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Good, the form won’t allow you to save if you give it an empty item text.
Now let’s see if we can get it to use the specific error message that we want. The API for
checking form validation
before
we try and save any data is a function called
is_valid
:
lists/tests/test_forms.py (ch11l009).
def
test_form_validation_for_blank_items
(
self
):
form
=
ItemForm
(
data
=
{
'text'
:
''
})
self
.
assertFalse
(
form
.
is_valid
())
self
.
assertEqual
(
form
.
errors
[
'text'
],
[
"You can't have an empty list item"
]
)
Calling
form.is_valid()
returns
True
or
False
, but it also has the side effect of vali‐
dating the input data, and populating the
errors
attribute. It’s a dictionary mapping the
names of fields to lists of errors for those fields (it’s possible for a field to have more than
one error).
That gives us:
AssertionError: ['This field is required.'] != ["You can't have an empty list
item"]
Django already has a default error message that we could present to the user—youmight
use it if you were in a hurry to build your web app, but we care enough to make our
message special. Customising it means changing
error_messages
, another
Meta
variable:
lists/forms.py (ch11l010).
class
Meta
:
model
=
Item
fields
=
(
'text'
,)
widgets
=
{
'text'
:
forms
.
fields
.
TextInput
(
attrs
=
{
'placeholder'
:
'Enter a to-do item'
,
'class'
:
'form-control input-lg'
,
}),
}
error_messages
=
{
'text'
: {
'required'
:
"You can't have an empty list item"
}
}
OK
You know what would be even better than messing about with all these error strings?
Having a constant:
lists/forms.py (ch11l011).
EMPTY_LIST_ERROR
=
"You can't have an empty list item"
[
...
]
error_messages
=
{
Moving Validation Logic into a Form
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