> ## Documentation Index
> Fetch the complete documentation index at: https://cockroachlabs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Build a Python App with CockroachDB and Django

export const InternalLink = ({version, path = "", children, ...props}) => {
  let detectedVersion = version || "stable";
  if (typeof window !== 'undefined' && !version) {
    const match = window.location.pathname.match(/\/docs\/([^/]+)/);
    if (match) {
      detectedVersion = match[1];
    }
  }
  const normalizedPath = path.startsWith("/") ? path.slice(1) : path;
  return <a href={`/docs/${detectedVersion}/${normalizedPath}`} {...props}>
      {children}
    </a>;
};

export const InternalLink = ({version, path = "", children, ...props}) => {
  let detectedVersion = version || "stable";
  if (typeof window !== 'undefined' && !version) {
    const match = window.location.pathname.match(/\/docs\/([^/]+)/);
    if (match) {
      detectedVersion = match[1];
    }
  }
  const normalizedPath = path.startsWith("/") ? path.slice(1) : path;
  return <a href={`/docs/${detectedVersion}/${normalizedPath}`} {...props}>
      {children}
    </a>;
};

This tutorial shows you how build a simple Python application with CockroachDB and the [Django](https://www.djangoproject.com/) framework.

CockroachDB supports Django versions 3.1+.

<Note>
  The example code and instructions on this page use Python 3.9 and Django 3.1.
</Note>

## Step 1. Start CockroachDB

<Tabs>
  <Tab title="Use CockroachDB Cloud">
    ### Choose your installation method

    You can create a CockroachDB Basic cluster using either the CockroachDB Cloud Console, a web-based graphical user interface (GUI) tool, or `ccloud`, a command-line interface (CLI) tool.

    <Tabs>
      <Tab title="Cloud Console (GUI)">
        ### Create a free cluster

        <Note>
          Organizations without billing information on file can only create one CockroachDB Basic cluster.
        </Note>

        1. If you haven't already, [sign up for a CockroachDB Cloud account](https://cockroachlabs.cloud/signup?referralId=docs_python_django).
        2. [Log in](https://cockroachlabs.cloud/) to your CockroachDB Cloud account.
        3. On the **Clusters** page, click **Create cluster**.
        4. On the **Select a plan** page, select **Basic**.
        5. On the **Cloud & Regions** page, select a cloud provider (GCP or AWS) in the **Cloud provider** section.
        6. In the **Regions** section, select a region for the cluster. Refer to <InternalLink version="cockroachcloud" path="regions">CockroachDB Cloud Regions</InternalLink> for the regions where CockroachDB Basic clusters can be deployed. To create a multi-region cluster, click **Add region** and select additional regions.
        7. Click **Next: Capacity**.
        8. On the **Capacity** page, select **Start for free**. Click **Next: Finalize**.
        9. On the **Finalize** page, click **Create cluster**.

           Your cluster will be created in a few seconds and the **Create SQL user** dialog will display.

        ### Create a SQL user

        The **Create SQL user** dialog allows you to create a new SQL user and password.

        1. Enter a username in the **SQL user** field or use the one provided by default.
        2. Click **Generate & save password**.
        3. Copy the generated password and save it in a secure location.
        4. Click **Next**.

           Currently, all new SQL users are created with admin privileges. For more information and to change the default settings, see <InternalLink version="cockroachcloud" path="managing-access#manage-sql-users-on-a-cluster">Manage SQL users on a cluster</InternalLink>.

        ### Get the root certificate

        The **Connect to cluster** dialog shows information about how to connect to your cluster.

        1. Select **General connection string** from the **Select option** dropdown.
        2. Open a new terminal on your local machine, and run the **CA Cert download command** provided in the **Download CA Cert** section. The client driver used in this tutorial requires this certificate to connect to CockroachDB Cloud.

        ### Get the connection string

        Open the **General connection string** section, then copy the connection string provided and save it in a secure location.

        <Note>
          The connection string is pre-populated with your username, password, cluster name, and other details. Your password, in particular, will be provided *only once*. Save it in a secure place (Cockroach Labs recommends a password manager) to connect to your cluster in the future. If you forget your password, you can reset it by going to the **SQL Users** page for the cluster, found at `https://cockroachlabs.cloud/cluster/<CLUSTER ID>/users`.
        </Note>
      </Tab>

      <Tab title="ccloud CLI">
        Follow these steps to create a CockroachDB Basic cluster using the `ccloud` CLI tool.

        <Note>
          The `ccloud` CLI tool is in Preview.
        </Note>

        ### Install `ccloud`

        <Tabs>
          <Tab title="Mac">
            You can install `ccloud` using either Homebrew or by downloading the binary.

            #### Use Homebrew

            1. [Install Homebrew](http://brew.sh/).
            2. Install using the `ccloud` tap:

               ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
               brew install cockroachdb/tap/ccloud
               ```

            #### Download the binary

            In a terminal, enter the following command to download and extract the `ccloud` binary and add it to your `PATH`:

            ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
            curl https://binaries.cockroachdb.com/ccloud/ccloud_darwin-amd64_.tar.gz | tar -xJ && cp -i ccloud /usr/local/bin/
            ```

            Use the ARM 64 binary if you have an M-series Mac:

            ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
            curl https://binaries.cockroachdb.com/ccloud/ccloud_darwin-arm64_.tar.gz | tar -xJ && cp -i ccloud /usr/local/bin/
            ```
          </Tab>

          <Tab title="Linux">
            In a terminal, enter the following command to download and extract the `ccloud` binary and add it to your `PATH`:

            ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
            curl https://binaries.cockroachdb.com/ccloud/ccloud_linux-amd64_.tar.gz | tar -xz && cp -i ccloud /usr/local/bin/
            ```
          </Tab>

          <Tab title="Windows">
            In a PowerShell window, enter the following command to download and extract the `ccloud` binary and add it to your `PATH`:

            ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
            $ErrorActionPreference = "Stop"; [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; $ProgressPreference = 'SilentlyContinue'; $null = New-Item -Type Directory -Force $env:appdata/ccloud; Invoke-WebRequest -Uri https://binaries.cockroachdb.com/ccloud/ccloud_windows-amd64_.zip -OutFile ccloud.zip; Expand-Archive -Force -Path ccloud.zip; Copy-Item -Force ccloud/ccloud.exe -Destination $env:appdata/ccloud; $Env:PATH += ";$env:appdata/ccloud"; # We recommend adding ";$env:appdata/ccloud" to the Path variable for your system environment. See https://docs.microsoft.com/powershell/module/microsoft.powershell.core/about/about_environment_variables#saving-changes-to-environment-variables for more information.
            ```
          </Tab>
        </Tabs>

        ### Run `ccloud quickstart` to create a new cluster, create a SQL user, and retrieve the connection string.

        The easiest way of getting started with CockroachDB Cloud is to use `ccloud quickstart`. The `ccloud quickstart` command guides you through logging in to CockroachDB Cloud, creating a new CockroachDB Basic cluster, and connecting to the new cluster. Run `ccloud quickstart` and follow the instructions:

        ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
        ccloud quickstart
        ```

        The `ccloud quickstart` command will open a browser window to log you in to CockroachDB Cloud. If you are new to CockroachDB Cloud, you can register using one of the single sign-on (SSO) options, or create a new account using an email address.

        The `ccloud quickstart` command will prompt you for the cluster name, cloud provider, and cloud provider region, then ask if you want to connect to the cluster. Each prompt has default values that you can select, or change if you want a different option.

        Select **General connection string**, then copy the connection string displayed and save it in a secure location. The connection string is the line starting `postgresql://`.

        ```
        ? How would you like to connect? General connection string
        Retrieving cluster info: succeeded
         Downloading cluster cert to /Users/maxroach/.postgresql/root.crt: succeeded
        postgresql://maxroach:ThisIsNotAGoodPassword@blue-dog-147.6wr.cockroachlabs.cloud:26257/defaultdb?sslmode=verify-full&sslrootcert=%2FUsers%2Fmaxroach%2F.postgresql%2Froot.crt
        ```
      </Tab>
    </Tabs>
  </Tab>

  <Tab title="Use a Local Cluster">
    1. If you haven't already, <InternalLink path="install-cockroachdb">download the CockroachDB binary</InternalLink>.
    2. Run the <InternalLink path="cockroach-start-single-node">`cockroach start-single-node`</InternalLink> command:

       ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
       $ cockroach start-single-node --advertise-addr 'localhost' --insecure
       ```

       This starts an insecure, single-node cluster.
    3. Take note of the following connection information in the SQL shell welcome text:

       ```
       CockroachDB node starting at 2021-08-30 17:25:30.06524 +0000 UTC (took 4.3s)
       build:               CCL v21.1.6 @ 2021/07/20 15:33:43 (go1.15.11)
       webui:               http://localhost:8080
       sql:                 postgresql://root@localhost:26257?sslmode=disable
       ```

       You'll use the `sql` connection string to connect to the cluster later in this tutorial.

    <Danger>
      The `--insecure` flag used in this tutorial is intended for non-production testing only. To run CockroachDB in production, use a secure cluster instead.
    </Danger>
  </Tab>
</Tabs>

## Step 2. Get the sample code

Clone the code's GitHub repo:

```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
$ git clone https://github.com/cockroachlabs/example-app-python-django/
```

The project directory structure should look like this:

```
├── Dockerfile
├── README.md
├── cockroach_example
│   ├── cockroach_example
│   │   ├── __init__.py
│   │   ├── asgi.py
│   │   ├── migrations
│   │   │   ├── 0001_initial.py
│   │   │   └── __init__.py
│   │   ├── models.py
│   │   ├── settings.py
│   │   ├── urls.py
│   │   ├── views.py
│   │   └── wsgi.py
│   └── manage.py
└── requirements.txt
```

## Step 3. Install the application requirements

To use CockroachDB with Django, the following modules are required:

* [`django`](https://docs.djangoproject.com/en/3.1/topics/install/)
* [`psycopg2`](https://pypi.org/project/psycopg2/) (recommended for production environments) or [`psycopg2-binary`](https://pypi.org/project/psycopg2-binary/) (recommended for development and testing).
* [`django-cockroachdb`](https://github.com/cockroachdb/django-cockroachdb)

<Note>
  The major version of `django-cockroachdb` must correspond to the major version of `django`. The minor release numbers do not need to match.
</Note>

The `requirements.txt` file at the top level of the `example-app-python-django` project directory contains a list of the requirements needed to run this application:

```python theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
psycopg2-binary
django==5.0.1
django-cockroachdb==5.0
```

This tutorial uses [`virtualenv`](https://virtualenv.pypa.io) for dependency management.

1. Install `virtualenv`:

   ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   $ pip install virtualenv
   ```

2. At the top level of the app's project directory, create and then activate a virtual environment:

   ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   $ virtualenv env
   ```

   ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   $ source env/bin/activate
   ```

3. Install the modules listed in `requirements.txt` to the virtual environment:

   ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   $ pip install -r requirements.txt
   ```

## Step 4. Build out the application

### Configure the database connection

Open `cockroach_example/cockroach_example/settings.py`, and configure [the `DATABASES` dictionary](https://docs.djangoproject.com/en/3.2/ref/settings/#databases) to connect to your cluster using the connection parameters that you copied earlier.

```python theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
DATABASES = {
    'default': {
        'ENGINE': 'django_cockroachdb',
        'NAME': '{database}',
        'USER': '{username}',
        'PASSWORD': '{password}',
        'HOST': '{host}',
        'PORT': '{port}',
        'OPTIONS': {
            'sslmode': 'verify-full'
        },
    },
}
```

For more information about configuration a Django connection to CockroachDB Standard, see [Connect to a CockroachDB Cluster](connect-to-the-database.html?filters=python\&filters=django).

After you have configured the app's database connection, you can start building out the application.

### Models

Start by building some [models](https://docs.djangoproject.com/en/3.1/topics/db/models/), defined in a file called `models.py`. You can copy the sample code below and paste it into a new file, or you can download the file directly.

```python theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
from django.db import models

class Customers(models.Model):
    id = models.UUIDField(
        primary_key=True,
        default=uuid.uuid4,
        editable=False)
    name = models.CharField(max_length=250)

class Products(models.Model):
    id = models.UUIDField(
        primary_key=True,
        default=uuid.uuid4,
        editable=False)
    name = models.CharField(max_length=250)
    price = models.DecimalField(max_digits=18, decimal_places=2)

class Orders(models.Model):
    id = models.UUIDField(
        primary_key=True,
        default=uuid.uuid4,
        editable=False)
    subtotal = models.DecimalField(max_digits=18, decimal_places=2)
    customer = models.ForeignKey(
        Customers, on_delete=models.CASCADE, null=True)
    product = models.ManyToManyField(Products)
```

In this file, we define some simple classes that map to the tables in the cluster.

### Views

Next, build out some [class-based views](https://docs.djangoproject.com/en/3.1/topics/class-based-views/) for the application in a file called `views.py`. You can copy the sample code below and paste it into a new file, or you can download the file directly.

```python theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
from django.http import JsonResponse, HttpResponse
from django.utils.decorators import method_decorator
from django.views.generic import View
from django.views.decorators.csrf import csrf_exempt
from django.db import Error, IntegrityError
from django.db.transaction import atomic
from psycopg2 import errorcodes

from .models import *

# Warning: Do not use retry_on_exception in an inner nested transaction.

def retry_on_exception(num_retries=3, on_failure=HttpResponse(status=500), delay_=0.5, backoff_=1.5):
    def retry(view):
        def wrapper(*args, **kwargs):
            delay = delay_
            for i in range(num_retries):
                try:
                    return view(*args, **kwargs)
                except IntegrityError as ex:
                    if i == num_retries - 1:
                        return on_failure
                    elif getattr(ex.__cause__, 'pgcode', '') == errorcodes.SERIALIZATION_FAILURE:
                        time.sleep(delay)
                        delay *= backoff_
                except Error as ex:
                    return on_failure
        return wrapper
    return retry

class PingView(View):
    def get(self, request, *args, **kwargs):
        return HttpResponse("python/django", status=200)

@method_decorator(csrf_exempt, name='dispatch')
class CustomersView(View):
    def get(self, request, id=None, *args, **kwargs):
        if id is None:
            customers = list(Customers.objects.values())
        else:
            customers = list(Customers.objects.filter(id=id).values())
        return JsonResponse(customers, safe=False)

    @retry_on_exception(3)
    @atomic
    def post(self, request, *args, **kwargs):
        form_data = json.loads(request.body.decode())
        name = form_data['name']
        c = Customers(name=name)
        c.save()
        return HttpResponse(status=200)

    @retry_on_exception(3)
    @atomic
    def delete(self, request, id=None, *args, **kwargs):
        if id is None:
            return HttpResponse(status=404)
        Customers.objects.filter(id=id).delete()
        return HttpResponse(status=200)

    # The PUT method is shadowed by the POST method, so there doesn't seem
    # to be a reason to include it.

@method_decorator(csrf_exempt, name='dispatch')
class ProductView(View):
    def get(self, request, id=None, *args, **kwargs):
        if id is None:
            products = list(Products.objects.values())
        else:
            products = list(Products.objects.filter(id=id).values())
        return JsonResponse(products, safe=False)

    @retry_on_exception(3)
    @atomic
    def post(self, request, *args, **kwargs):
        form_data = json.loads(request.body.decode())
        name, price = form_data['name'], form_data['price']
        p = Products(name=name, price=price)
        p.save()
        return HttpResponse(status=200)

    # The REST API outlined in the github does not say that /product/ needs
    # a PUT and DELETE method

@method_decorator(csrf_exempt, name='dispatch')
class OrdersView(View):
    def get(self, request, id=None, *args, **kwargs):
        if id is None:
            orders = list(Orders.objects.values())
        else:
            orders = list(Orders.objects.filter(id=id).values())
        return JsonResponse(orders, safe=False)

    @retry_on_exception(3)
    @atomic
    def post(self, request, *args, **kwargs):
        form_data = json.loads(request.body.decode())
        c = Customers.objects.get(id=form_data['customer']['id'])
        o = Orders(subtotal=form_data['subtotal'], customer=c)
        o.save()
        for p in form_data['products']:
            p = Products.objects.get(id=p['id'])
            o.product.add(p)
        o.save()
        return HttpResponse(status=200)
```

This file defines the application's views as classes. Each view class corresponds to one of the table classes defined in `models.py`. The methods of these classes define read and write transactions on the tables in the database.

Importantly, the file defines a <InternalLink path="transactions#transaction-retries">transaction retry loop</InternalLink> in the decorator function `retry_on_exception()`. This function decorates each view method, ensuring that transaction ordering guarantees meet the ANSI [SERIALIZABLE](https://wikipedia.org/wiki/Isolation_\(database_systems\)#Serializable) isolation level. For more information about how transactions (and retries) work, see <InternalLink path="transactions">Transactions</InternalLink>.

### URL routes

Lastly, define some [URL routes](https://docs.djangoproject.com/en/3.1/topics/http/urls/) in a file called `urls.py`. You can copy the sample code below and paste it into the existing `urls.py` file, or you can download the file directly and replace the existing one.

```python theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
from django.contrib import admin
from django.urls import path

from .views import CustomersView, OrdersView, PingView, ProductView

urlpatterns = [
    path('admin/', admin.site.urls),

    path('ping/', PingView.as_view()),

    # Endpoints for customers URL.
    path('customer/', CustomersView.as_view(), name='customers'),
    path('customer/<uuid:id/', CustomersView.as_view(), name='customers'),

    # Endpoints for customers URL.
    path('product/', ProductView.as_view(), name='product'),
    path('product/<uuid:id/', ProductView.as_view(), name='product'),

    path('order/', OrdersView.as_view(), name='order'),
]
```

## Step 5. Initialize the database

In the top `cockroach_example` directory, use the [`manage.py` script](https://docs.djangoproject.com/en/3.1/ref/django-admin/) to create [Django migrations](https://docs.djangoproject.com/en/3.1/topics/migrations/) that initialize the database for the application:

```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
$ python manage.py makemigrations cockroach_example
```

```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
$ python manage.py migrate
```

This initializes the tables defined in `models.py`, in addition to some other tables for the admin functionality included with Django's starter application.

## Step 6. Run the app

1. In a different terminal, navigate to the top of the `cockroach_example` directory, and start the app:

   ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   $ python manage.py runserver 0.0.0.0:8000
   ```

   The output should look like this:

   ```
   ...
   Starting development server at http://0.0.0.0:8000/
   Quit the server with CONTROL-C.
   ```

   To perform simple reads and writes to the database, you can send HTTP requests to the application server listening at `http://0.0.0.0:8000/`.

2. In a new terminal, use `curl` to send a POST request to the application:

   ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   $ curl --header "Content-Type: application/json" \
   --request POST \
   --data '{"name":"Carl"}' http://0.0.0.0:8000/customer/
   ```

   This request inserts a new row into the `cockroach_example_customers` table.

3. Send a GET request to read from the `cockroach_example_customers` table:

   ```shell theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   $ curl http://0.0.0.0:8000/customer/
   ```

   ```
   [{"id": "bb7d6c4d-efb3-45f8-b790-9911aae7d8b2", "name": "Carl"}]
   ```

   You can also query the table directly in the <InternalLink path="cockroach-sql">SQL shell</InternalLink> to see the changes:

   ```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   > SELECT * FROM cockroach_example_customers;
   ```

   ```
                      id                  | name
   ---------------------------------------+-------
     bb7d6c4d-efb3-45f8-b790-9911aae7d8b2 | Carl
   (1 row)
   ```

4. Enter **Ctrl+C** to stop the application.

## What's next?

Read more about writing a [Django app](https://docs.djangoproject.com/en/3.1/intro/tutorial01/).

You might also be interested in the following pages:

* [Client Connection Parameters](connection-parameters)
* [Connection Pooling](connection-pooling)
* [Data Replication](demo-replication-and-rebalancing)
* [CockroachDB Resilience](demo-cockroachdb-resilience)
* [Replication & Rebalancing](demo-replication-and-rebalancing)
* [Cross-Cloud Migration](demo-automatic-cloud-migration)
* [Automated Operations](orchestrate-a-local-cluster-with-kubernetes-insecure)