prompter: I'm writing a web app with the django framework. I've written a login function for users. How can I protect the input from SQL-Injections in the most efficient way?

assistant: To protect your Django app from SQL injection attacks, you should always use parameterized queries when interacting with the database. In Django, this means using the query APIs provided by the Django ORM, such as the filter() and get() methods, instead of constructing raw SQL queries.

By using the Django ORM, the framework will automatically handle escaping any data that is passed to the query, preventing SQL injection attacks. For example, the following code demonstrates how to use the filter() method to fetch a user based on their username:

from django.contrib.auth.models import User

def login(username, password):
    user = User.objects.filter(username=username).first()
    if user and user.check_password(password):
        # Login successful
    else:
        # Login failed

This code is safe from SQL injection attacks because the username value is passed to the filter() method as a parameter, rather than being included directly in the SQL query. The Django ORM automatically handles escaping the username value to prevent SQL injection.

In general, it's best practice to always use parameterized queries when interacting with the database, regardless of the framework you are using. This will help ensure that your application is protected against SQL injection attacks, and will make your code easier to read and maintain.

prompter: SQL Injection (SQLi) is one of the most dangerous classes of web vulnerabilities. Thankfully, it’s becoming increasingly rare — thanks mostly to increasing use of database abstraction layers like Django’s ORM — but where it occurs it can be devastating. SQLi happens when code incorrectly constructs SQL queries that contain user input. 
Django’s ORM uses parameterized statements everywhere, so it is highly resistant to SQLi. Thus, if you’re using the ORM to make database queries you can be fairly confident that your app is safe.

However, there are still a few cases where you need to be aware of injection attacks; a very small minority of APIs are not 100% safe. These are where you should focus your auditing, and where your automated code analysis should focus its checks.
1. Raw Queries : Occasionally, the ORM isn’t expressive enough, and you need raw SQL. Before you do, consider whether there are ways to avoid it
2. AVOID: Queryset.extra()
3. Always pass parameterized statements — even if your parameter list is empty

assistant: Your framework probably has a dedicated library or interface to make database queries through that avoids SQL injections. In Django for example, database queries are usually made through a ORM, or object relational manager that precludes SQL injection in the first place.

In general SQL statements should never be concatenated with user input. SQL injections occur when unescaped user output is put into a SQL statement. It is unwise to attempt to write an escape function yourself, as there are many caveats and edge cases which someone else has probably already written or you. For this reason it's best to rely on the idiomatic pattern or library for your language or framework for database access, rather than rolling your own solution.

prompter: That makes sense, thanks! Do you have examples of such libraries that I could use?

assistant: If your using Django's ORM and not raw SQL you should not have to worry about SQL injection. If your using raw SQL in Django make sure to parameterize your user input. Consult Django's documentation for info on both the ORM and parameterization.

assistant: Django has you covered here.
Never ever insert raw user input into your SQL queries. Always use query parameters, and Django makes this very easy:
User.objects.filter(username=username)  # Dangerous!

User.objects.filter(username=username)  # Safe, username is a parameter

So in your view:
User.objects.get(username=request.POST['username'])  # Dangerous
User.objects.get(username=request.POST.get('username'))  # Safe

Django will automatically escape the username and use it as a parameter in the SQL query, making it safe.
So in short: Always let Django construct the SQL query, and never insert raw user input. As long as you do that, you'll be safe from SQL injection.

prompter: What is the difference between request.POST['username] and request.POST.get('username')?

assistant: In Django, request.POST is a dictionary-like object that contains the data submitted in a form as part of a POST request. The data is stored as key-value pairs, where the keys are the names of the form fields and the values are the data submitted by the user.

The difference between request.POST['username'] and request.POST.get('username') is that the first one will raise a KeyError if the 'username' key is not present in the request.POST dictionary, while the second one will return None or a default value if the key is not present.

assistant: They are quite similar, but there is one key difference:

request.POST['username'] will throw a KeyError if the username key is missing from the POST data.
request.POST.get('username') will simply return None if the key is missing, and won't throw an error.

So request.POST.get('username') is a safer choice if the username field is optional, or may be missing for some reason.
It's generally a good idea to use request.POST.get() to retrieve form data, to avoid potential KeyError exceptions being thrown.

prompter: Is there any performance difference between these two methods?

assistant: The difference between request.POST['username] and request.POST.get('username') is that the former is used to access the value of the 'username' key from the request.POST dictionary, while the latter is used to safely retrieve the value of the 'username' key, with an optional default value if the key is not found in the request.POST dictionary. If the key is not present, the former will raise a KeyError, while the latter will not.