`modified_timestamp` 在 plotly store 组件中的用途是什么

Question

我正在阅读 https://dash.plot.ly/dash-core-components/store

上的第一个示例

为什么

@app.callback(Output('{}-clicks'.format(store), 'children'),
              [Input(store, 'modified_timestamp')],
              [State(store, 'data')])
def on_data(ts, data):
    if ts is None:
        raise PreventUpdate

    data = data or {}

    return data.get('clicks', 0)

而不是

@app.callback(Output('{}-clicks'.format(store), 'children'),
              [Input(store, 'data')])
def on_data(data):
    data = data or {}
    return data.get('clicks', 0)

我不明白为什么要使用 modified_timestamp。

Answer 1

来自您共享的文档页面：

Retrieving the initial store data

If you use the data prop as an output, you cannot get the initial data on load with the data prop. To counter this, you can use the modified_timestamp as Input and the data as State.

This limitation is due to the initial None callbacks blocking the true data callback in the request queue.

See https://github.com/plotly/dash-renderer/pull/81 for further discussion.

`modified_timestamp` 在 plotly store 组件中的用途是什么

what is `modified_timestamp` used for in plotly store component

store

plotly

plotly-dash