Django Model Error Handling
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Django raises some of its own exceptions as python error handling well as standard Python exceptions. Django Core Exceptions¶
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Django core exception classes are defined in django.core.exceptions. AppRegistryNotReady¶ exception AppRegistryNotReady[source]¶ python error handling loop This exception is raised when attempting to use models before the app loading process, which initializes the ORM, is complete. ObjectDoesNotExist¶ exception ObjectDoesNotExist[source]¶ The base class for DoesNotExist exceptions; a try/except for ObjectDoesNotExist will catch DoesNotExist exceptions for all models. See get() for further information on ObjectDoesNotExist and DoesNotExist. FieldDoesNotExist¶ exception FieldDoesNotExist[source]¶ The class="pre">FieldDoesNotExistRuby Error Handling
A view function, or view for short, is simply a Python function that takes a Web request and returns a Web response. This response can be php error handling the HTML contents of a Web page, or a redirect, or a c++ error handling 404 error, or an XML document, or an image . . . or anything, really. The view itself
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contains whatever arbitrary logic is necessary to return that response. This code can live anywhere you want, as long as it's on your Python path. There's no other requirement-no "magic," https://docs.djangoproject.com/en/1.10/ref/exceptions/ so to speak. For the sake of putting the code somewhere, the convention is to put views in a file called views.py, placed in your project or application directory. A simple view¶ Here's a view that returns the current date and time, as an HTML document: from django.http import HttpResponse import datetime def current_datetime(request): now = datetime.datetime.now() html = https://docs.djangoproject.com/en/1.10/topics/http/views/ "
It is now %s." % now return HttpResponse(html) Let's step through this code one line at a time: First, we import the class HttpResponse from the django.http module, along with Python's datetime library. Next, we define a function called current_datetime. This is the view function. Each view function takes an HttpRequest object as its first parameter, which is typically named request. Note that the name of the view function doesn't matter; it doesn't have to be named in a certain way in order for Django to recognize it. We're calling it current_datetime here, because that name clearly indicates what it does. The view returns an HttpResponse object that contains the generated response. Each view function is responsible for returning an HttpResponse object. (There are exceptions, but we'll get to those later.) Django's Time Zone Django includes a TIME_ZONE setting that defaults to America/Chicago. This probably isn't where you live, so you might want to change it in your settings file. Mapping URLs to views¶ So, to recap,validation¶ Form validation happens when the data is cleaned. If you want to customize this process, there are various places to make changes, each one serving a https://docs.djangoproject.com/en/1.10/ref/forms/validation/ different purpose. Three types of cleaning methods are run during form processing. http://www.django-rest-framework.org/api-guide/exceptions/ These are normally executed when you call the is_valid() method on a form. There are other things that can also trigger cleaning and validation (accessing the errors attribute or calling full_clean() directly), but normally they won't be needed. In general, any cleaning method can raise ValidationError error handling if there is a problem with the data it is processing, passing the relevant information to the ValidationError constructor. See below for the best practice in raising ValidationError. If no ValidationError is raised, the method should return the cleaned (normalized) data as a Python object. Most validation can be done using validators - simple helpers that can be reused python error handling easily. Validators are simple functions (or callables) that take a single argument and raise ValidationError on invalid input. Validators are run after the field's to_python and validate methods have been called. Validation of a form is split into several steps, which can be customized or overridden: The to_python() method on a Field is the first step in every validation. It coerces the value to a correct datatype and raises ValidationError if that is not possible. This method accepts the raw value from the widget and returns the converted value. For example, a FloatField will turn the data into a Python float or raise a ValidationError. The validate() method on a Field handles field-specific validation that is not suitable for a validator. It takes a value that has been coerced to a correct datatype and raises ValidationError on any error. This method does not return anything and shouldn't alter the value. You should override it to handle validation logic that you can't or don't want to put in a validator. The