Question

我正在尝试使用以下代码查询和获取数据库的最后一行：

from flask import Flask, render_template, redirect, url_for
from flask_bootstrap import Bootstrap
from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, BooleanField
from wtforms.validators import InputRequired, Email, Length
from flask_sqlalchemy  import SQLAlchemy
from werkzeug.security import generate_password_hash, check_password_hash
from flask_login import LoginManager, UserMixin, login_user, login_required, logout_user, current_user
import json

app = Flask(__name__)
app.config['SECRET_KEY'] = 'removed'
app.config['SQLALCHEMY_DATABASE_URI'] = "mysql+mysqlconnector://{username}:{password}@{hostname}/{databasename}".format(
    username="removed",
    password="removed",
    hostname="removed",
    databasename="removed",
)   #used to use sqlite here so potential for errors...
app.config["SQLALCHEMY_POOL_RECYCLE"] = 299 #do i need this line and below line???
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
bootstrap = Bootstrap(app)
db = SQLAlchemy(app)
login_manager = LoginManager()
login_manager.init_app(app)
login_manager.login_view = 'login'

class temperaturelog(db.Model):
    TemperatureID = db.Column(db.Integer, primary_key=True)
    Temperature = db.Column(db.Float(5))
    dTime = db.Column(db.DateTime) #check the actual data types here

    def __init__(self, TemperatureID, Temperature, dTime):
        self.TemperatureID = TemperatureID
        self.Temperature = Temperature
        self.dTime = dTime

    def __repr__(self):
        return '%r' % self.Temperature

def getTemperatureData():
    #need to convert this query into sqlalchemy queries "SELECT * FROM readings ORDER BY ID DESC LIMIT 1";
    #need to connect/use the right table below
    #data = jsonify(temperaturelog.query.order_by(temperaturelog.dTime.desc()).first())
    datalist = {}
    data = temperaturelog.query.order_by(temperaturelog.TemperatureID.desc()).first()
    data = data.Temperature
    datalist["temperature"] = data
    datalist["datetime"] = "12-12-12 23-23-23"
    datalist = json.dumps(datalist)
    return datalist

这里我连接到一个在线数据库（我使用pythonanywhere来托管这一切）我需要数据库中的最后一行数据我相信通常的SQL命令是：

"SELECT * FROM readings ORDER BY ID DESC LIMIT 1";

当我使用下面的代码尝试检索dTime值以进行进一步处理时，它会抛出错误对象＆＃39; float＆＃39;没有属性.dTime，因此我的查询只是返回温度，如何让查询返回整个最后一行，以便我可以使用.Temperature和.dTime来访问特定值？

data2 = data.dTime
datalist["datetime"] = data2

Answer 1

在getTemperatureData()中，您首先使用data变量存储查询结果集：

data = temperaturelog.query.order_by(temperaturelog.TemperatureID.desc()).first()

在下一行中，用温度覆盖data（可能是浮点数）：

data = data.Temperature

因此，下次尝试使用data时，它包含一个浮点而不是结果集。例如，将第二行中的变量重命名为data_temperature。

如何使用Flask MySQLAlchemy进行这个特定的SQL查询？

1 个答案: