Tag "db"

SQLite database vacuum script

This script can be run periodically (e.g. as a nightly cronjob) to keep a SQLite database with high churn from growing unnecessarily large.

• db
• utility
• sqlite

Sun 11 Jul 2010 Read More

Allow filtering and ordering by counts of related query results

I know you're thinking, *what the heck could that title mean?* I often find myself wanting to filter and order by the result of a COUNT(*) of a query using a method similar to the [entry_count example](http://www.djangoproject.com/documentation/db-api/#extra-select-none-where-none-params-none-tables-none). Writing this many times is tedious and hardcoding the table and column names made me cringe, I also wanted the counts to result from more complex queries. This is a method you can add to your custom Manager to do this easily. It's not an ideal syntax, but it's good for the amount of code required. Example: suppose we have some articles we want to filter and order by comments and visit logs to show the most popular... class ArticleManager(models.Manager): count_related = _count_related class Article(models.Model): pub_date = models.DateTimeField(auto_now_add=True) objects = ArticleManager() class Comment(models.Model): article = models.ForeignKey(Article) is_spam = models.BooleanField(default=False) class Visit(models.Model): article = models.ForeignKey(Article) referrer = models.URLField(verify_exists=False) search_query = models.CharField(maxlength=200) Notice how the ArticleManager is given the `count_related` method. Now you can find the most popular like so... Order by non-spam comments: Article.objects.count_related(Comment.objects.filter( is_spam=False)).order_by('-comment__count') Order by incoming non-search-engine links: Article.objects.count_related(Visit.objects.filter( referrer__isnull=False, search_query__isnull=True), 'links').order_by('-links') Order by total visits: Article.objects.count_related(Visit).order_by('-visit__count') Note: Doesn't work if `query` contains joins or for many-to-many relationships, but those could be made to work identically if there's demand.

• sql
• model
• db
• count
• manager

Tue 14 Feb 2012 Read More

Template tag to dump database query info

This snippet introduces two tags: `{%dbinfo%}` and `{%dbquerylist%}`. The `{%dbinfo%}` tag returns a string with the # of database queries and aggregate DB time. The `{%dbquerylist%}` tag expands to a set of <LI> elements containing the actual SQL queries executed. If `settings.TEMPLATE_DEBUG` is False, both tags return empty strings.

• tag
• db
• debugging

Mon 06 Feb 2012 Read More

Filter on Multiple M2M Objects Simultaneously

This snippet should allow you to do queries not before possible using Django's ORM. It allows you to "Split" up the m2m object you are filtering on. This is best described by example: Suppose you have `Article` and `Tag`, where `Article` has a m2m relation with `Tag` (`related_name = 'tag'`). If I run: from django.db.models.query import Q Article.objects.filter(Q(tag__value = 'A') & Q(tag__value = 'B')) > # no results I would expect to get no results (there are no tags with both a value of 'A' and 'B'). However, I *would* like to somehow get a list of articles with tags meeting that criteria. Using this snippet, you can: from django.db.models.query import Q from path.to.qsplit import QSplit Article.objects.filter(QSplit(Q(tag__value = 'A')) & QSplit(Q(tag__value = 'B'))) > # articles with both tags So now they are split into different `Tag` entries. Notice how the `QSplit()` constructor takes a `Q` object---it's possible to give this any complicated Q-type expression.

• models
• q
• m2m
• db
• orm

Sun 11 Jul 2010 Read More