Validators

Validators are a vital part of any data validation library. Oblate, apart from providing built-in validation features, also provides the ability of writing custom validators.

This is done using the validate.field() function:

import oblate
from oblate import validate, fields

class User(oblate.Schema):
    id = fields.Integer()
    username = fields.String()
    is_employee = fields.Boolean(default=False)

    @validate.field(id)
    def validate_id_range(self, value, ctx):
        assert value >= 1000 and value <= 9999, 'Value must be in range 1000-9999 inclusive'

Initializing the schema with invalid data:

User({'id': 340})

causes the following error:

oblate.exceptions.ValidationError:
│
│ 2 validation errors in schema 'User'
│
└── In field id:
    └── Value must be in range 1000-9999 inclusive
│
└── In field username:
    └── This field is required.

Pre-built Validators

Some validators that are commonly used in various cases are preshipped by Oblate so you don’t have to implement such validations yourself. These validators are provided by the oblate.validate module.

For example, the range validator that we implemented above can be replaced with the one already provided by the library:

class User(oblate.Schema):
    id = fields.Integer(validators=[validate.Range(1000, 9999)])
    username = fields.String()
    is_employee = fields.Boolean(default=False)

The validators parameter takes a sequence of validate.Validator objects.

It is recommended to use the pre-defined validators whenever possible as they are tailored to be robust and flexible to suit most use cases.

These validators are documented in Validators API Reference.