Develop Reference

Possibility of having variable parameter names in Django model updates

I'd like to shorten the following code from
if field == 'favorite_food':
model_instance.update(favorite_food=value)
elif field == 'favorite_drink':
model_instance.update(favorite_drink=value)
elif field == 'favorite_color':
model_instance.update(favorite_color=value)
to something like:
if field in list:
model_instance.update(field=value)
So I'm just wondering if it's possible.

You can just unpack into keyword arguments:
model_instance.update(**{field: value})
There is also an option to set the model field value and then save (there are though differences):
setattr(model_instance, field, value)
model_instance.save()

You can do this
fields = ["favorite_food", "favorite_drink", "favorite_color"]
field = "favorite_food"
if field in fields:
model_instance.update(field=value)

How to compute a databasefield with the field-id

Model:
db.define_table('orders',
Field('customer_id', db.customer)
Field('order_id', 'string')
)
I want to get a special order_id like XY-150012 where XY is part of the customer name, 15 is the year and 12 the id the actual record-id of orders. I tried in the model:
db.orders.order_id.compute = lambda r: "%s-%s00%s" % (db.customer(r['customer_id']).short, str(request.now.year)[2:], r['id'])
The id is never recognized, the computation ends up as None. If I remove r['id'] from the compute-line it works.
EDIT:
After adding an extra field field('running_number', 'integer') to the model I can access this fields content.
Is there a easy way to set this fields default=db.orders.id?
SOLUTION:
With Anthony´s Input, and reading about recursive selects I came up with this solution:
db.define_table('orders',
Field('customer_id', db.customer),
Field('order_id', 'string', default = None))
def get_order_id(id, short):
y = str(request.now.year)[2:]
return '%s-%s00%s' % (short, y, id)
def set_id_after_insert(fields,id):
fields.update(id=id)
def set_order_id_after_update(s,f):
row = s.select().first()
if row['order_id'] == None:
s.update_naive(order_id=get_order_id(row['id'], row['customer_id'].short)
else:
return
db.orders._after_insert.append(lambda f,id: set_id_after_insert(f,id))
db.orders._after_update.append(lambda s,f: set_order_id_after_update(s,f))

The problem is that the record ID is not known until after the record has been inserted in the database, as the id field is an auto-incrementing integer field whose value is generated by the database, not by web2py.
One option would be to define an _after_insert callback that updates the order_id field after the insert:
def order_after_insert(fields, id):
fields.update(id=id)
db(db.order.id == id).update(order_id=db.order.order_id.compute(fields))
db.order._after_insert.append(order_after_insert)
You might also want to create an _after_update callback, but in that case, be sure to use the update_naive argument in both callbacks when defining the Set (see above link for details).
Depending on how the order_id is used, another option might be a virtual field.

iterate over django form results (not in a template)

I am trying to iterate over form results and I can't help but think that I am re-inventing the wheel here.
filterlist = []
if request.POST:
form = FilterForm(request.POST)
if form.is_valid():
for key, value in form.cleaned_data.iteritems():
filterlist.append(key)
filterlist.append(value)
This works, but seems very awkward and creates lots of other problems. For example the values come back with u' so I have to use value.encode("utf8") but then if a value is None it throws in error. So now I have to check if it is None, if not then encode. There has to be a better way.
EDIT: What I am trying to do.
I am trying to filter what is shown on a page. The problem I am running into is that if a value is empty (the user don't fill the box because they only want to filter against one object) then I get no results. For example a user wants to search for all books by the author name "Smith" but doesn't want to search against a genre.
results = Books.objects.filter(author=author, genre=genre)
The user would get no results because this is an AND search. But, if a user put in "Smith" for the author and "mystery" for the genre then it works exactly like I want it to, only giving results where both are true.
So, I am trying to eliminate the empty stuff by iterating over the form results. Like I said I am probably re-inventing the wheel here.

In Python 3 use:
for key, value in form.cleaned_data.items():

If the field names are the same in the model and the form, try this:
filter = {}
if request.method == 'POST':
form = FilterForm(request.POST)
if form.is_valid():
for key, value in form.cleaned_data.iteritems():
if value:
filter[key] = value
results = Books.objects.filter(**filter)
Python is one of the few languages having named parameters. You can assemble a dict with the non-empty form fields and pass it to the filter method using the kwargs unpacking operator **.
For example:
kwargs = {"author": "Freud"}
results = Books.objects.filter(**kwargs)
Is the same as:
results = Books.objects.filter(author="Freud")

I think the problem is that by default the Model form is not valid if a form field does not have a value entered by the user, if you don`t require the field every time from the user you need to set the required field to false in the ModelForm class in forms.py as shown in the code below. Remember that the field is set false only in the model form not in the model itself
class myForm(forms.ModelForm):
myfield_id = forms.CharField(required=False)
myfield_foo = forms.CharField(required=False)
myfield_bar = forms.CharField(required=False)
myfield_name = forms.CharField(required=False)
class Meta:
model = myModel
exclude = ('myfield_ex','myfield_file')
fields = ['myfield_id','myfield_foo','myfield_bar','myfield_name',]
After you have the form entered by the user what you need is use the Q object which can be used to create complex queries as described in the manula page here
https://docs.djangoproject.com/en/1.7/topics/db/queries/#complex-lookups-with-q
A simple example code would look like
if form.is_valid():
qgroup = []
for key,value in form.cleaned_data.iteritems():
if value:
q_name = Q(**{"%s"%format(filterKey[key]) : value})
qgroup.append(q_name)
q = None
# can use the reduce as shown here qgroup = reduce(operator.or_, (Q(**{"{0}".format(filterKey[key]): value}) for (key,value) in form.cleaned_data.iteritems()))
for key,value in form.cleaned_data.iteritems():
if value:
q_name = Q(**{"%s"%format(filterKey[key]) : value})
qgroup.append(q_name)
for x in qgroup:
q &= x ### Or use the OR operator or
if q:
resultL = myModel.objects.filter(q).select_related()
The filterKey can look something on the lines of
filterKey = {'myfield_id' : "myfield_id",
'myfield_foo' : "myfield_foo__icontains",
'myfield_bar' : "myfield_bar__relative_field__icontains",
}

How to initialize django-form data type field from a given choices?

First of all: I am not able to find out the proper Title of this question.
Anyhow the question is:
I have to fill a form at template and the fields of this form are user dependent. For example you passes integer (integer is not a datatype) as a parameter to the method and it should returns like this:
fileds = forms.IntegerField()
If you pass bool then it should like this:
fields = forms.BooleanField()
So that i can use them to create my form. I tried with this code but it returns into the form of string.
Some.py file:
choices = (('bool','BooleanField()'),
('integer','IntegerField()'))
def choose_field():
option = 'bool' # Here it is hardcoded but in my app it comes from database.
for x in choices:
if x[0]==option:
type = x[1]
a = 'forms'
field = [a,type]
field = ".".join(field)
return field
When i print the field it prints 'forms.BooleanField()'. I also use this return value but it didn't work. Amy solution to this problem?

The simpliest way is to create your form class and include fields for all possible choices to it. Then write a constructor in this class and hide the fields you don't want to appear. The constructor must take a parameter indicating which fields do we need. It can be useful to store this parameter in the form and use it in clean method to correct collected data accordingly to this parameter.
class Your_form(forms.ModelForm):
field_integer = forms.IntegerField()
field_boolean = forms.BooleanField()
def __init__(self, *args, **kwargs):
option = kwargs["option"]
if option == "integer":
field_boolean.widget = field_boolean.hidden_widget()
else:
field_integer.widget = field_integer.hidden_widget()
super(Your_form, self).__init__(*args, **kwargs)
In your controller:
option = 'bool'
form = Your_form(option=option)

How would you inherit from and override the django model classes to create a listOfStringsField?

I want to create a new type of field for django models that is basically a ListOfStrings. So in your model code you would have the following:
models.py:
from django.db import models
class ListOfStringsField(???):
???
class myDjangoModelClass():
myName = models.CharField(max_length=64)
myFriends = ListOfStringsField() #
other.py:
myclass = myDjangoModelClass()
myclass.myName = "bob"
myclass.myFriends = ["me", "myself", "and I"]
myclass.save()
id = myclass.id
loadedmyclass = myDjangoModelClass.objects.filter(id__exact=id)
myFriendsList = loadedclass.myFriends
# myFriendsList is a list and should equal ["me", "myself", "and I"]
How would you go about writing this field type, with the following stipulations?
We don't want to do create a field which just crams all the strings together and separates them with a token in one field like this. It is a good solution in some cases, but we want to keep the string data normalized so tools other than django can query the data.
The field should automatically create any secondary tables needed to store the string data.
The secondary table should ideally have only one copy of each unique string. This is optional, but would be nice to have.
Looking in the Django code it looks like I would want to do something similar to what ForeignKey is doing, but the documentation is sparse.
This leads to the following questions:
Can this be done?
Has it been done (and if so where)?
Is there any documentation on Django about how to extend and override their model classes, specifically their relationship classes? I have not seen a lot of documentation on that aspect of their code, but there is this.
This is comes from this question.

There's some very good documentation on creating custom fields here.
However, I think you're overthinking this. It sounds like you actually just want a standard foreign key, but with the additional ability to retrieve all the elements as a single list. So the easiest thing would be to just use a ForeignKey, and define a get_myfield_as_list method on the model:
class Friends(model.Model):
name = models.CharField(max_length=100)
my_items = models.ForeignKey(MyModel)
class MyModel(models.Model):
...
def get_my_friends_as_list(self):
return ', '.join(self.friends_set.values_list('name', flat=True))
Now calling get_my_friends_as_list() on an instance of MyModel will return you a list of strings, as required.

What you have described sounds to me really similar to the tags.
So, why not using django tagging?
It works like a charm, you can install it independently from your application and its API is quite easy to use.

I also think you're going about this the wrong way. Trying to make a Django field create an ancillary database table is almost certainly the wrong approach. It would be very difficult to do, and would likely confuse third party developers if you are trying to make your solution generally useful.
If you're trying to store a denormalized blob of data in a single column, I'd take an approach similar to the one you linked to, serializing the Python data structure and storing it in a TextField. If you want tools other than Django to be able to operate on the data then you can serialize to JSON (or some other format that has wide language support):
from django.db import models
from django.utils import simplejson
class JSONDataField(models.TextField):
__metaclass__ = models.SubfieldBase
def to_python(self, value):
if value is None:
return None
if not isinstance(value, basestring):
return value
return simplejson.loads(value)
def get_db_prep_save(self, value):
if value is None:
return None
return simplejson.dumps(value)
If you just want a django Manager-like descriptor that lets you operate on a list of strings associated with a model then you can manually create a join table and use a descriptor to manage the relationship. It's not exactly what you need, but this code should get you started.

Thanks for all those that answered. Even if I didn't use your answer directly the examples and links got me going in the right direction.
I am not sure if this is production ready, but it appears to be working in all my tests so far.
class ListValueDescriptor(object):
def __init__(self, lvd_parent, lvd_model_name, lvd_value_type, lvd_unique, **kwargs):
"""
This descriptor object acts like a django field, but it will accept
a list of values, instead a single value.
For example:
# define our model
class Person(models.Model):
name = models.CharField(max_length=120)
friends = ListValueDescriptor("Person", "Friend", "CharField", True, max_length=120)
# Later in the code we can do this
p = Person("John")
p.save() # we have to have an id
p.friends = ["Jerry", "Jimmy", "Jamail"]
...
p = Person.objects.get(name="John")
friends = p.friends
# and now friends is a list.
lvd_parent - The name of our parent class
lvd_model_name - The name of our new model
lvd_value_type - The value type of the value in our new model
This has to be the name of one of the valid django
model field types such as 'CharField', 'FloatField',
or a valid custom field name.
lvd_unique - Set this to true if you want the values in the list to
be unique in the table they are stored in. For
example if you are storing a list of strings and
the strings are always "foo", "bar", and "baz", your
data table would only have those three strings listed in
it in the database.
kwargs - These are passed to the value field.
"""
self.related_set_name = lvd_model_name.lower() + "_set"
self.model_name = lvd_model_name
self.parent = lvd_parent
self.unique = lvd_unique
# only set this to true if they have not already set it.
# this helps speed up the searchs when unique is true.
kwargs['db_index'] = kwargs.get('db_index', True)
filter = ["lvd_parent", "lvd_model_name", "lvd_value_type", "lvd_unique"]
evalStr = """class %s (models.Model):\n""" % (self.model_name)
evalStr += """ value = models.%s(""" % (lvd_value_type)
evalStr += self._params_from_kwargs(filter, **kwargs)
evalStr += ")\n"
if self.unique:
evalStr += """ parent = models.ManyToManyField('%s')\n""" % (self.parent)
else:
evalStr += """ parent = models.ForeignKey('%s')\n""" % (self.parent)
evalStr += "\n"
evalStr += """self.innerClass = %s\n""" % (self.model_name)
print evalStr
exec (evalStr) # build the inner class
def __get__(self, instance, owner):
value_set = instance.__getattribute__(self.related_set_name)
l = []
for x in value_set.all():
l.append(x.value)
return l
def __set__(self, instance, values):
value_set = instance.__getattribute__(self.related_set_name)
for x in values:
value_set.add(self._get_or_create_value(x))
def __delete__(self, instance):
pass # I should probably try and do something here.
def _get_or_create_value(self, x):
if self.unique:
# Try and find an existing value
try:
return self.innerClass.objects.get(value=x)
except django.core.exceptions.ObjectDoesNotExist:
pass
v = self.innerClass(value=x)
v.save() # we have to save to create the id.
return v
def _params_from_kwargs(self, filter, **kwargs):
"""Given a dictionary of arguments, build a string which
represents it as a parameter list, and filter out any
keywords in filter."""
params = ""
for key in kwargs:
if key not in filter:
value = kwargs[key]
params += "%s=%s, " % (key, value.__repr__())
return params[:-2] # chop off the last ', '
class Person(models.Model):
name = models.CharField(max_length=120)
friends = ListValueDescriptor("Person", "Friend", "CharField", True, max_length=120)
Ultimately I think this would still be better if it were pushed deeper into the django code and worked more like the ManyToManyField or the ForeignKey.

I think what you want is a custom model field.