Create database view from django model

问题:

I learned sql "view" as a virtual table to facilitate the SQL operations, like

MySQL [distributor]> CREATE VIEW CustomerEMailList AS
    -> SELECT cust_id, cust_name, cust_email
    -> FROM Customers
    -> WHERE cust_email IS NOT NULL;
Query OK, 0 rows affected (0.026 sec)

MySQL [distributor]> select * from customeremaillist;
+------------+---------------+-----------------------+
| cust_id    | cust_name     | cust_email            |
+------------+---------------+-----------------------+
| 1000000001 | Village Toys  | [e-mail] |
| 1000000003 | Fun4All       | [e-mail]    |
| 1000000004 | Fun4All       | [e-mail] |
| 1000000005 | The Toy Store | [e-mail]   |
| 1000000006 | toy land      | [e-mail]       |
+------------+---------------+-----------------------+
5 rows in set (0.014 sec)

When I checked the Django documentation subsequently, there are no such functionality to create a virtual "model table" which could simplify the data manipulation.

Should I forget the virtual table "view" when using Django ORM?

回答1:

Django has - as far as I know at the moment - no builtin support for views.

But you can construct such views, by using the django-database-view package.

After installing the package (for example with pip):

 pip install django-database-view

Furthermore the dbview app has to be registered in the settings.py file:

# settings.py

INSTALLED_APPS = (
    # ...
    'dbview',
    # ...
)

Now you can construct a view, this looks a bit similar to the construction of a model, except that you need to implement a view(..) function that specifies the query behind the view. Something similar to:

from django.db import models
from dbview import DbView

class CustomerEMailList(DbView):
    cust = models.OneToOneField(Customer, primary_key=True)
    cust_name = models.CharField()
    cust_email = models.CharField()

    @classmethod
    def view(klass):
        qs = (Customers.objects.filter(cust_email__isnull=False)
                               .values('cust_id', 'cust_name', 'cust_email'))
        return str(qs.query)

Now we can make a migrations:

./manage.py makemigrations

Now in the migration, we need to make a change: the calls to migrations.CreateModel that are related to the constructed view(s), should be changed to the CreateView of the dbview module. Something that looks like:

from django.db import migrations
from dbview import CreateView

class Migration(migrations.Migration):

    dependencies = []

    operations = [
        migrations.CreateView(
            name='CustomerEMailList',
            fields=[
                # ...
            ],
        ),
    ]

回答2:

According to the Django ORM Cookbook by Agiliq, you can do it like the following.

Create view:

create view temp_user as
select id, first_name from auth_user;

Create a model which is not managed and naming a db_table explicitly:

class TempUser(models.Model):
    first_name = models.CharField(max_length=100)

    class Meta:
        managed = False
        db_table = "temp_user"

You'll be able to query then, but you'll receive an error once you try to update.

Query like always:

TempUser.objects.all().values()

I haven't tried this yet, but I certainly will.