Question

这是我的代码

conn_string = "dbname=detector user=postgres password=1234 host=localhost port=5432"
print "Connecting to database\n    ->%s" % (conn_string)     
# get a connection, if a connect cannot be made an exception will be raised here
conn = psycopg2.connect(conn_string)

正在输出这个，这似乎没问题。

Connecting to database
    ->dbname=detector user=postgres password=1234 host=localhost port=5432

我将此连接用作function(data, conn)。现在，我注意到测试命令的奇怪输出：

_measurement_id = cursor.execute(
    'SELECT measurement_id FROM measurements ORDER BY time desc limit 1;'
);

通过Python返回None但在psql内，我得到一个整数。我认为错误在于不使用try-catch - 除了创建连接。

如果这是问题，我如何将PostgreSQL连接传递给Python中的函数？

Answer 1

cursor.execute不会返回任何内容。执行查询后，您需要使用cursor.fetchone，cursor.fetchall或for row in cursor:来检索结果。

cursor.execute("...")
_measurement_id = cursor.fetchone()

它与异常处理无关。

Answer 2

尝试这样做

try:
    cursor.execute(
    'SELECT measurement_id FROM measurements ORDER BY time desc limit 1;')
    _measurement_id = cursor.fetchone()
except psycopg2.Error as e:
    pass
finally:
    cursor.close()

使用Python中的PostgreSQL执行返回None

2 个答案: