Is it possible to validate list using marshmallow?

python marshmallow
avasin picture avasin · May 15, 2016 · Viewed 26.7k times · Source

Is it possible to validate list using marshmallow?

class SimpleListInput(Schema):
    items = fields.List(fields.String(), required=True)

# expected invalid type error
data, errors = SimpleListInput().load({'some': 'value'})

# should be ok 
data, errors = SimpleListInput().load(['some', 'value'])

Or it is expected to validate only objects?

Answer

Maxim Kulkin picture Maxim Kulkin · Dec 1, 2016

To validate top-level lists, you need to instantiate your list item schema with many=True argument.

Example:

class UserSchema(marshmallow.Schema):
    name = marshmallow.fields.String()

data, errors = UserSchema(many=True).load([
    {'name': 'John Doe'},
    {'name': 'Jane Doe'}
])

But it still needs to be an object schema, Marshmallow does not support using top-level non-object lists. In case you need to validate top-level list of non-object types, a workaround would be to define a schema with one List field of your types and just wrap payload as if it was an object:

class SimpleListInput(marshmallow.Schema):
    items = marshmallow.fields.List(marshmallow.fields.String(), required=True)

payload = ['foo', 'bar']
data, errors = SimpleListInput().load({'items': payload})

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