In docs, DelimitedList field doesn't produce the expected query parameter format

[pamelafox]

I am using the DelimitedList field like so:

class PieChartParams(Schema):
    title = String(required=False, validate=Length(0, 30))
    values = DelimitedList(Number(validate=Range(min=0, max=3.4028235e38)), required=True)
    labels = DelimitedList(String)

And I am using it for the query parameters:

@app.get("/charts/pie")
@app.input(PieChartParams, location="query")
@app.output(ImageOutSchema, content_type='image/png')
def pie_chart(data: dict):
    fig = Figure()
    axes: Axes = fig.add_subplot()
    axes.pie(data["values"], labels=data.get("labels"))
    axes.set_title(data.get("title"))
    return send_figure_as_png(fig)

That field lets me send a query like so:

charts/pie?title=Enrolled%20students&labels=C,Ruby,Java,Python&values=10,20,15,30.5

However, if I enable the APIFlask docs and add multiple values to the DelimitedList fields, the generated URL is instead like this:

charts/pie?title=Enrolled%2520students&values=10&values=20&values=30&values=15&labels=C&labels=Ruby&labels=Java&labels=Python

That query parameter is repeating the fields instead of putting them as comma separated values. That isn't what the parser expects, apparently, as the values and labels come in to APIFlask as lists with single values (the first of each parameter).

For full code, see:
https://github.com/pamelafox/flask-charts-api-container-app/blob/main/src/api/__init__.py

Environment:

• Python version: 3.11
• Flask version: 2.2.3
• APIFlask version: 1.3.0

Docs screenshot here:

[tkzt]

@pamelafox Hi there. After some source code reading, I found the query parameters generating behavior above is a default behavior to List field in marshmallow, which seems can't be customized even though there are many parameter serializing ways.

Hope it helpful to you :/

[greyli]

Thanks tkzt for the explanation. After some investigation, I think it needs to be fixed in apispec. It shouldn't set the param explode option to true. Instead, it should set the correct param style and explode for DelimitedList. At least, the explode and style should be allowed to pass in the Field(metadata={}).

I will try to create an issue/PR to apispec later. Moved this issue to the 2.1.0 milestone.

Ref:

• Function to parse list field: https://github.com/marshmallow-code/apispec/blob/2392b2eae6b6d3a12345201fd86d78c779755650/src/apispec/ext/marshmallow/openapi.py#L223
• Allowed property list: https://github.com/marshmallow-code/apispec/blob/2392b2eae6b6d3a12345201fd86d78c779755650/src/apispec/ext/marshmallow/field_converter.py#L45