Marshmallow custom validation message for email

Question

I use the following schema to validate data:

class UserSchema(db_schema.Schema):
    email = data_fields.Email(required = True, 
    error_messages={
          'required': 'Email is mandatory field.', 
          'type': 'The manager email is not valid.'
    })

But the ValidationError.messages.items has the following message:

 "Not a valid email address."

How to make it show my custom message? Is there anywhere a comprehensive list of possible values for error_messages dictionary because I suspect I will need to override other messages too.

Answer 1

I found the error_messages dictionary is wrong, the key should be "invalid":

class UserSchema(db_schema.Schema):
    email = data_fields.Email(required = True, 
    error_messages={
          'required': 'Email is mandatory field.', 
          'invalid': 'The manager email is not valid.'
    })

Answer 2

take a look at https://github.com/marshmallow-code/marshmallow/blob/dev/src/marshmallow/fields.py

The Field class defines "required", "null" and "validator_failed"

class Field(FieldABC):
     ...
     default_error_messages = {
            "required": "Missing data for required field.",
            "null": "Field may not be null.",
            "validator_failed": "Invalid value.",
        }
     ...

Specific field implementations inherit those messages and may extend the list. e.g. Email defines the additional error message "invalid"

class Email(String):
    ...
    default_error_messages = {"invalid": "Not a valid email address."}
    ...

Note: It looks like Email and other fields would overwirte the default_error_messages (instead of extending them) but actually the error messages are "collected" exlicit including parent classes

class Field(FieldABC):
    ...
    # Collect default error message from self and parent classes
    messages = {}  # type: typing.Dict[str, str]
    for cls in reversed(self.__class__.__mro__):
        messages.update(getattr(cls, "default_error_messages", {}))
    messages.update(error_messages or {})
    self.error_messages = messages
    ...

Answer 3

error_messages = {
    'required': 'Missing data for required field.',
    'null': 'Field may not be null.',
    'validator_failed': 'Invalid value.',
} 

you are doing correct but the key to be used is "validator_failed". This will override the default error message when validation failed!

Answer 4

error_messages = {
            "required": "Missing data for required field.", #You can change
            "null": "Field may not be null.", #You can change
            "validator_failed": "Invalid value.", #You can change
            "invalid": "It's not a valid email." #You can change
        } 

Just remove "default_" from the beginning of the var and you can custom any error message you like it.