I have been building Django based web application for a while now. One design/request I get often is a REST API. Once the model data is exposed in REST, one can truly build a complete separate frontend using things like Angular, react, and whatever you fancy. I have tried a couple times myself following this architecture. On one hand it gives a lot of flexibility and it looks nice, too ← front end technology is a lot of "{}", but it does look quite nice, and responsive, too. But on the other, REST is a thing few understands well except it is an API through which you can CRUD. Honestly, I don't even understand yet how authentication is done, what is a good balance between massaging data (in Tastypie's term, (de)-hydration) and exposing data model raw.

    Anyway, here I want to document a practice I use, a really rudimentary one, of making django model available as REST resource through Tastypie.

    1. Django model reference
    2. Tastypie

    Let's say you are building a site called mysite, and in it it has an application called myapp. So the file structure will be like gitroot/mysite/urls.py for site-level URLs, and gitroot/myapp/urls.py for app-level patterns. The confusing part is that myapp/urls.py will be folded into mysite/urls.py. So the thought is that a site can have multiple applications, each defining its own sub-pattern, while the mysite/urls.py has the first run of the match before handing URL to myapp/urls.py to match further. So it's a matter of matching order.

    Anyway. So building a REST can be broken down into 5 steps:

    Step 1: create an API varialbe name.

    Define an object v1_api in myapp/api.py. Name is not important at all. It is a Tastypie's Api object, therefore it comes with an army of capabilities:

    from tastypie.api import Api
    v1_api = Api(api_name='v1')

    Step 2: wire URL patterns

    v1_api defined in the previous step comes with a list of REST url patterns, and this is the beauty of Tastypie. So all we need to do is make these sub-patterns available through URL matching. As explained above, we need to wire these into mysite/urls.py:

    from myapp.api import v1_api as myapp_api  <-- the variable we defined
    urlpatterns = patterns(
        # REST
        url(r'^mysite/api/myapp/',    <-- pattern matching
            include(myapp_api.urls)), <-- sub-pattern handler

    Step 3: define your django DB model

    Nothing fancy here. Just the old school of data modeling.

    Step 4: transform DB model to a resource model

    REST speaks resources. Packaging a DB model into a resource is quite simple:

    from tastypie.resources import ModelResource
    from myapp.models import MyModel  <-- import DB model
    v1_api = Api(api_name='v1') <-- we have seen this one (see "step 1")
    class MyModelResource(ModelResource):
        class Meta:
            queryset = MyModel.objects.all()  <-- data set to display in list
            resource_name = "mymodels" <-- string used in REST url "/mymodels/"
    v1_api.register(MyModelResource())  <-- expose it to URL

    This is the simpliest example to make magic happen. What's more you can do with this now?

    1. .objects.all(): you don't have to expose everything. Any queryset is adequate. REST will allow filtering as well. So just need to be aware what your decision means.
    2. de-hydrate: this is how you can massage your data set (essentially serializing and de-serializing) before you send data to user or taking data from data to DB.
    3. foreign key reverse lookup

    Django defines reverse lookup by defining a related name in model:

    class Datacenter(BaseModel):
    class Cluster(BaseModel):
        datacenter = models.ForeignKey("Datacenter",
                                       related_name="clusters") <-- related_name!

    Consequently, DataCenterResource reverse lookup to cluster will be like this:

    class DatacenterResource(MyModelResource):
      clusters = fields.ToManyField("vx.api.ClusterResource", <-- FK resource
                                    attribute="clusters", <-- django related name

    step 5: enjoy

    Now go to mysite/api/myapp/mymodels (mysite/api/myapp/ part is defined in "step 1", mymodels part is defined in "step 4"), it should show the queryset (defined in "step 4"). With REST, you can also do things like ?format=json or ?format=yaml, and ?a_model_field__gt= type of filtering. Cool huh!?

    — by Feng Xia



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