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Syntax errors are often the easiest
problems to find and fix.

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Suppose that we get this error
when loading the list of pets.

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We see SyntaxError in
PetsController#index.

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We get a file name and a line number,
and we see syntax error, unexpected '>'.

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The error points us directly to the file
and line number where the problem is,

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line one of app/models/pet.rb.

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In this case,

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we even get a hint as to the nature of
the problem, unexpected greater than sign.

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Let's do a web search to
figure out what went wrong.

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This line is the start of a class
definition, so we'll search for Ruby class

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definition.

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Skimming the results, we see one that
talks about using a less than symbol.

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That looks interesting,
so let's check that out.

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If we scroll down,
we see a section on class inheritance.

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That's relevant to us because our model
class inherits from Application Record.

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And in their sample code, it looks like
they're using a less than symbol to

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indicate a subclass,
not a greater than symbol.

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So the error is that we're supposed to use
a less than symbol to indicate that Pet is

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a subclass of ActiveRecord Base,
not a greater than symbol.

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Let's try changing that,
save our work, and reload our page.

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It looks like everything works again.

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Let's look at another
common mistake in code.

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Sometimes Ruby will indicate
the error occurred on one line but

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the real problem is elsewhere in the file.

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Suppose we get this error
when loading the pets index.

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Syntax error in PetsController#index.

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It indicates a problem on
the pets_controller.rb file line 56.

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Let's open that file and line number and
see if we can figure out what's going on.

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So app/controllers/pets_controller,
and we'll scroll down to line 56.

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We don't really see a problem here,
line 56 is just the end of the file.

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But if we scroll higher in the file,
suppose we see this.

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See something odd there?

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There's no end keyword at
the end of the new definition.

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So Ruby thinks that all the remaining code
in the file is part of the new method.

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An error doesn't get reported
until the end of the file

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when Ruby fails to find the expected
number of end keywords.

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So let's add that end keyword back in,
save and reload and our problem is fixed.

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So while Ruby and Rails try to guide you
directly to the line with the problem,

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sometimes that isn't possible.

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If this happens, be prepared to
widen your search a little bit.

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There's one more common
issue I'd like to show you.

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Sometimes typos in your code cause syntax
errors and sometimes they cause undefined

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variable or undefined method errors,
but you fix them in much the same way.

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Suppose we're trying to load
the show view for an individual pet,

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but we're getting this error.

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It says, NameError in Pets#show and
it's showing an error in

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the show.html.erb template,
undefined local variable or method pet.

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Here's a potentially
helpful error message.

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Did you mean @pet, the instance variable?

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The problem is that we forgot the at
symbol character at the start of the pet

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instance variable name.

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So Ruby thinks we're trying to
access a local variable named pet

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rather than an instance
variable named @pet.

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So if we open up
app/views/pets/show.html.erb,

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and there on line five,
you see the misnamed variable.

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If we add an at symbol,
save our work, and reload,

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everything works.

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Thus far, we've focused on
fixing error messages, but

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what happens when your site
just doesn't look right and

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there's no error message to
tell you where the problem is?

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We'll look at that in the next video.