Flask mySQLDB execute success or failure

Question

I am new to Python-Flask and am trying to use MySQLDB to conenct to the database. However, I am unable to determine how to check if the query executed by the cursor is successful or if it failed. In the code below, can someone please advise how I can go about the condition in the if statement? c is a cursor to a database and it is connecting successfully, so I excluded it from the code below.

qry = "SELECT count(*) FROM users where username = (%s)" % (username)
try:
    x = c.execute(qry) #Is this correct? Doe execute command return a value?
    if <<*Check if the query executed successfully*>>:
        return 'Success'
    else:
        return 'Failure'
except Exception as e:
    return 'Failure'

This seems like an odd thing to want to do. You're asking for a count, so the normal behaviour would be to return the value, surely? — Daniel Roseman, Dec 22 '16 at 09:21
Thanks Daniel. It was just a sample query. imagine I misspelled the table name as "users" instead of "user"... or Imagine an insert query instead and I try to insert a blank username, and the DB has username as primary key. So, it would fail, and I am trying to capture in the return if the query execution is successful or not. — tirupats, Dec 22 '16 at 09:24

score 2 · Accepted Answer · answered Dec 22 '16 at 09:28

c.execute(qry) in your case won't return anything. So, You can't use it for if statement.

However, You could use fetchall() or fetchone() to check if there are some results for your query. It would look something like this:

qry = "SELECT count(*) FROM users where username = (%s)" % (username)
try:
    c.execute(qry) #Is this correct? Doe execute command return a value?
    user = c.fetchone()
    if user:
        return 'Success'
    else:
        return 'Failure'
except Exception as e:
    return 'Failure'

First, there will no be `fetchone`, if `insert` is to be used. Second, any error on `insert` will be catch with `except` part. — Fejs, Feb 13 '18 at 07:00

score 0 · Answer 2 · answered Dec 22 '16 at 09:23

You already have the means for detecting the failure in the code you have posted. If something goes wrong with the query, Python will raise an exception, which you can catch. Although it's worth noting that you should never catch a bare Exception, and you should certainly never hide what that exception is; catch the relevant MySQLdb exceptions, eg MySQLdb.Error.

Flask mySQLDB execute success or failure

2 Answers2