Filosofía de diseño¶
This document explains some of the fundamental philosophies Django’s developers have used in creating the framework. Its goal is to explain the past and guide the future.
En general¶
Bajo acoplamiento¶
A fundamental goal of Django’s stack is loose coupling and tight cohesion. The various layers of the framework shouldn’t «know» about each other unless absolutely necessary.
For example, the template system knows nothing about web requests, the database layer knows nothing about data display and the view system doesn’t care which template system a programmer uses.
Although Django comes with a full stack for convenience, the pieces of the stack are independent of another wherever possible.
Menos código¶
Django apps should use as little code as possible; they should lack boilerplate. Django should take full advantage of Python’s dynamic capabilities, such as introspection.
Desarrollo rápido¶
The point of a web framework in the 21st century is to make the tedious aspects of web development fast. Django should allow for incredibly quick web development.
No te repitas (NTR)¶
Cada concepto distinto y/o dato debe ubicarse en un y sólo un lugar. La redundancia es mala. La normalización es buena.
The framework, within reason, should deduce as much as possible from as little as possible.
Explícito es mejor que implícito¶
This is a core Python principle listed in PEP 20, and it means Django shouldn’t do too much «magic.» Magic shouldn’t happen unless there’s a really good reason for it. Magic is worth using only if it creates a huge convenience unattainable in other ways, and it isn’t implemented in a way that confuses developers who are trying to learn how to use the feature.
Consistencia¶
The framework should be consistent at all levels. Consistency applies to everything from low-level (the Python coding style used) to high-level (the «experience» of using Django).
Modelos¶
Explícito es mejor que implícito¶
Fields shouldn’t assume certain behaviors based solely on the name of the field. This requires too much knowledge of the system and is prone to errors. Instead, behaviors should be based on keyword arguments and, in some cases, on the type of the field.
Incluya toda la lógica de dominio relevante¶
Los modelos deberían encapsular todos los aspectos de un «objeto», siguiendo el patrón de diseño ActiveRecord de Martin Fowler.
This is why both the data represented by a model and information about it (its human-readable name, options like default ordering, etc.) are defined in the model class; all the information needed to understand a given model should be stored in the model.
API de base de datos¶
Los objetivos principales de la API de base de datos son:
La eficiencia de SQL¶
It should execute SQL statements as few times as possible, and it should optimize statements internally.
This is why developers need to call save() explicitly, rather than the
framework saving things behind the scenes silently.
This is also why the select_related() QuerySet method exists. It’s an
optional performance booster for the common case of selecting «every related
object.»
Sintaxis concisa y potente¶
The database API should allow rich, expressive statements in as little syntax as possible. It should not rely on importing other modules or helper objects.
Joins should be performed automatically, behind the scenes, when necessary.
Every object should be able to access every related object, systemwide. This access should work both ways.
Option to drop into raw SQL easily, when needed¶
The database API should realize it’s a shortcut but not necessarily an
end-all-be-all. The framework should make it easy to write custom SQL – entire
statements, or just custom WHERE clauses as custom parameters to API calls.
Diseño de URLs¶
Bajo acoplamiento¶
URLs in a Django app should not be coupled to the underlying Python code. Tying URLs to Python function names is a Bad And Ugly Thing.
Along these lines, the Django URL system should allow URLs for the same app to
be different in different contexts. For example, one site may put stories at
/stories/, while another may use /news/.
Flexibilidad infinita¶
URLs should be as flexible as possible. Any conceivable URL design should be allowed.
Fomente las buenas prácticas¶
The framework should make it just as easy (or even easier) for a developer to design pretty URLs than ugly ones.
File extensions in web-page URLs should be avoided.
Vignette-style commas in URLs deserve severe punishment.
URLs definitivas¶
Technically, foo.com/bar and foo.com/bar/ are two different URLs, and
search-engine robots (and some web traffic-analyzing tools) would treat them as
separate pages. Django should make an effort to «normalize» URLs so that
search-engine robots don’t get confused.
Este es el razonamiento detrás de la opción :setting: APPEND_SLASH.
Sistema de plantillas¶
Separe la lógica de la presentación¶
We see a template system as a tool that controls presentation and presentation-related logic – and that’s it. The template system shouldn’t support functionality that goes beyond this basic goal.
No promueva la redundancia¶
The majority of dynamic websites use some sort of common sitewide design – a common header, footer, navigation bar, etc. The Django template system should make it easy to store those elements in a single place, eliminating duplicate code.
This is the philosophy behind template inheritance.
Be decoupled from HTML¶
The template system shouldn’t be designed so that it only outputs HTML. It should be equally good at generating other text-based formats, or just plain text.
XML no se debe utilizar para los lenguajes de plantillas¶
Using an XML engine to parse templates introduces a whole new world of human error in editing templates – and incurs an unacceptable level of overhead in template processing.
Adopte las competencias de diseñador¶
The template system shouldn’t be designed so that templates necessarily are displayed nicely in WYSIWYG editors such as Dreamweaver. That is too severe of a limitation and wouldn’t allow the syntax to be as nice as it is. Django expects template authors are comfortable editing HTML directly.
Treat whitespace obviously¶
The template system shouldn’t do magic things with whitespace. If a template includes whitespace, the system should treat the whitespace as it treats text – just display it. Any whitespace that’s not in a template tag should be displayed.
No invente un lenguaje de programación¶
The goal is not to invent a programming language. The goal is to offer just enough programming-esque functionality, such as branching and looping, that is essential for making presentation-related decisions. The Django Template Language (DTL) aims to avoid advanced logic.
Seguridad y protección¶
The template system, out of the box, should forbid the inclusion of malicious code – such as commands that delete database records.
Esta es otra razón por la que el sistema de plantillas no permite código Python arbitrario.
Extensibilidad¶
The template system should recognize that advanced template authors may want to extend its technology.
Esta es la filosofía detrás de las etiquetas de plantillas y filtros personalizados.
Vistas¶
Sencillez¶
Writing a view should be as simple as writing a Python function. Developers shouldn’t have to instantiate a class when a function will do.
Utilice objetos de petición¶
Views should have access to a request object – an object that stores metadata about the current request. The object should be passed directly to a view function, rather than the view function having to access the request data from a global variable. This makes it light, clean and easy to test views by passing in «fake» request objects.
Bajo acoplamiento¶
A view shouldn’t care about which template system the developer uses – or even whether a template system is used at all.
Diferencie entre GET y POST¶
GET and POST are distinct; developers should explicitly use one or the other. The framework should make it easy to distinguish between GET and POST data.
Framework caché¶
Los objetivos centrales del :doc: framework caché de Django </topics/cache> son:
Menos código¶
A cache should be as fast as possible. Hence, all framework code surrounding
the cache backend should be kept to the absolute minimum, especially for
get() operations.
Consistencia¶
The cache API should provide a consistent interface across the different cache backends.
Extensibilidad¶
The cache API should be extensible at the application level based on the developer’s needs (for example, see Cache key transformation).
