Mistakes in Code

Syntax errors are often the easiest problems to find and fix. 0:00 Suppose that we get this error when loading the list of pets. 0:04 We see SyntaxError in PetsController#index. 0:07 We get a file name and a line number, and we see syntax error, unexpected '>'. 0:11 The error points us directly to the file and line number where the problem is, 0:18 line one of app/models/pet.rb. 0:22 In this case, 0:25 we even get a hint as to the nature of the problem, unexpected greater than sign. 0:26 Let's do a web search to figure out what went wrong. 0:31 This line is the start of a class definition, so we'll search for Ruby class 0:34 definition. 0:39 Skimming the results, we see one that talks about using a less than symbol. 0:43 That looks interesting, so let's check that out. 0:48 If we scroll down, we see a section on class inheritance. 0:51 That's relevant to us because our model class inherits from Application Record. 0:55 And in their sample code, it looks like they're using a less than symbol to 0:59 indicate a subclass, not a greater than symbol. 1:03 So the error is that we're supposed to use a less than symbol to indicate that Pet is 1:06 a subclass of ActiveRecord Base, not a greater than symbol. 1:10 Let's try changing that, save our work, and reload our page. 1:14 It looks like everything works again. 1:21 Let's look at another common mistake in code. 1:24 Sometimes Ruby will indicate the error occurred on one line but 1:27 the real problem is elsewhere in the file. 1:29 Suppose we get this error when loading the pets index. 1:32 Syntax error in PetsController#index. 1:35 It indicates a problem on the pets_controller.rb file line 56. 1:38 Let's open that file and line number and see if we can figure out what's going on. 1:43 So app/controllers/pets_controller, and we'll scroll down to line 56. 1:49 We don't really see a problem here, line 56 is just the end of the file. 1:56 But if we scroll higher in the file, suppose we see this. 2:01 See something odd there? 2:05 There's no end keyword at the end of the new definition. 2:07 So Ruby thinks that all the remaining code in the file is part of the new method. 2:10 An error doesn't get reported until the end of the file 2:14 when Ruby fails to find the expected number of end keywords. 2:18 So let's add that end keyword back in, save and reload and our problem is fixed. 2:22 So while Ruby and Rails try to guide you directly to the line with the problem, 2:30 sometimes that isn't possible. 2:34 If this happens, be prepared to widen your search a little bit. 2:36 There's one more common issue I'd like to show you. 2:41 Sometimes typos in your code cause syntax errors and sometimes they cause undefined 2:43 variable or undefined method errors, but you fix them in much the same way. 2:47 Suppose we're trying to load the show view for an individual pet, 2:52 but we're getting this error. 2:55 It says, NameError in Pets#show and it's showing an error in 2:58 the show.html.erb template, undefined local variable or method pet. 3:03 Here's a potentially helpful error message. 3:10 Did you mean @pet, the instance variable? 3:12 The problem is that we forgot the at symbol character at the start of the pet 3:16 instance variable name. 3:20 So Ruby thinks we're trying to access a local variable named pet 3:21 rather than an instance variable named @pet. 3:25 So if we open up app/views/pets/show.html.erb, 3:30 and there on line five, you see the misnamed variable. 3:36 If we add an at symbol, save our work, and reload, 3:41 everything works. 3:45 Thus far, we've focused on fixing error messages, but 3:49 what happens when your site just doesn't look right and 3:52 there's no error message to tell you where the problem is? 3:54 We'll look at that in the next video. 3:57