Plotly Dash回调错误：从数据库拉取数据时K线图无法显示

首次使用Plotly Dash实现股票K线图可视化，从CSV拉取数据时图表正常运行，但从SQLite数据库拉取数据时出现回调错误（Call Back Error: updating graph.figure），图表无法正常显示。

用户代码如下：

from dash import Dash, dcc, html, Input, Output
import plotly.graph_objects as go
import pandas as pd


app = Dash(__name__)

conn = sqlite3.connect('stocks.db')
cursor = conn.cursor()


app.layout = html.Div([
    html.H4('Apple stock candlestick chart'),
    dcc.Checklist(
        id='toggle-rangeslider',
        options=[{'label': 'Include Rangeslider',
                  'value': 'slider'}],
        value=['slider']
    ),
    dcc.Graph(id="graph"),
])


@app.callback(
    Output("graph", "figure"),
    Input("toggle-rangeslider", "value"))
def display_candlestick(value):
    
    cursor = conn.cursor()
    df = pd.read_sql("SELECT Datetime, Open, High, Low, Close FROM stock_data WHERE Symbol = ?", conn, params=('AAPL',))   


    fig = go.Figure(go.Candlestick(
        x=df['Datetime'],
        open=df['Open'],
        high=df['High'],
        low=df['Low'],
        close=df['Close']
    ))
    fig.update_layout(
        xaxis_rangeslider_visible='slider' in value
    )

    return fig

app.run_server(debug=True)

• 1. 补全缺失的依赖导入
  代码中未导入sqlite3库，这是数据库连接失败的直接原因，在代码开头添加：

  import sqlite3
  

• 2. 修正数据格式问题

  • 数据库中Datetime字段可能存储为字符串，需转换为Pandas可识别的日期类型，在读取数据后添加：

    df['Datetime'] = pd.to_datetime(df['Datetime'])
    

  • 检查Open/High/Low/Close字段是否为数值类型，若为字符串需转换：

    df[['Open', 'High', 'Low', 'Close']] = df[['Open', 'High', 'Low', 'Close']].astype(float)
    

• 3. 优化数据库连接逻辑
  回调函数内无需重复创建cursor，pd.read_sql可直接使用已建立的conn，移除冗余的cursor = conn.cursor()语句。

• 4. 添加异常捕获定位错误
  在回调函数中加入异常捕获，便于查看具体错误信息，避免应用崩溃：

  @app.callback(
      Output("graph", "figure"),
      Input("toggle-rangeslider", "value"))
  def display_candlestick(value):
      try:
          df = pd.read_sql("SELECT Datetime, Open, High, Low, Close FROM stock_data WHERE Symbol = ?", conn, params=('AAPL',))
          df['Datetime'] = pd.to_datetime(df['Datetime'])
          df[['Open', 'High', 'Low', 'Close']] = df[['Open', 'High', 'Low', 'Close']].astype(float)
          
          fig = go.Figure(go.Candlestick(
              x=df['Datetime'],
              open=df['Open'],
              high=df['High'],
              low=df['Low'],
              close=df['Close']
          ))
          fig.update_layout(
              xaxis_rangeslider_visible='slider' in value
          )
          return fig
      except Exception as e:
          print(f"回调错误详情: {str(e)}")
          return go.Figure()
  

内容的提问来源于stack exchange，提问作者Pravin