数据库访问生成器功能是否有优势？

Question

与仅.fetchone()在while循环中调用相比，编写以下生成器函数是否有优势？如果是这样，那优势是什么？

谢谢。

def testf2():
    db = connectToMysqlDB(None)

    sql_statement = " ".join([
        "select d.* ",
        "from dr_snapshot d ",
        "order by d.PremiseID asc, d.last_read asc; "])

    sel_cur = db.cursor()
    rc = sel_cur.execute(sql_statement)

    loop_ok = True
    while loop_ok:
        meter_row = sel_cur.fetchone()
        if meter_row:
            yield meter_row
        else:
            loop_ok = False

    yield None

for read_val in testf2():
   print(read_val)
   #Perform something useful other than print.

('610159000', 6, datetime.datetime(2012, 7, 25, 23, 0), 431900L, 80598726L)
('610160000', 6, datetime.datetime(2012, 7, 25, 23, 0), 101200L, 80581200L)
None

Answer 1

不。从功能上讲，它们是相同的，但是，如果您想重用代码，则将其包装在生成器中是有好处的。例如，您可以添加代码以在读取生成器块后关闭连接/光标。我建议您将此代码添加到上面的代码中，以便关闭游标。

def testf2():
    try:
        db = connectToMysqlDB(None)

        sql_statement = " ".join([
            "select d.* ",
            "from dr_snapshot d ",
            "order by d.PremiseID asc, d.last_read asc; "])

        sel_cur = db.cursor()
        rc = sel_cur.execute(sql_statement)

        loop_ok = True
        while loop_ok:
            meter_row = sel_cur.fetchone()
            if meter_row:
                yield meter_row
            else:
                loop_ok = False
    except ProgrammingError:
        print "Tried to read a cursor after it was already closed"
    finally:
        sel_cur.close()

这将使重用变得更容易，因为您只需要在一个地方正确地进行连接管理即可。