Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
Validators, whether custom or Django-provided, give us a great way to make sure the content of a field matches a condition we've set.
Did you notice my flip-flop in the video? Writing a custom validator is a great way to have reusable validation, so if I need to do something specific on a lot of fields, I definitely use a custom validator. In the example in this video, though, it just makes more sense to use Django's provided MaxLengthValidator. Sorry if that was a bit confusing!
Django provides us with several validators
already built in, so that we don't have to
0:00
handle things like checking for a maximum
or minimum value, max or min length, or
0:03
a valid email or IP address, but our honey
pot needs to be validated to be blank.
0:08
We're already doing this with
our clean honey pot method,
0:14
but that's not easily reusable, so
we should come up with something else.
0:16
Let's do this two ways.
0:20
The max length validator,
and with a custom validator.
0:22
So we have this easy way of
cleaning our honeypot, and
0:26
this is really good, but
it's not something that is abstracted,
0:29
it's not something that we can apply
to a bunch of different forms.
0:33
We could turn it into that, but
0:37
that's probably more trouble
than it's really worth.
0:39
And we don't wanna have to write
this method every single time
0:41
we use a honeypot.
0:44
We'd probably end up just copying and
pasting it over, and over, and over again.
0:44
That's not the best idea,
so what can we do instead?
0:49
Well, what we can do is we
can bring in a core Django
0:53
feature called validators that
validate data, so let's do that.
0:56
Let's get rid of our clean honeypot.
1:02
And let's come up here, and we want to
do from django.core import validators.
1:05
So that just gives us
all of our validators.
1:13
And here on our honeypot, we want
to specify what the validators are.
1:16
So we can do validators=, and
1:21
we can put in
validators.MaxLengthValidator.
1:25
And the max length is 0.
1:32
Length of zero, if there's any
length at all, then this fails.
1:37
All right so let's come back over here and
we can actually we've already got this set
1:42
up with the bad value, so
let's just hit submit.
1:47
We should see another error
message come out right up here.
1:49
Yep, so here we go hidden field honey
pot ensure this value has at most
1:53
zero characters, it has seven.
1:57
So, great.
2:00
That's actually pretty simple.
2:01
And this actually works really well.
2:03
I like this.
2:05
This is probably how I would
handle this situation.
2:06
Just give it this MaxLengthValidator of 0.
2:09
But sometimes you need something that's
a little more complicated of a validation.
2:11
So let's see how to write
a custom validator.
2:16
So we're just gonna come up here and
we're gonna make a new function.
2:20
And I'm just gonna say must be empty.
2:24
And validators always get a value.
2:29
They get the value that's in
the field that they're validating.
2:30
So we'll just call that value and
we'll say if value.
2:34
If there's anything there at all.
2:37
If there's a value.
2:39
Then we want to raise
forms.validationError.
2:41
And we're gonna say is not empty,
2:50
because really you're reflecting
what the state of the field is.
2:52
So the state of the field is
that the field isn't empty, and
2:57
that field should be empty.
3:00
So then in here,
inside of the MaxLengthValidator,
3:01
we'll just put must_be_empty.
3:04
And then we'll come over here.
3:09
Everything is still filled in.
3:11
And if we submit this,
we should see something new there.
3:12
And there we go,
we have honeypot is not empty.
3:16
So three different ways to handle
cleaning out that one field.
3:19
They all have their own strengths and
weaknesses.
3:23
I'll leave it to you to decide which
one of those solutions is better.
3:26
They both have pros and cons, but
3:29
I tend to like the CustomValidator a bit
better because it's a bit more explicit.
3:30
Anyone applying that to their form
fields will know exactly what it's for.
3:35
You need to sign up for Treehouse in order to download course files.
Sign up