Django Tutorial Walkthrough 4B

This is part 4B (2nd part of part 4) of the code walkthrough of the official Django tutorial. https://docs.djangoproject.com/en/4.0/intro/tutorial04/

Transcript

The following transcript was automatically generated by an algorithm.

00:01 : welcome to part
00:03 : 4b
00:04 : of
00:05 : this code tutorial walkthrough for the
00:09 : django web application framework
00:12 : um
00:14 : we
00:14 : uh we didn't finish
00:16 : uh part four in the last video so we're
00:19 : continuing
00:20 : uh
00:21 : sort of a
00:23 : second part
00:24 : to finish it off and
00:26 : we left off with
00:29 : the generic views section
00:32 : so we're being introduced to the generic
00:35 : views concept
00:37 : in django
00:38 : which um
00:41 : based on what we've read it's it's a way
00:44 : to
00:45 : remove the duplicated code
00:49 : which is
00:50 : common between many of these view
00:52 : functions
00:53 : um and the common pattern is you
00:56 : query you make a database query to get
00:59 : an object
01:02 : and then
01:03 : you
01:04 : take that object pass it on to
01:07 : a template an html template
01:11 : which will then in turn render the page
01:15 : using the objects
01:17 : that that you supply and this pattern
01:20 : because it's so common and you have to
01:22 : write
01:23 : very repetitive code like this
01:26 : they devised a concept called generic
01:29 : views which allows you to write
01:32 : less code to do the same thing so let's
01:34 : see what it looks like
01:38 : um
01:41 : so
01:42 : yeah
01:44 : so we're gonna convert our poll app to
01:48 : use the generic views system so we can
01:51 : delete a bunch of our code we'll have to
01:54 : take a few steps to make the conversion
01:56 : we're going to convert
01:58 : the url conf
02:00 : delete some of the old unneeded unneeded
02:03 : views and introduce some views based on
02:07 : the generic views
02:09 : why the code shuffling generally when
02:12 : writing a django app you evaluate
02:15 : whether generic views are a good fit for
02:17 : your problem
02:18 : and you use them from the beginning
02:21 : rather than refactor you could have
02:24 : refactoring your code halfway through
02:26 : but this tutorial intentionally
02:29 : has focused on writing the views the
02:31 : hard way
02:33 : until now to focus on the core concepts
02:37 : you should know basic math before you
02:39 : start using a calculator
02:41 : i agree with that approach
02:44 : i like knowing the nuts and bolts
02:48 : um
02:50 : because if if you don't know the nuts
02:52 : and bolts and you go directly to the
02:55 : very very convenient way of putting
02:57 : things together then you don't actually
02:59 : know anything
03:01 : about what's happening internally
03:05 : and that means you are not able to
03:07 : troubleshoot things when they do not
03:10 : work anymore
03:12 : okay so first we're gonna amend the url
03:15 : conf which is in the it's the in the
03:19 : urls.py file
03:21 : under the pose
03:23 : subdirectory so it's this one
03:29 : and how are we going to amend it
03:32 : um
03:35 : oh
03:36 : interesting
03:39 : okay
03:40 : whereas before we had views that index
03:44 : now we're changing it to be views dot
03:47 : index view
03:48 : dot as view okay
03:51 : um
03:52 : index view apparently is going to be a
03:54 : class which has not yet been defined but
03:58 : will be defined
04:00 : and we're doing uh the same thing it i
04:03 : believe for um
04:06 : and also we're changing these int colon
04:09 : question id to in colon pk
04:17 : this one is actually stays question id
04:20 : actually for the vote one
04:23 : um that's interesting
04:25 : um uh we're actually not changing the
04:28 : vote one
04:30 : that's interesting to note not changing
04:33 : this one
04:35 : but we're changing the other ones so
04:37 : this detail one
04:39 : which used to be views that detail is
04:42 : getting changed to detail view that as
04:45 : view
04:48 : okay and then this
04:50 : this
04:52 : views that results that will also change
04:55 : to results view that as view
04:59 : okay
05:02 : let's do it like this
05:08 : all right so
05:12 : we need to create these
05:14 : things now i believe so that's
05:17 : where this comes in so now we're gonna
05:19 : open up the views
05:21 : dot pi file
05:23 : and it looks like
05:24 : we're replacing
05:27 : all of these um
05:30 : view functions with exception of this
05:32 : devote method and vote function sorry
05:35 : not method this is just a function
05:38 : we're not changing this one
05:41 : as as we didn't change this this path
05:44 : definition we're also not changing this
05:46 : view function but we're
05:48 : sort of scrapping
05:50 : the other three and replacing them with
05:54 : these
05:55 : generic views
05:57 : which are defined as classes so let's do
06:01 : the first one
06:02 : i'm gonna make a class called index view
06:05 : which
06:06 : extends
06:08 : generic.list view
06:11 : what's a generic well it's comes from
06:13 : the django views so well youtube from
06:18 : views django.views need to import
06:20 : generic
06:26 : and the template name is going to be
06:33 : polls
06:34 : slash index html
06:38 : context object name is going to be
06:41 : latest
06:43 : question
06:45 : list
06:47 : and then
06:48 : get
06:49 : query set
06:52 : is a method that's gonna return question
06:56 : dot objects dot order by
07:02 : this is what we had from before
07:05 : um
07:06 : for this well more or less the first
07:08 : line
07:10 : of the the method we had
07:13 : um maybe i should keep that one
07:17 : just so that we have a before and after
07:20 : comparison so i'm gonna copy this
07:35 : there
07:36 : so this is before
07:40 : and this is after so i'm going to
07:42 : collapse these
07:46 : so
07:46 : this index function is getting replaced
07:50 : by this um
07:52 : index view
07:57 : it seems like we just moved to various
07:59 : elements
08:00 : like this
08:03 : this one here
08:05 : this
08:06 : template name it got moved over here
08:10 : and the context object name that's just
08:14 : this guy it got moved up to here and
08:17 : then this
08:19 : query code got moved to here
08:22 : and now we don't have to explicitly call
08:25 : the render
08:26 : function anymore
08:29 : um
08:31 : yeah that's more or less the difference
08:34 : i would say
08:36 : okay
08:37 : so i'm gonna comment out this one
08:40 : um
08:42 : okay but for a detail view there's even
08:46 : less code here so let's do the detail
08:49 : view
08:51 : class detail
08:53 : view which also extends generic.detail
08:57 : view
09:00 : it's going to have a model of question
09:04 : oh interesting so this one we just tell
09:07 : it what the model class is whereas this
09:11 : one
09:12 : we didn't do that but instead of that we
09:14 : um
09:15 : we wrote the actual code
09:18 : that performs the query so
09:21 : because we're controlling the code that
09:24 : performs the query we we didn't supply
09:26 : the model class whereas here we supply
09:29 : the model class
09:31 : and i guess let the framework itself
09:36 : sort of
09:40 : figure out
09:41 : how to use our model class to make a
09:44 : query
09:45 : and i bet there's like a default
09:48 : behavior which we're just going to use
09:52 : for this case
09:54 : so here let's compare these two so here
10:00 : the template name got moved here and
10:04 : then all we're doing is the uh
10:07 : the question is this model class goes
10:11 : here and it kind of was able to infer
10:14 : that we should do this i guess
10:17 : and also we should do this so this the
10:21 : fact that this question
10:23 : is the name
10:26 : of the
10:27 : of the variable to be used in the
10:30 : template that was inferred i guess like
10:34 : like what i mean is this in this
10:36 : detail.html template
10:38 : we make use of a variable called
10:40 : question
10:42 : which here we define that in this
10:44 : context dictionary um in the new version
10:49 : detail view which is going to replace
10:51 : this
10:53 : we don't even define this explicitly so
10:56 : the name question must be inferred from
10:58 : the name of the model
11:01 : so basically all of this code was
11:04 : inferred
11:05 : but it's going to be inferred by this
11:07 : generic that detail view so the generic
11:10 : there's different things we're using
11:14 : kind of
11:16 : we're using a list view and we're also
11:18 : using a detail view which
11:20 : i suppose each of them have a slightly
11:22 : different
11:24 : behavior and assumptions it makes
11:27 : about
11:30 : how
11:31 : they're supposed to be used
11:34 : okay i'll finish this off
11:45 : okay
11:46 : model is also question
11:50 : and then template name
11:52 : is polls results dot html
11:56 : and
11:57 : that
11:58 : replaces this one and i would say this
12:02 : results one is so similar to this detail
12:05 : one
12:06 : um the only difference is the template
12:09 : name is different
12:11 : really
12:13 : yeah
12:15 : and
12:17 : yeah i guess
12:19 : if we're translating it
12:22 : from this form
12:26 : um to to this and this
12:31 : to this and this
12:34 : um
12:35 : we have removed like we've have lessened
12:38 : the amount of code you would have to
12:40 : duplicate
12:42 : but um
12:44 : there's still some duplication namely
12:47 : that
12:47 : and that
12:49 : which is interesting and and and sort of
12:53 : well this this this having to define a
12:56 : class that's a little bit of overhead
12:59 : okay
13:01 : i guess that's it
13:04 : am i to believe that this is to work the
13:08 : same way as before
13:11 : uh
13:12 : template does not exist
13:15 : pulls that
13:16 : details
13:18 : is it detail not details
13:21 : singular
13:24 : it is singular okay
13:26 : so everything works as before
13:29 : um
13:30 : and this is
13:32 : fine and if we went to the
13:36 : normal detail this is normal detail view
13:39 : and then this is the
13:42 : top level view
13:44 : okay
13:47 : so that's all the code for part four i'm
13:50 : gonna read this part a little bit
13:54 : to get some more detail we're using two
13:56 : generic views here the list view and the
13:59 : detail view respectively those two views
14:02 : abstract the concepts of displaying a
14:05 : list of objects and display a detail
14:08 : page for a particular type of object
14:10 : each generic view needs to know what
14:12 : model it will be acting upon
14:17 : this is provided using the model
14:18 : attribute
14:20 : right although we didn't provide it to
14:22 : the list view did we the list view
14:26 : we didn't tell it what the model
14:29 : was
14:30 : it's generic viewing
14:32 : the detail view generic view
14:35 : expects the primary key value captured
14:38 : from the url to be called pk
14:42 : so we're changing
14:45 : question mark id to pk right by default
14:47 : the detail view generic view
14:51 : uses a template
14:53 : called app name
14:55 : model name dash detail dot html in our
14:59 : case it would use the template
15:02 : pose slash question detail so
15:05 : so there's a default if we use their
15:07 : default naming scheme that we wouldn't
15:10 : have needed to specify the template name
15:14 : even
15:25 : so um
15:27 : also specify the template name for the
15:29 : results
15:30 : list view
15:33 : that then this ensures that the results
15:35 : view and the detail will have a
15:36 : different appearance when rendered even
15:39 : though they're both a detail view behind
15:41 : the scenes
15:42 : similarly list view generic view uses a
15:44 : default template
15:47 : using this convention but we overrode it
15:51 : with this value in previous parts of the
15:53 : tutorial
15:55 : the templates have been provided with a
15:57 : context
15:58 : that contains question
16:01 : and latest question list context
16:03 : variables for detail view the question
16:05 : variable is provided automatically since
16:08 : we are using a django model question
16:11 : and you can ask
16:13 : the the model class it's for its name
16:17 : yeah
16:18 : django is able to determine an
16:20 : appropriate name for the context
16:22 : variable however for a list view the
16:24 : automatically generated context variable
16:26 : is question list
16:28 : to override this provided
16:30 : we provide the context object name
16:34 : attribute specifying that we want to use
16:38 : latest question list
16:40 : as uh instead oh as an alternative
16:43 : approach you could change your template
16:45 : to match the new default context
16:47 : variable
16:49 : okay
16:50 : i want to try that alternative which is
16:53 : instead of telling it what the context
16:56 : object name is i don't
16:58 : and then i want to go to this index html
17:03 : and change
17:04 : wherever it says latest question list
17:07 : i'm going to change that to question
17:09 : list
17:11 : um
17:12 : the problem is i don't think this will
17:14 : work because we actually didn't tell
17:16 : the generic view list view what the
17:19 : model is
17:21 : so
17:22 : probably just not gonna work
17:27 : oh
17:29 : it did work
17:31 : how did it know
17:32 : maybe because
17:35 : maybe it knows because the the query set
17:38 : that i return consists of question
17:40 : objects
17:42 : what if i um
17:44 : change this
17:45 : and i
17:46 : returned choice objects instead
17:51 : will that break everything
18:01 : no polls
18:04 : are available
18:09 : oh
18:12 : oh we don't have question lists
18:17 : i bet we have choice list though
18:27 : uh
18:28 : [Music]
18:31 : okay
18:32 : i think that's probably what happened
18:34 : okay
18:36 : yes i believe that is what happened like
18:39 : if i change this to question
18:41 : that objects
18:43 : at all
18:45 : then we'll have the questions
18:49 : okay so
18:54 : okay
18:55 : that's fine
18:57 : so
18:58 : we'll do it like this and um
19:00 : yeah that's the end of part four
19:03 : i'll see you over in part five