我正在用python和Dash编写程序，在其中我根据用户在下拉菜单中选择的数据更新图形。图形数据来自MySQL数据库，我有一个输入字段，用户可以在其中更改y-graph (id='max_value')
如果用户在最大输入字段中输入例如5，则一切顺利。如果用户写50，他首先输入5，则将调用“更新图形”功能，程序将从db中读取数据。在此操作完成之前，用户键入0，然后再次调用函数“ update graph”，并且程序尝试再次从db读取数据，而同时他仍从前一个函数中读取（写入5）。至少，我认为这是问题所在。
我知道更改最大值时不必读取数据，我可以编写一个用于更改最大值的新函数，但是还有其他方法可以解决此问题吗？一种互锁？
import mysql.connector
import pandas as pd
import dash
from dash.dependencies import Input, Output
import dash_core_components as dcc
import dash_html_components as html
import datetime
import plotly.graph_objs as go
app = dash.Dash()
#create mySQL connection
''' with ...'''
con = mysql.connector.connect(
host="*****",
user="*****",
passwd="*****",
database="*****",
)
print(con)
#read Id and name of EWon's
db_ewon = con.cursor()
db_ewon.execute("SELECT Id,name FROM esync_stations")
installations = db_ewon.fetchall()
installations_dict = {}
total_dict = {}
for item in installations:
# item[0]: installationID
# item[1]: name installation
#first we read all the parameters of the current installationID
parameters_dict = {}
db_parameters = con.cursor()
db_parameters.execute("SELECT Id,name FROM esync_tags WHERE stationID=%i" % item[0])
parameters = db_parameters.fetchall()
parameters_dict = {}
for par in parameters:
parameters_dict[par[0]] = par[1]
total_dict[item[0]] = parameters_dict
installations_dict[item[0]] = item[1]
#read Id and name from tag
db_tag = con.cursor()
db_tag.execute("SELECT Id,name FROM esync_tags WHERE stationID=10")
tags = db_tag.fetchall()
tags_dict = {}
for item in tags:
tags_dict[item[0]] = item[1]
# create layout
app.layout = html.Div(children=[
dcc.Input(id='max_value', value='100', type='text'),
html.Div(children='Select installation:'),
dcc.Dropdown(
id='dropdown-machine',
options=[{'label': machine, 'value': machineID} for machineID, machine in installations_dict.items()],
value=10
),
dcc.Dropdown(
id='dropdown-tag',
value=642
),
html.Div(id='output-graph'),
])
# update dropdown tags
@app.callback(
Output(component_id='dropdown-tag', component_property='options'),
[Input(component_id='dropdown-machine', component_property='value')]
)
def update_dropdown(input_data):
print('input data dropdown:', input_data)
# return [{'label': tag, 'value': tagID} for tagID, tag in tags_dict.items()]
return [{'label': tag, 'value': tagID} for tagID, tag in total_dict[input_data].items()]
# update graph
@app.callback(
Output(component_id='output-graph', component_property='children'),
[Input(component_id='dropdown-tag', component_property='value'),
Input(component_id='max_value', component_property='value')]
)
def update_graph(input_data, max):
print('input data graph:', input_data)
start = datetime.datetime(2015, 1, 1)
end = datetime.datetime.now()
print('before reading')
df = pd.read_sql_query('SELECT _date,Val FROM esync_tagshistory WHERE TagId=%i AND DATE(_date)>"2017-01-01"' % (int(input_data)), con)
print('after reading')
return dcc.Graph(
id='example-graph2',
figure={
'data': [
{'x': df._date, 'y': df.Val, 'type': 'line', 'name': input_data},
],
'layout': go.Layout(xaxis=dict(range=[start, end]),
yaxis=dict(range=[0, int(max)]),)
}
)
if __name__ == '__main__':
app.run_server(debug=True)
这是我收到的错误消息：
<mysql.connector.connection.MySQLConnection object at 0x0A9FBEF0>
* Serving Flask app "dash_graph_new" (lazy loading)
* Environment: production
WARNING: Do not use the development server in a production environment.
Use a production WSGI server instead.
* Debug mode: on
* Restarting with stat
<mysql.connector.connection.MySQLConnection object at 0x0A9FCFD0>
* Debugger is active!
* Debugger PIN: 413-847-908
* Running on http://127.0.0.1:8050/ (Press CTRL+C to quit)
127.0.0.1 - - [04/Dec/2018 12:37:57] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [04/Dec/2018 12:37:58] "GET /_dash-layout HTTP/1.1" 200 -
127.0.0.1 - - [04/Dec/2018 12:37:58] "GET /_dash-dependencies HTTP/1.1" 200 -
127.0.0.1 - - [04/Dec/2018 12:37:58] "GET /favicon.ico HTTP/1.1" 200 -
input data graph: 642
before reading
input data dropdown: 10
127.0.0.1 - - [04/Dec/2018 12:37:58] "POST /_dash-update-component HTTP/1.1" 200 -
after reading
127.0.0.1 - - [04/Dec/2018 12:38:01] "POST /_dash-update-component HTTP/1.1" 200 -
input data graph: 642
before reading
input data graph: 642
before reading
127.0.0.1 - - [04/Dec/2018 12:38:07] "POST /_dash-update-component HTTP/1.1" 500 -
Traceback (most recent call last):
File "C:\Python37\lib\site-packages\flask\app.py", line 2309, in __call__
return self.wsgi_app(environ, start_response)
File "C:\Python37\lib\site-packages\flask\app.py", line 2295, in wsgi_app
response = self.handle_exception(e)
File "C:\Python37\lib\site-packages\flask\app.py", line 1741, in handle_exception
reraise(exc_type, exc_value, tb)
File "C:\Python37\lib\site-packages\flask\_compat.py", line 35, in reraise
raise value
File "C:\Python37\lib\site-packages\flask\app.py", line 2292, in wsgi_app
response = self.full_dispatch_request()
File "C:\Python37\lib\site-packages\flask\app.py", line 1815, in full_dispatch_request
rv = self.handle_user_exception(e)
File "C:\Python37\lib\site-packages\flask\app.py", line 1718, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "C:\Python37\lib\site-packages\flask\_compat.py", line 35, in reraise
raise value
File "C:\Python37\lib\site-packages\flask\app.py", line 1813, in full_dispatch_request
rv = self.dispatch_request()
File "C:\Python37\lib\site-packages\flask\app.py", line 1799, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "C:\Python37\lib\site-packages\dash\dash.py", line 899, in dispatch
return self.callback_map[target_id]['callback'](*args)
File "C:\Python37\lib\site-packages\dash\dash.py", line 839, in add_context
output_value = func(*args, **kwargs)
File "C:\Users\Brecht\Documents\python_work\Display_graph\dash_graph_new.py", line 112, in update_graph
df = pd.read_sql_query('SELECT _date,Val FROM esync_tagshistory WHERE TagId=%i AND DATE(_date)>"2017-01-01"' % (int(input_data)), con)
File "C:\Python37\lib\site-packages\pandas\io\sql.py", line 314, in read_sql_query
parse_dates=parse_dates, chunksize=chunksize)
File "C:\Python37\lib\site-packages\pandas\io\sql.py", line 1413, in read_query
cursor = self.execute(*args)
File "C:\Python37\lib\site-packages\pandas\io\sql.py", line 1373, in execute
cur = self.con.cursor()
File "C:\Python37\lib\site-packages\mysql\connector\connection.py", line 813, in cursor
raise errors.OperationalError("MySQL Connection not available.")
mysql.connector.errors.OperationalError: MySQL Connection not available.