Schemas - BackAnt

BackAnt uses marshmallow for request body validation. Schemas live in api/schemas/ and are used in the service layer to validate incoming data before processing.

Schema structure

Each schema is a marshmallow Schema subclass. The naming convention is Post<Name>Schema for POST request schemas:

# api/schemas/PostUsers_schema.py
from marshmallow import fields, Schema

class PostUsersSchema(Schema):
    name = fields.String(required=True)
    email = fields.Email(required=True)
    age = fields.Integer(load_default=None)

Using a schema in a service

from marshmallow import ValidationError
from schemas.PostUsers_schema import PostUsersSchema
from helper.functions.validation_error import validation_error

class UsersService:
    def create_user(self, data):
        try:
            validated = PostUsersSchema().load(data or {})
        except ValidationError as e:
            raise validation_error(e)

        return self.users_repository.add_user(**validated)

validation_error() is a helper in api/helper/functions/validation_error.py that converts a marshmallow ValidationError into an APIException(400) automatically.

Common field types

Field	Description
`fields.String()`	String value
`fields.Integer()`	Integer value
`fields.Float()`	Float value
`fields.Boolean()`	Boolean value
`fields.Email()`	Validates email format
`fields.URL()`	Validates URL format
`fields.List(fields.String())`	List of strings
`fields.Dict()`	Arbitrary dict
`fields.DateTime()`	ISO 8601 datetime string

Field options

Option	Description
`required=True`	Field must be present in input
`load_default=value`	Default value when field is missing
`allow_none=True`	Allow `null` values
`validate=`	Attach a validator function

Validation example

from marshmallow import fields, Schema, validate

class PostProductSchema(Schema):
    name = fields.String(required=True, validate=validate.Length(min=1, max=100))
    price = fields.Float(required=True, validate=validate.Range(min=0))
    stock = fields.Integer(load_default=0)

Nested schemas

class AddressSchema(Schema):
    street = fields.String(required=True)
    city = fields.String(required=True)

class PostUserSchema(Schema):
    name = fields.String(required=True)
    address = fields.Nested(AddressSchema, required=True)

Error format

When validation fails, validation_error() raises APIException(400). The response body will be:

{"message": "Ocurrió un error"}

For more detailed validation error messages, inspect error.messages in the ValidationError and pass them to APIException:

except ValidationError as e:
    raise APIException(status_code=400, message=str(e.messages))

​Schema structure

​Using a schema in a service

​Common field types

​Field options

​Validation example

​Nested schemas

​Error format