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Updating Partials
3:31"Partial" is short for "partial view". And it's a partial that contains the HTML code for the form.
So in both our edit and
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new templates, we see a call to the render
method with an argument of form.
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When render is called from either of
these templates, it looks up a partial.
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Partial is short for PartialView and
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it's this partial contains
the HTML code for the form.
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When you need an element to look identical
on multiple pages in your app, it's a pain
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to maintain multiple copies of that
element within multiple erb templates.
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Any time you change one,
you have to remember to change the other.
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Otherwise, they could get out of sync and
might wind up looking different or
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one of them could stop working altogether.
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And that's why Rails offers partials.
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You can take the HTML code that's
identical between the templates and
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move it to a partial view.
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Then, each template that needs that
code can render the partial and
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the partial's code will be
included in the template's code.
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When you need to make a change,
you only have to update the partial.
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Any changes you make will immediately
be visible in all the views that
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use that partial.
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So both the Edit Post page and
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the New Post page include a call
to render a partial called form.
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If we look at the log,
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we'll see it's been showing us the step
where it renders the partial all along.
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Within both the edit and new requests,
we'll see rendered posts/_form.html.erb.
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The underscore at the start of
the filename indicates that a file
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holds a partial template.
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When calling render, you can leave the
underscore and the html.erb extension off.
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Rails adds those automatically,
that just leaves render form.
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Following the name of the partial is
a hash that sets up local variables for
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use within the partial.
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So this will make the object referenced
by the post instance variable
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available within the partial
under the post local variable.
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Let's open the partial file
to see what it contains.
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It's at app > views >
posts > _form.html.erb.
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We can see that it takes
the post object we passed in and
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renders an HTML form for it.
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The f block parameter here will hold the
Ruby object representing the HTML form.
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We can call methods on that object
to add elements to the HTML form.
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We can see the code for
the title field here.
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Let's mimic that for the body field.
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So we'll copy it and paste.
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We'll create another div
with class of field.
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We'll set up an HTML label for
the body field.
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Just like the one for the title by calling
the label method on the form object and
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passing it a parameter of body.
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Then we'll set up a field for
the body, but
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instead of calling the text field
method we'll call the text area method.
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This will give the user
a larger area to type in.
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And we'll change the title
argument to body.
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If we save our work,
go back to our browser and
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refresh our page, we'll see a new
form where we can enter a post body.
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And if we go to the Edit page,
we'll see a field there as well.
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But there's a problem.
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On our New Post form,
if we fill up the post body and submit it,
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We'll see that the body
field is still blank.
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To fix that, we're going to have to make
one last change in our controller code.
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We'll look at how to do that next.
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