python中的sqlite查询仅使用对象将最后一行写入文件

Question

首先，在过去的几个月中，我是Python的新手，直到现在，它的运行情况还不错。 但是我很困惑，我非常想通过显示器砸一下头。

当我运行此脚本时，我只会将最后一行数据写入文件，而我需要的是所有数据行都将以类部分中的格式写入。

VOL_HOURS.db有多个行，但只有最后一行被写入。 这是我的脚本：

    from vlist import VLIST

import sqlite3
import decimal
import os
import sys
import uuid

VERSION = "oops"
DEVICE_SOFTWARE_VERSION = "OOPS"
FILENAME = "VHOURS.txt"
conn = sqlite3.connect("VOL_HOURS.db")






def fromVolunteers():
    conn = sqlite3.connect("VOL_HOURS.db")


with conn:

    cur = conn.cursor()
    cur.execute("SELECT BOB, DAVE, CAROL, ANDY, CARL, DANNY, CHERYL, CYNTHIA, TARA, SCOTT, ASHLEY, CRYSTAL FROM VOLUNTEERS")
    rows = cur.fetchall()




for row in rows:
    bob = row[0] 
    dave = row[1]
    carol = row[2]
    andy= row[3]
    carl = row[4]
    danny = row [5]
    cheryl = row [6]
    cynthia = row [7]
    tara = row [8]
    scott = row [9]
    ashley = row [10]
    crystal = row [11]



def main():
    fromVolunteers()
    testOutput = open(FILENAME, "w+")

    vlist = VLIST()
    vlist.setBob(bob)
    vlist.setDave(dave)
    vlist.setCarol(carol)
    vlist.setAndy(andy)
    vlist.setCarl(carl)
    vlist.setDanny(danny)
    vlist.setCheryl(cheryl)
    vlist.setCynthia(cynthia)
    vlist.setTara(tara)
    vlist.setScott(scott)
    vlist.setAshley(ashley)
    vlist.setCrystal(crystal)

    vlist.dump_object(testOutput)

    testOutput.flush()
    testOutput.close()
cur.close()
conn.close()

if __name__ == "__main__":
    sys.exit(main())

它从中提取的类文件是：

class VLIST:

    def __init__(self):
        self.bob = ""
        self.dave = ""
        self.carol = ""
        self.andy = ""
        self.carl = ""
        self.danny = ""
        self.cheryl = ""
        self.cynthia = ""
        self.tara = ""
        self.scott = ""
        self.ashley = ""
        self.crystal = ""

    def setBob(self,bob):
        self.bob = bob
        return

    def setDave(self,dave):
        self.dave = dave
        return

    def setCarol(self,carol):
        self.carol = carol
        return

    def setAndy(self,andy):
        self.andy = andy
        return

    def setCarl(self,carl):
        self.carl = carl
        return

    def setDanny(self,danny):
        self.danny = danny
        return

    def setCheryl(self,cheryl):
        self.cheryl = cheryl
        return

    def setCynthia(self,cynthia):
        self.cynthia = cynthia
        return

    def setTara(self,tara):
        self.tara = tara
        return

    def setScott(self,scott):
        self.scott = scott
        return

    def setAshley(self,ashley):
        self.ashley = ashley
        return

    def setCrystal(self,crystal):
        self.crystal = crystal
        return

    def dump_object(self,testOutput):
        testOutput.write("VLIST,"+self.bob+","+self.dave+","+self.carol+","+self.andy+","+self.carl+","+self.danny+","+self.cheryl+","+self.cynthia+","+self.tara+","+self.scott+","+self.ashley+","+self.crystal+","+"\n")

如果这令人困惑，我会提前道歉，就像我说过的那样。 感谢您的时间。

Answer 1

在for row in rows:迭代for row in rows:您只是覆盖了变量bob ， dave等的先前值。因此，在迭代结束时，这些变量只有最后一个值。

从fromVolunteers()删除迭代。 此函数应仅设置rows变量，并将迭代放在main函数中：

import sqlite3
import decimal
import os
import sys
import uuid

VERSION = "oops"
DEVICE_SOFTWARE_VERSION = "OOPS"
FILENAME = "VHOURS.txt"
conn = sqlite3.connect("VOL_HOURS.db")

def fromVolunteers():
    conn = sqlite3.connect("VOL_HOURS.db")

    with conn:
        cur = conn.cursor()
        cur.execute("SELECT BOB, DAVE, CAROL, ANDY, CARL, DANNY, CHERYL, CYNTHIA, TARA, SCOTT, ASHLEY, CRYSTAL FROM VOLUNTEERS")
        rows = cur.fetchall()
def main():
    fromVolunteers()
    testOutput = open(FILENAME, "w+")

    for row in rows:
        vlist = VLIST()
        vlist.setBob(row[0])
        vlist.setDave(row[1])
        vlist.setCarol(row[2])
        vlist.setAndy(row[3])
        vlist.setCarl(row[4])
        vlist.setDanny(row[5])
        vlist.setCheryl(row[6])
        vlist.setCynthia(row[7])
        vlist.setTara(row[8])
        vlist.setScott(row[9])
        vlist.setAshley(row[10])
        vlist.setCrystal(row[11])
        vlist.dump_object(testOutput)

testOutput.flush()
testOutput.close()
cur.close()
conn.close()

Answer 2

这是代码的重构版本。 不知道您的数据库模式，数据库内容或要测试的示例文件，这只是您可以做的近似。 随着VOLUNTEERS表继续添加或删除列，您只需要更改代码顶部的COLUMNS元组即可补偿COLUMNS的更改。

import contextlib
import sqlite3


DATABASE = 'VOL_HOURS.db'
OUTPUT = 'VHOURS.nmf'
COLUMNS = ('BOB', 'DAVE', 'CAROL', 'ANDY', 'CARL', 'DANNY', 'CHERYL',
           'CYNTHIA', 'TARA', 'SCOTT', 'ASHLEY', 'CRYSTAL')


def main():
    with open(OUTPUT, 'w') as file:
        for row in from_volunteers():
            file.write(str(VolunteerList.new(row)))


def from_volunteers():
    with sqlite3.connect(DATABASE) as connection:
        with contextlib.closing(connection.cursor()) as cursor:
            query = 'SELECT {} FROM VOLUNTEERS'.format(', '.join(COLUMNS))
            cursor.execute(query)
            return cursor.fetchall()


class VolunteerList:

    @classmethod
    def new(cls, row):
        obj = cls()
        for key, value in zip(COLUMNS, row):
            obj[key] = value
        return obj

    def __init__(self):
        self.__data = [''] * len(COLUMNS)

    def __setitem__(self, key, value):
        self.__data[COLUMNS.index(key.upper())] = value

    def __str__(self):
        return ','.join(['VLIST'] + self.__data + ['\n'])


if __name__ == '__main__':
    main()