Database Issues

Suppose you had the index of pets open in your browser and 0:00 you clicked the link to open the show page for one of them in a new tab. 0:03 You do some random browsing and 0:08 then go back to the first tab and click the delete link for that pet. 0:12 Some more random browsing. 0:18 And then you go back to the show page tab and click Reload. 0:20 You'll get this error, ActiveRecord::RecordNotFound. 0:24 What should you do in this case? 0:27 Possibly nothing. 0:29 The record is missing because it's supposed to be. 0:30 You deleted it, after all. 0:32 In the rare event that something similar happens in production, 0:34 rather than a RecordNotFound error, 0:37 your users will see a 404 page indicating they tried to access a nonexistent page. 0:39 If you want finer control over these errors, 0:45 though, one thing you can do is to rescue the exception. 0:47 We can go into app/controllers/pets_controller.rb, 0:50 find the show action, and edit it to add a rescue clause to rescue the exception. 0:53 So we can say rescue ActiveRecord::RecordNotFound, 1:00 since that's the exception we were getting. 1:10 In the event that we get such an error, we can put up a flash 1:12 message of type notice, saying we couldn't find that pet. 1:18 And then we can redirect users back to the index of all pets. 1:28 Save that, and let's try reloading the page with the missing pet. 1:34 Reload it and we get redirected back to the index of all pets with a flash 1:40 message, we couldn't find that pet. 1:44 You'll have to decide which is right for your app, 1:48 explicitly handling load errors or just letting it show a 404 page. 1:50 The ability to explicitly handle errors is there if you want it, though. 1:54 Sometimes, RecordNotFound errors can be more serious, though. 1:58 Suppose we were getting this error every time we clicked an Edit link for a pet. 2:02 ActiveRecord::RecordNotFound Couldn't find pet with ID, and nothing. 2:07 And if we look in the stack trace, we see this is occurring at 2:13 app/controllers/pets_controller.rb line 26 in the edit method. 2:15 Let's try opening the file mentioned in the stack trace and see what we find. 2:21 We'll open app/controllers/pets_controller.rb and 2:24 we'll go to line 26. 2:30 The problem seems to be with that call to Pet.find but 2:32 maybe you can't see what it is just yet. 2:35 Let's take another look at the error. 2:38 It says, couldn't find pet with ID, blank. 2:39 It seems like there should be an ID number after 'id'=. 2:44 That's a little strange. 2:47 Let's take a look at exactly what we're passing to Pet.find. 2:49 Rails apps have a logger object which writes text messages to your terminal 2:53 and to a file. 2:57 All those messages you've seen regarding GET and POST requests, errors, 2:58 and so on were displayed by the logger. 3:02 And you can display your own messages using the logger too. 3:05 You can call the logger method within the code for any Rails controller, 3:08 model, or mailer. 3:12 That'll return a logger object, 3:13 and there are several methods that you can call on that object. 3:15 All these methods take a string and add it to the log. 3:19 The difference is how important that message is. 3:22 Debug messages aren't very important and 3:25 should only be included in the log when debug mode is turned on. 3:27 Info messages have information about what the app is doing. 3:31 They're probably safe to omit from the log in most cases. 3:35 Warn messages indicate a potential problem. 3:38 They should probably be included in the log. 3:41 Error messages are definitely a problem and 3:43 should be included in the log no matter what. 3:46 And fatal messages indicate a problem so 3:48 serious that the app is probably about to shut down. 3:50 Okay, so we need to use a log message to look at the contents of params[:pet]. 3:54 Since Rails apps turn debug messages off by default, even in development mode, 3:59 we're going to call the info method to add a message to the log. 4:03 So we'll add some code right before the line where the error occurs. 4:07 We'll call logger to get the logger object. 4:10 I'll call the info method on it and I'll pass a string to it. 4:15 The :pet parameter is, and 4:20 I'll interpolate some Ruby code into the string, 4:22 #{params}, close the interpretation, 4:28 close the string out, and end the method call. 4:32 Let's save that. 4:38 And now let's refresh our browser page so 4:39 that it runs the pets controller edit method again. 4:41 That will run the code that calls logger.info. 4:45 Once that's done, scroll back through your log and you'll see your message. 4:47 The pet parameter is nothing? 4:52 That can't be right. 4:55 We need to figure out what's going on. 4:56 If you look at the log right before our log message, you'll see these messages. 4:58 That's the GET request our browser made to load the edit form. 5:03 See the parameters line there? 5:07 That shows the contents of the params hash. 5:09 We see an id key, but no pet key. 5:11 Aha, there's our problem. 5:15 We were supposed to use params ID when calling pet.find, not params pet. 5:17 So let's go back into the pets controller and fix that. 5:25 We'll remove the log message, save our work, and reload the page. 5:29 Now that we're using a parameter that actually exists, 5:34 the pet record is found successfully and the error is gone. 5:37 The Rails logger can be a useful tool for 5:40 debugging your apps in other situations, too. 5:42 See the teacher's notes if you'd like more info on it. 5:45