使用sqlite的fetchone()读取循环中的第一行 [英] Read first row in loop using sqlite's fetchone()

问题描述

我正在使用循环获取fetchone()的内容，每次代码读取fetchone()时，光标就会移至下一行.我知道我需要小心.我正在使用在 https:中找到的示例: //dev.mysql.com/doc/connector-python/zh-CN/connector-python-api-mysqlcursor-fetchone.html 当我有多于一行的行时有效，但只有一行时会出现错误

I am using a loop to get the contents of fetchone(), every time code reads fetchone() the cursor moves to the next row. I understand that I need to be careful. I am using the example found here https://dev.mysql.com/doc/connector-python/en/connector-python-api-mysqlcursor-fetchone.html this works when I have more then one row but when there is a single row I get an error

    for k, v in cur.fetchone().items():
AttributeError: 'NoneType' object has no attribute 'items'

两个相关功能

def dict_factory(cursor, row):
    d = {}
    for idx, col in enumerate(cursor.description):
        d[col[0]] = row[idx]
    return d

def open_sql(sql_folder, sql_name, sql_table):
    # databases are located at /work/jmjohnso1/db_project  
    path_name = os.path.join(sql_folder,sql_name).strip()
    con = lite.connect(path_name)
    con.row_factory = dict_factory
    cur = con.cursor()
    cur.execute('SELECT * FROM ' + sql_table) 

    dict_contents = defaultdict(list) 

    for row in cur:
        for k, v in cur.fetchone().items():
            dict_contents[k].append(v)

    con.close()
    print(dict_contents)
    return dict_contents

如果您需要完整的代码:

In case you want the entire code:

# python3.5
# pymongo version 3.2.2
# MongoDB shell version: 3.0.11

import os
import pymongo
from pymongo import MongoClient
import sqlite3 as lite
import pyewf
import hashlib
from itertools import chain
from collections import defaultdict
import pprint

def list_sql_db(folder):
    # need a list for multiprocessing so I made a file. 
    file_name = os.path.join(folder, 'sql_db')
    if not os.path.isfile(file_name):
        with open (file_name, 'w') as line:
            for (dirpath, dirs, files) in os.walk(folder):
                for name in files:
                    line.write(name + '\n')
    return file_name    

def dict_factory(cursor, row):
    d = {}
    for idx, col in enumerate(cursor.description):
        d[col[0]] = row[idx]
    return d

def open_sql(sql_folder, sql_name, sql_table):
    # databases are located at /work/jmjohnso1/db_project  
    path_name = os.path.join(sql_folder,sql_name).strip()
    con = lite.connect(path_name)
    con.row_factory = dict_factory
    cur = con.cursor()
    cur.execute('SELECT * FROM ' + sql_table) 

    dict_contents = defaultdict(list) 

    for row in cur:
        for k, v in cur.fetchone().items():
            dict_contents[k].append(v)

    con.close()
    print(dict_contents)
    return dict_contents

def insert_tsk_mongo(sql_folder, sql_name, sql_table):
    client = MongoClient() # connect to mongodb
    db = client.nus # make or use a db called nus
    contents = open_sql(sql_folder, sql_name, sql_table)
    collection = sql_name.strip().replace('-','_') # because mongo will write but not read a collection with -

    # document_id = db[collection].insert({ # sql_name is the hard drive name 
        # sql_table:
            # contents           
    # })

###############################################################################

sql_folder = '/work/jmjohnso1/db_project'    
# sql_tables = ['tsk_fs_info', 'tsk_image_info',
              # 'tsk_db_info ', 'tsk_image_names',
              # 'tsk_file_layout', 'tsk_objects',
              # 'tsk_files', 'tsk_vs_info', 'tsk_vs_parts']

sql_tables = ['tsk_fs_info']              

sql_folder_name = list_sql_db(sql_folder)

with open (sql_folder_name, 'r') as read: 
    sql_names = read.readlines()

for sql_name in sql_names:
    for sql_table in sql_tables:
        insert_tsk_mongo(sql_folder, sql_name, sql_table)
    break    

推荐答案

您要获取行两次，一次是使用for row in cur:循环，然后是使用cur.fetchone()循环.在最后一行，要用完的行已用完，因此返回了None.

You are fetching rows twice, once with the for row in cur: loop, then in the loop with cur.fetchone(). At the last row, you have run out of rows to fetch, so None is returned.

已经游标游标时，不需要使用cur.fetchone().只需放下cur.fetchone()调用，并使用您已经通过for提取的行:

There is no need to use cur.fetchone() when you are already looping over the cursor. Just drop the cur.fetchone() call and use the row you already fetched with for:

for row in cur:
    for k, v in row.items():
        dict_contents[k].append(v)

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