Validators in Flask

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Learn to use validators in Flask to maintain data integrity in your databases by defining validation rules for user input

beginner Published 30 Jun 2023

Action Steps

Define a model using Flask's db.Model and SerializerMixin
Use the @validates decorator to specify the field to be validated, e.g. 'username'
Create a validation function, e.g. validate_username, to check the input value
Raise a ValueError if the input is invalid, e.g. empty string
Return the validated value if it passes the check

Who Needs to Know This

Backend developers and beginners can benefit from this lesson to ensure data consistency and security in their Flask applications

Key Insight

💡 Validators help maintain data integrity by checking user input against predefined rules

Key Takeaways

Learn to use validators in Flask to maintain data integrity in your databases by defining validation rules for user input

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Title: Validators in Flask

URL Source: https://dev.to/elifrie/validators-in-flask-5fo1

Published Time: 2023-06-30T15:31:23Z

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Posted on Jun 30, 2023

# Validators in Flask

[#flask](https://dev.to/t/flask)[#backend](https://dev.to/t/backend)[#beginners](https://dev.to/t/beginners)

As you begin to create and manage databases it's important to keep in mind that the type of data you are allowing users to input can have large effects on your databases. Validators are used to do just that; maintain the integrity of the data flowing into your databases.

You must imagine every possible edge case for how a user will interact with your webpage and then utilize validators to protect against those cases.

Using validators is generally very intuitive and basic.

Within your models and class definitions on the back-end you can define validators as so:

```
class User(db.Model, SerializerMixin):
__tablename__ = 'users'

##here all your relationships will lie##

###below you are defining what variable you will be validating.##
@validates('username'):
##creating a validation##
def validate_username(self, key, value):
if not value:
raise ValueError('Please enter a username')
##forcing a user to enter a value for their username to proceed, otherwise they will see a value error##
return value
##returning the value if a username is provided by the user##
```

Above is an example of how you

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Validators in Flask

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