链式回调未在 Plotly Dash 应用程序中执行的问题

问：

我目前正在学习达世币中的链式回调，但停滞不前。有更多经验的人是否能够审查提供的代码并识别我可能犯的任何错误？

我的目标是链接回调，以便一个回调（使用该函数）的输出作为另一个回调的输入。但是，似乎没有执行任何回调。long_lasting_query()

import argparse

import dash_bootstrap_components as dbc
import pandas as pd
from dash import Dash, Input, Output, State, dcc, html
from dash.dash_table import DataTable


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        description="Dash example",
        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
    )

    parser.add_argument(
        "-a",
        "--addr",
        type=str,
        metavar="arg",
        required=True,
        help="address to bind to (ip:port)",
    )
    parser.add_argument("--debug", action="store_true", help="run in debug mode")

    args = parser.parse_args()

    return args


def long_lasting_query() -> pd.DataFrame:
    df = pd.read_csv(
        "https://raw.githubusercontent.com/plotly/datasets/master/gapminder_unfiltered.csv"
    )

    return df


columns = ["country", "continent", "year", "lifeExp", "pop", "gdpPercap"]

app = Dash(
    external_stylesheets=[dbc.themes.BOOTSTRAP], suppress_callback_exceptions=True
)

app.layout = dbc.Container(
    [
        html.P(
            "Year: ",
            style={"display": "inline-block", "margin-right": "8px"},
        ),
        dcc.Input(id="year", type="number", min=0),
        html.Button("Submit", id="submit-val", n_clicks=0),
        DataTable(
            columns=[{"name": c, "id": c} for c in columns],
            id="tbl",
            page_size=20,
            sort_action="native",
            style_header={
                "textAlign": "center",
            },
        ),
    ]
)


@app.callback(
    Output("db_data", "value"),
    Input("submit-val", "n_clicks"),
    State("year", "value"),
    prevent_initial_call=True,
)
def load_data(n_clicks, value):
    df = long_lasting_query()
    df = df[df["year"] == value]
    if df.empty:
        return "{}"

    return df.to_json(orient="split")


@app.callback(
    Output("tbl", "data"),
    Input("db_data", "value"),
)
def update_table(value):
    df = pd.read_json(value, orient="split")
    if df.empty:
        return "{}"

    return df.to_dict("records")


def main() -> None:
    args = parse_args()
    host, port = args.addr.split(":")
    app.run(host=host, port=port, debug=args.debug)


if __name__ == "__main__":
    main()

我希望获得已根据指定年份筛选的数据。