Question

I have been struggling with this for hours and I feel like crying now as I’m unable to fathom out what is happening.

Here is a simplified version of my data:

mydata = [ { 'id': 123, 'thing': 'ghi', 'value': 1 }, { 'id': 456, 'thing': 'xyz', 'value': 0 } ]

This is the code I have:

import MySQLdb as mdb

con = None
con = mdb.connect('localhost', 'testing', 'anothervalue', 'andanother');
cur = con.cursor()

sql = "INSERT INTO `tablename` ( `id`, `thing`, `value` ) VALUES ( %(id)s, %(thing)s, %(value)s )"
cur.executemany( sql, ( mine for mine in mydata ) )
con.close()

What I expected to happen was that 2 rows would be inserted into tablename. What actually happens is that the script executes without any errors and no rows are inserted.

What am I doing wrong? If I do a single INSERT by hand it inserts into the table properly so I think know its not a problem with the MySQL database but rather how I’m passing the variables into the database.

An additional question I have is how to I insert value as a float? At the moment I have the definition of value in the table as TINYTEXT NOT NULL, I would like this to be FLOAT NOT NULL but I’m not sure how to handle the substition above.

Answer 1

There is no need to use a generator to loop over mydata. Just pass in mydata directly:

cur.executemany(sql, mydata)

The database adapter will loop over mydata for you and a generator expression only inserts a needless extra loop.

If you do not get any error messages but there are no changes either, check the following:

• Make sure you commit the transaction; run con.commit() after the .executemany() call.

• Tripple-check that mydata is not empty.

The database adapter will correctly handle float values for you; if a column is marked as FLOAT NOT NULL and you pass in a Python float value for that column, Things Just Work. That’s what SQL parameters are for, handling quoting of different datatypes correctly.