On 5/18/06, Malcolm Tredinnick <[EMAIL PROTECTED]> wrote:
[...]
I was helped by Malcom on IRC, so the only decent thing to do, is to
post the solution here.
I'll try to explain as well as I understand it.
First some code:
class Tags(models.Model):
tag = models.CharField(maxlength = 50)
def __str__(self):
return self.tag
class TagManager(models.Manager):
def from_tags(self, tag_list):
id_list = [int(t.id) for t in Tags.objects.filter(tag__in = tag_list)]
all = Contract.objects.extra(tables = ['contracts_tags'], where =
[('contracts_tags.contract_id = contracts.id'), ('(SELECT COUNT(*)
FROM contracts_tags AS t WHERE t.tags_id IN (%s) AND t.contract_id =
contracts.id) = %d' % (','.join([str(tag) for tag in id_list]),
len(id_list)))]).distinct()
return all
class Contract(models.Model):
# Basic things
file = models.FileField()
name = models.CharField(maxlength = 200)
update = models.DateTimeField('date uploaded')
description = models.TextField()
objects = TagManager()
# These are used for indexing
excerpt = models.TextField()
tags = models.ManyToManyField(Tags)
You can call it like this:
tags = ["foo","bar"]
all = Contract.objects.from_tags(tags)
What happens is that you count how many tags match on each contract
ID. Since you only pick out the relevant tags, the count will equal
len(tags), if there's a match. This allows you to search for records
where there's only specific relations, when data is divided across
tables, in this case with a ManyToManyField().
It works fairly well and fast on my somewhat limited set of set, but I
think this would scale fine on a larger scale as well.
Thanks malcom!
--
Jesper Nøhr, Information Systems Developer, Opera Software
tel: +47-24164348 / cell: +47-46056753 / [EMAIL PROTECTED]
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