How to "edit" a step variable ?

Romain Lejeune

I have a workflow where every time a button is clicked, it'll compute a new result and append it to a list 'points' stored as a Class attribute under solution/.

The problem is that I can't set the 'points' list as a 'download' AND an 'upload' in a transaction where I could just append the 'points' like shown below, because I will have a cyclic dependency.

`class FirstStep(StepModel):
"""Step definition of the first step."""

visc: float = 0.04
dens: float = 998
speed: float = 32.5
bt_mrf: float = 0
bt_fusion: float = 0
points: list = [] 

@transaction(self=StepSpec(upload=["bt_mrf", "bt_fusion","points"], download=["visc", "dens","speed","points"]))
def calculate(self) -> None:
    """Method to compute the sum of two numbers."""
    self.bt_mrf, self.bt_fusion = calculate(self.visc,self.dens,self.speed)

    #round blend times to 3 decimal places
    self.bt_mrf=round(self.bt_mrf,3)
    self.bt_fusion=round(self.bt_fusion,3)

    temp_points=self.points
    temp_points.append((self.visc,self.dens,self.speed,self.bt_mrf,self.bt_fusion))
    self.points=temp_points 

`

Romain Lejeune

One way to handle this is to add another list in the Step definition and assign it in the callback in the page.py in the ui/

`class FirstStep(StepModel):
"""Step definition of the first step."""

visc: float = 0.04
dens: float = 998
speed: float = 32.5
bt_mrf: float = 0
bt_fusion: float = 0
points: list = []
points_current: list = []

@transaction(self=StepSpec(upload=["bt_mrf", "bt_fusion","points"], download=["visc", "dens","speed","points_current"]))
def calculate(self) -> None:
    """Method to compute the sum of two numbers."""
    self.bt_mrf, self.bt_fusion = calculate(self.visc,self.dens,self.speed)

    #round blend times to 3 decimal places
    self.bt_mrf=round(self.bt_mrf,3)
    self.bt_fusion=round(self.bt_fusion,3)

    temp_points=self.points_current
    temp_points.append((self.visc,self.dens,self.speed,self.bt_mrf,self.bt_fusion))
    self.points=temp_points
    #temp_points is used to avoid cyclic dependency

`

and in the ui:

`@callback(
Output("bt_mrf", "value"),
Output("bt_fusion", "value"),
Output("testing","children"),
Output("wait_completion", "children"),
Input("calc_button", "n_clicks"),
State("visc", "value"),
State("dens", "value"),
State("speed", "value"),
State("url", "pathname"),
prevent_initial_call=True,
)
def calculate(n_clicks, visc, dens, speed, pathname):
"""Callback function to trigger the computation."""
project = DashClient[Fusion_MixingSolution].get_project(pathname)
step = project.steps.first_step
step.visc = visc
step.dens = dens
step.speed = speed
step.calculate()
step.points_current=step.points

return step.bt_mrf, step.bt_fusion, str(step.points),True

`

This would work, but it seems a bit odd to me to have to handle that in the frontend somehow...
Any suggestion on another implementation ?

Thanks @Ryan OConnor for the use case!!