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name

A PHP Error was encountered

Severity: Notice

Message: Undefined index: userid

Filename: views/question.php

Line Number: 191

Backtrace:

File: /home/prodcxja/public_html/questions/application/views/question.php
Line: 191
Function: _error_handler

File: /home/prodcxja/public_html/questions/application/controllers/Questions.php
Line: 433
Function: view

File: /home/prodcxja/public_html/questions/index.php
Line: 315
Function: require_once

I am using SQLAlchemy connection.execute(sql) to transform select results to array of maps. Have following code


def __sql_to_data(sql):
    result = []
    connection = engine.connect()
    try:
        rows = connection.execute(sql)
        for row in rows:
            result_row = {}
            for col in row.keys():
                result_row[str(col)] = str(row[col])
            result.append(result_row)
    finally:
        connection.close()
    return result

and e.g.

__sql_to_data(sql_get_scan_candidate)
gives me nice data structure (Of course I am using this for small data sets). But in order to add parameter to sql I am currently using format e.g.

return __sql_to_data(sql_get_profile.format(user_id))

Question How to modify procedure to make possible something like

return __sql_to_data(sql_get_profile,user_id)

The tutorial gives a pretty good example for this:

>>> from sqlalchemy.sql import text
>>> s = text(
...     "SELECT users.fullname || ', ' || addresses.email_address AS title "
...         "FROM users, addresses "
...         "WHERE users.id = addresses.user_id "
...         "AND users.name BETWEEN :x AND :y "
...         "AND (addresses.email_address LIKE :e1 "
...             "OR addresses.email_address LIKE :e2)")
SQL>>> conn.execute(s, x='m', y='z', e1='%@aol.com', e2='%@msn.com').fetchall() 
[(u'Wendy Williams, wendy@aol.com',)]

First, take your SQL string and pass it to sqalchemy.sql.text(). This isn't necessary, but probably a good idea...

The advantages text() provides over a plain string are backend-neutral support for bind parameters, per-statement execution options, as well as bind parameter and result-column typing behavior, allowing SQLAlchemy type constructs to play a role when executing a statement that is specified literally.

Note that even if you didn't use text(), you should NEVER just use sql.format(...). This leads to greater risk of SQL injection attacks.

Next, you can specify the actual arguments using keyword parameters to the execute() function you've already been using.

Now, in your example, you have a function that wraps the execute functionality. So, if you want to use this for multiple queries, you'll need to make the parameters able to receive your arguments. You could do this pretty simple as a dictionary:

def _sql_to_data(sql, values):
    ...
    conn.execute(sql, values)

values would be a dictionary.You could then use your function like this...

sql = 'SELECT ...'
data = { 'user_id' : 3 }
results = _sql_to_data(sql, data)

Using keywords as your parameters is just one way of specifying the arguments to the execute() function. You can read the documentation for that function for a few different ways.

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      • 2
    • text does not let you create a list of values which is a tremendous downside and often makes it unusable in many of my cases making format the only real way.
      • 2
    • @stevenwade Format is never the real way, unleas you mean formatting the required placeholders for the list values, and SQLAlchemy even does it for you using bindparam(..., expanding=True). On the other hand some DB-API drivers adapt arrays out of the box to suitable SQL.
      • 1
    • Thank you, my bad, by some reason I was not able to find this in doc. My only one excuse SQLAlchemy doc is somewhat fragmented with emphasis on ORM.
      • 1
    • One more question - how fetchAll() and then itterating in results data structure relates to for row in rows in terms of memory consumption?

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