Linking ressource together

Now that you have users and address, you want to link them together. Adding a reference from a user to his user.

Not all the datastore can handle this type of relation but hopefully, the SQLiteDataStore does.

First you will need to change your UserModel definition:

fields = [models.StringField(name="country", required=True),
          models.StringField(name="city", required=True),
          models.StringField(name="street", required=True),
          models.IntegerField(name="number", required=True),
          models.IntForeign(name="user",
                            foreign={"table": "users",
                                     "column": "id",
                                     }
                            ),
          models.PkField(name="id", required=True)
          ]

The part we added is:

models.IntForeign(name="address",
                  foreign={"table": "address",
                           "column": "id",
                           }
                  ),

This will add a foreign key constrain on the user ensuring the address id you give corresspond to an existing address.

• table : is the table of the ressource your are linking
• column: is the column you will check for the constrain

Note

unfortunately, at the time of writing, there is no way to update the schema automaticaly. You will need either to destroy your database (Python Rest Framework will create a fresh one) or do an alter table by hands. As this is just a tutorial, we will choose the second option and delete the file “adress.db”

It’s also important to note the your endpoints must be listed in the Wrapper in the order of foreing keys. First the model to link to, then the model that will be linked

Adding an adress

curl -i -H "Content-type: application/json" -X POST -d
'{"country":"France", "city": "Paris", "street": "quais de Valmy",
"number": 45}' http://localhost:5000/address/

HTTP/1.0 201 CREATED
Location: http://localhost:5000/address/1/
Content-Type: application/json
Content-Length: 0
Server: Werkzeug/0.8.3 Python/2.7.2
Date: Tue, 15 Oct 2013 17:23:49 GMT

Create a user linked to an address

Because, as the API developper you know that http://localhost:5000/address/1/ corresond to the address with the “id” 1 you can create a user:

curl -i -H "Content-type: application/json" -X POST -d
'{"first_name":"Super", "last_name": "Dupont", "address": 1}'
http://localhost:5000/users/

HTTP/1.0 201 CREATED
Location: http://localhost:5000/users/1/
Content-Type: application/json
Content-Length: 0
Server: Werkzeug/0.8.3 Python/2.7.2
Date: Tue, 15 Oct 2013 17:27:34 GMT

You can check that your Foreign constrain is working with:

curl -i -H "Content-type: application/json" -X POST -d
'{"first_name":"Super", "last_name": "Man", "address": 2}'
http://localhost:5000/users/

HTTP/1.0 400 BAD REQUEST
Content-Type: application/json
Content-Length: 38
Server: Werkzeug/0.8.3 Python/2.7.2
Date: Tue, 15 Oct 2013 17:30:03 GMT

{"error": "address does not validate"}

This fail because address 2 does not exists.

Retreive the adress of a user

If you now the user, it’s easy to get the adress.

First get the user:

curl -i http://localhost:5000/users/1/
HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 90
Server: Werkzeug/0.8.3 Python/2.7.2
Date: Tue, 15 Oct 2013 17:42:18 GMT

{
"address": 1,
"first_name": "Super",
"last_name": "Dupont",
"ressource_uri": "/users/1/"
}

His adress has the id “1”. We can issue a request:

curl -i http://localhost:5000/address/1/
HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 112
Server: Werkzeug/0.8.3 Python/2.7.2
Date: Tue, 15 Oct 2013 17:44:07 GMT

{
    "city": "Paris",
    "country": "France",
    "number": 45,
    "ressource_uri": "/address/1/",
    "street": "quais de Valmy"
}

Retreive users from an adress

The same apply in the other side. As we know the adress id:

curl -i http://localhost:5000/users/?address=1
HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 228
Server: Werkzeug/0.8.3 Python/2.7.2
Date: Tue, 15 Oct 2013 17:46:13 GMT

{
    "meta": {
        "count": 20,
        "filters": {
            "address": "1"
        },
        "next": "null",
        "offset": 0,
        "previous": "null",
        "total_count": 1
    },
    "object_list": [
        {
            "address": 1,
            "first_name": "Super",
            "last_name": "Dupont",
            "ressource_uri": "/users/1/"
        }
    ]
}

next: Representing relations