago).limit(limit) - end -end +(byebug) ``` +If we use `next`, we want go deep inside method calls. Instead, byebug will go +to the next line within the same context. In this case, this is the last line of +the method, so `byebug` will jump to next next line of the previous frame. + ``` -$ rails console -Loading development environment (Rails 4.0.0) ->> author = Author.first -=> #<Author id: 1, first_name: "Bob", last_name: "Smith", created_at: "2008-07-31 12:46:10", updated_at: "2008-07-31 12:46:10"> ->> author.find_recent_comments -/PathTo/project/app/models/author.rb:11 -) -[2, 9] in /PathTo/project/app/models/author.rb - 2 has_one :editorial - 3 has_many :comments - 4 - 5 def find_recent_comments(limit = 10) - 6 byebug -=> 7 @recent_comments ||= comments.where("created_at > ?", 1.week.ago).limit(limit) - 8 end - 9 end +(byebug) next +Next went up a frame because previous frame finished + +[4, 13] in /PathTo/project/test_app/app/controllers/posts_controller.rb + 4: # GET /posts + 5: # GET /posts.json + 6: def index + 7: @posts = Post.find_recent + 8: +=> 9: respond_to do |format| + 10: format.html # index.html.erb + 11: format.json { render json: @posts } + 12: end + 13: end + (byebug) ``` -You are at the end of the line, but... was this line executed? You can inspect -the instance variables. +If we use `step` in the same situation, we will literally go the next ruby +instruction to be executed. In this case, the activesupport's `week` method. ``` -(byebug) var instance -@attributes = {"updated_at"=>"2008-07-31 12:46:10", "id"=>"1", "first_name"=>"Bob", "las... -@attributes_cache = {} -``` +(byebug) step -`@recent_comments` hasn't been defined yet, so it's clear that this line hasn't -been executed yet. Use the `next` command to move on in the code: +[50, 59] in /PathToGems/activesupport-4.1.0/lib/active_support/core_ext/numeric/time.rb + 50: ActiveSupport::Duration.new(self * 24.hours, [[:days, self]]) + 51: end + 52: alias :day :days + 53: + 54: def weeks +=> 55: ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]]) + 56: end + 57: alias :week :weeks + 58: + 59: def fortnights -``` -(byebug) next -/PathTo/project/app/models/author.rb:12 -@recent_comments -(byebug:1) var instance -@attributes = {"updated_at"=>"2008-07-31 12:46:10", "id"=>"1", "first_name"=>"Bob", "las... -@attributes_cache = {} -@comments = [] -@recent_comments = [] +(byebug) ``` -Now you can see that the `@comments` relationship was loaded and -`@recent_comments` defined because the line was executed. - -If you want to go deeper into the stack trace you can move single steps -through your calling methods and into Rails code. This is one of the best ways -to find bugs in your code, or perhaps in Ruby or Rails. +This is one of the best ways to find bugs in your code, or perhaps in Ruby on +Rails. ### Breakpoints @@ -620,18 +690,33 @@ the debugger. _expression_ works the same way as with file:line. +For example, in the previous situation + ``` -(byebug:5) break 10 -Breakpoint 1 file /PathTo/project/vendor/rails/actionpack/lib/action_controller/filters.rb, line 10 +[4, 13] in /PathTo/project/app/controllers/posts_controller.rb + 4: # GET /posts + 5: # GET /posts.json + 6: def index + 7: @posts = Post.find_recent + 8: +=> 9: respond_to do |format| + 10: format.html # index.html.erb + 11: format.json { render json: @posts } + 12: end + 13: end + +(byebug) break 11 +Created breakpoint 1 at /PathTo/project/app/controllers/posts_controller.rb:11 + ``` Use `info breakpoints _n_` or `info break _n_` to list breakpoints. If you supply a number, it lists that breakpoint. Otherwise it lists all breakpoints. ``` -(byebug:5) info breakpoints +(byebug) info breakpoints Num Enb What - 1 y at filters.rb:10 +1 y at /PathTo/project/app/controllers/posts_controller.rb:11 ``` To delete breakpoints: use the command `delete _n_` to remove the breakpoint @@ -639,8 +724,8 @@ number _n_. If no number is specified, it deletes all breakpoints that are currently active. ``` -(byebug:5) delete 1 -(byebug:5) info breakpoints +(byebug) delete 1 +(byebug) info breakpoints No breakpoints. ``` |