What exactly is the attribute in marshmallow.fields.Nested() function?

user_13232582 0
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I am trying to nest a Schema inside another Schema like the following:

class RecipePaginationSchema(PaginationSchema):
    data = fields.Nested(RecipeSchema, attribute = "items", many = True)

The result should look something like this: 

{
    "links": {
        "first": "http://localhost:5000/users/name/recipes?per_page=2&visibility=all&page=1",
        "last": "http://localhost:5000/users/name/recipes?per_page=2&visibility=all&page=2",
        "next": "http://localhost:5000/users/name/recipes?per_page=2&visibility=all&page=2"
    },
    "page": 1,
    "pages": 2,
    "per_page": 2,
    "total": 3,
    "data": [
        {
            "id": 11,
            ...
        }
}

However, when I tried to use another attribute instead of "items", I didn't get the "data" part in the JSON response. So, what exactly is this attribute thing referring to?

By the way, I'm following Packt's Python API Development Fundamentals book.

marshmallow flask schema python json
1 Answers

From the documentation:

attribute – The name of the attribute to get the value from when serializing. If None, assumes the attribute has the same name as the field. Note: This should only be used for very specific use cases such as outputting multiple fields for a single attribute. In most cases, you should use data_key instead.

In other words, you map your field 'data' in the RecipePaginationSchema to the attribute 'items' in the RecipeSchema.

I don't know your use case, but as explained in the documentation, you should use the attribute keyword as a last resort. Many use cases can be solved with the 'only' and 'exclude' keywords (see here).

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