Accessing a computed Var in a Base object

[hpharmsen]

I have a state which contains a list of objects.
How do I access a computed var in one of these sub objects?

To illustrate I simplified my code to the bare minimum:

class Person(rx.Base):
name: str

@rx.var
def hello_name(self) -> str:
return "Hello " + self.name

class State(rx.State):
count: int = 5
persons: list[Person] = [Person(name='Alice'), Person(name='Bob')]

def index():
return rx.foreach(
State.persons,
lambda person: rx.html('<p>' + person.hello_name + '</p>')
)

When I substitute hello_name for just name it works fine.
Somehow I don't get the concept.

[picklelo]

@hpharmsen The @rx.var decorator only works within state classes (not within the a Base class as you have it here). You want to use the @property decorator that's builtin to Python instead.

It looks like Pydantic supports computed_fields from their v2.0 but We are still using 1.10 in Reflex.

Here's a way to do this currently by overriding the dict method to make sure the property gets serialized:

import reflex as rx

class Person(rx.Base):
    name: str

    @property
    def hello_name(self) -> str:
        return "Hello " + self.name

    def dict(self, **kwargs):
        return super().dict(**kwargs) | {"hello_name": self.hello_name}


class State(rx.State):
    count: int = 5
    persons: list[Person] = [Person(name="Alice"), Person(name="Bob")]


@rx.page()
def index():
    return rx.foreach(
        State.persons, lambda person: rx.html("<p>" + person.hello_name + "</p>")
    )

app = rx.App()

[hpharmsen]

Thank you Nikhil. That works!

I presume this is not how things are normally supposed to work in Reflex.
What would be the Reflex way of performing an operation on each element in a list which is part of the State?

[picklelo]

Normally the way you had it would work since each field in the class will get sent to the frontend. Pydantic doesn't by default send the @property tags down which is why we need this workaround. We can probably try to make this happen by default so you don't need to modify the dict method.

[hpharmsen]

Clear. Thank you!

[benedikt-bartscher]

Related to #2429, reflex could automatically serialize those properties without the dict workaround