使用pyodbc的python类.多行出现错误

Question

这段代码打印出一行预期的数据。它在第二行打印出"无"，我也想对此进行解释，但这不是的主要问题

rows = cursor.fetchone()
for row in rows:
cur = SHIPMENT_BO(row.SHIPMENT_NUM, row.SHIPMENT_ID, row.ORIGIN_BRANCH_CODE, row.DEST_BRANCH_CODE)
print(cur.PrintShipment())

此代码只返回函数中的第一个print语句，而不返回任何数据。

rows = cursor.fetchall()
for row in rows:
cur = SHIPMENT_BO(row.SHIPMENT_NUM, row.SHIPMENT_ID, row.ORIGIN_BRANCH_CODE, row.DEST_BRANCH_CODE)
print(cur.PrintShipment())

这是我在上面叫的班级

class SHIPMENT_BO:
def __init__(self, shipNo, shipId, origBranch, destBranch):
self.__shipmentNo = shipNo
self.__shipmentID = shipId
self.__originBranch = origBranch
self.__destinationBranch = destBranch

def PrintShipment(self):
print("Shipment No, Shipment ID, Origin Branch, Destination Branch")
print(self.__shipmentNo + " " + str(self.__shipmentID) + " " + self.__originBranch + " " + self.__destinationBranch)

如果我直接打印发货编号，它会按预期打印数百万行

rows = cursor.fetchall()
for row in rows:
print(row.SHIPMENT_NUM)
#cur = SHIPMENT_BO(row.SHIPMENT_NUM, row.SHIPMENT_ID, row.ORIGIN_BRANCH_CODE, row.DEST_BRANCH_CODE)
#print(cur.PrintShipment())

我的第一个问题是，为什么代码和类适用于一行而不适用于多行？我的第二个问题是，为什么在有一行的代码后面打印"无"？最后，这段代码根本不起作用(打印语句都不执行)，您肯定会在光标中至少得到一行所选的内容。

rows = cursor.fetchone()
for row in rows:
cur = SHIPMENT_BO(row.SHIPMENT_NUM, row.SHIPMENT_ID, row.ORIGIN_BRANCH_CODE, row.DEST_BRANCH_CODE)
print(cur.PrintShipment())

Answer 1

re：fetchone()与fetchall()

通过使用。。。

rows = cursor.fetchone()
for row in rows:

看起来您希望pyodbc的fetchone()方法返回一个列表，该列表包含所提取的一行的单个元组，但事实并非如此。它返回一个pyodbc.Row对象。当您迭代该对象时，实际上是在迭代该行的列值：

sql = """
SELECT 'foo' AS col1, 42 AS col2
"""
rows = cursor.execute(sql).fetchone()
for row in rows:
print(row)

将打印

foo
42

另一方面，fetchall()确实返回了一个(pyodbc.Row对象的)列表，所以它的行为更像您期望的

sql = """
SELECT 'foo' AS col1, 42 AS col2
UNION ALL
SELECT 'bar' AS col1, 123 AS col2
"""
rows = cursor.execute(sql).fetchall()
for row in rows:
print(row)

将打印

('foo', 42)
('bar', 123)

re：每行打印None

当你做

print(cur.PrintShipment())

您可以调用PrintShipment方法，该方法包括自己的print()函数调用，以显示列标题和列数据。然后，在PrintShipment方法返回后，您就是print，使用PrintShipment方法的返回值，即None，因为它不包括return语句。为了避免打印伪造的None值，只需调用方法本身：

cur.PrintShipment()  # not wrapped in a print() function