Allowed memory size exhausted with Propel2 custom query - php

Question

(updates at bottom)
I'm trying to get the latest entry in my table called "VersionHistory", and since the ID is set to auto increment, I was trying to get the max id. Trying to stay away from sorting the whole table in descending order and taking the top as I want to minimize the computation required for this query as the table grows, and this table will probably get pretty huge fast.
class VersionHistoryQuery extends BaseVersionHistoryQuery {
public function getLatestVersion() {
return $this
->withColumn('MAX(version_history.id)')
->limit(1);
}
}
I'm calling the function in my VersionHistory constructor as below:
class VersionHistory extends BaseVersionHistory {
public function __construct($backupPath = "") {
$lastVersion = VersionHistoryQuery::create()
->getLatestVersion()
->find();
$lastVersion->setBackupPath("backup/" . $backupPath);
$lastVersion->save();
parent::setImportedAt(date("Y-m-d H:i:s"));
}
}
This outputs a "Allowed memory size exhausted" error in php. Any idea why? Commenting out the query in the VersionHistory constructor fixes the error, so it's somewhere in the query. I tried setting up a custom query following the instructions here: http://propelorm.org/documentation/03-basic-crud.html#using-custom-sql. But I couldn't get that to work. Running:
SELECT * FROM version_history WHERE id = (SELECT MAX(id) FROM version_history)
From MySQL workbench works fine and quickly.
Any ideas of what I'm doing wrong?
What I tried
Updated the code to:
public function getLatestVersion() {
return $this
->orderById('desc')
->findOne();
}
Still get the same memory allocation error.
Updated the code to:
$lastVersion = VersionHistoryQuery::create()
->orderById('desc')
->findOne();
Removed the custom function, turned on propel debug mode, it outputs that this query is run:
[2015-10-11 17:26:54] shop_reporting_db.INFO: SELECT `version_history`.`id`, `version_history`.`imported_at`, `version_history`.`backup_path` FROM `version_history` ORDER BY `version_history`.`id` DESC LIMIT 1 [] []
Still runs into a memory overflow.

Answer 1

Thats all:
SELECT * FROM version_history ORDER BY id DESC LIMIT 1;

Answer 2

From the documentation, withColumn does the following:
Propel adds the 'with' column to the SELECT clause of the query, and
uses the second argument of the withColumn() call as a column alias.
So, it looks like you are actually querying every row in the table, and also every row is querying the max ID.
I don't know anything about propel (except what I just googled), but it looks like you need a different way to specify your where condition.

Answer 3

Your raw SQL and your Propel Query are different / not equivalent.
In the propel query merely added a column, whereas is your raw SQL your actually have two queries with one being a sub-query to the other.
So you need to do the equivalent in Propel:
$lastVersionID = VersionHistoryQuery::create()
->withColumn('MAX(id)', 'LastVersionID')
->select('LastVersionID')
->findOne();
$lastVersion = VersionHistoryQuery::create()
->filterByVersionHistory($lastVersionID)
->find();
Note the ->select('LatestVersionID') since you only need a scalar value and not an entire object, as well as the virtual column (alias in SQL) using withColumn()