Validate list in marshmallow

Question

currently I am using marshmallow schema to validate the request, and I have this a list and I need to validate the content of it.

class PostValidationSchema(Schema):
    checks = fields.List(
        fields.String(required=True)
    )

the checks field is a list it should only contain these specific values ["booking", "reservation", "flight"]

Answer 1

If you mean to check the list only has those three elements in that order, then use Equal validator.

from marshmallow import Schema, fields, validate


class PostValidationSchema(Schema):
    checks = fields.List(
        fields.String(required=True),
        validate=validate.Equal(["booking", "reservation", "flight"])
    )

schema = PostValidationSchema()

schema.load({"checks": ["booking", "reservation", "flight"]})  # OK
schema.load({"checks": ["booking", "reservation"]})  # ValidationError

If the list can have any number of elements and those can only be one of those three specific values, then use OneOf validator.

from marshmallow import Schema, fields, validate


class PostValidationSchema(Schema):
    checks = fields.List(
        fields.String(
            required=True,
            validate=validate.OneOf(["booking", "reservation", "flight"])
        ),
    )

schema = PostValidationSchema()

schema.load({"checks": ["booking", "reservation", "flight"]})  # OK
schema.load({"checks": ["booking", "reservation"]})  # OK
schema.load({"checks": ["booking", "dummy"]})  # ValidationError

Answer 2

In addition to Jerome answer, I also figured out that if you need to do something which requires more logic you could do:

def validate_check(check: str):
  return check in ["booking", "reservation", "flight"]

class PostValidationSchema(Schema):
    checks = fields.List(
        fields.String(required=True, validate=validate_check)
    )

Or using lambda:

class PostValidationSchema(Schema):
    checks = fields.List(
        fields.String(required=True, validate=lambda check: check in ["booking", "reservation", "flight"])
    )