Django QuerySets, how to express EXISTS ... IN ...
Hello,
I am trying to find how to filter the entries of my blog by a set of
tags, using the Django models.
In particular there are two relations:
Blog (id, title, content)
Tag ( name, blog_id )
with Tag.blog_id foreign key of Blog.id
I want to select all blog entries that contain a certain set of tags.
For instance, I would express the query in SQL as:
SELECT * FROM blog_blog b WHERE EXISTS ( SELECT 1 FROM blog_tag t WHERE
t.blog_id = b.id AND lower(t.name) IN ('tag1', 'tag2', 'tag3') );
How to represent the same query with the Django QuerySets ?
Thanks,
Dean De Leo
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Re: Django QuerySets, how to express EXISTS ... IN ...
mytag = Tag.objects.get(id=1)
mytag.blog_set.all()
Em domingo, 8 de fevereiro de 2015 14:30:25 UTC-2, Dean De Leo escreveu:
>
> Hello,
> I am trying to find how to filter the entries of my blog by a set of
> tags, using the Django models.
> In particular there are two relations:
> Blog (id, title, content)
> Tag ( name, blog_id )
> with Tag.blog_id foreign key of Blog.id
> I want to select all blog entries that contain a certain set of tags.
> For instance, I would express the query in SQL as:
> SELECT * FROM blog_blog b WHERE EXISTS ( SELECT 1 FROM blog_tag t WHERE
> t.blog_id = b.id AND lower(t.name) IN ('tag1', 'tag2', 'tag3') );
>
> How to represent the same query with the Django QuerySets ?
>
> Thanks,
> Dean De Leo
>
>
>
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Re: Django QuerySets, how to express EXISTS ... IN ...
Hi, thanks for the reply.
I still get the error:
Exception Type: AttributeError
Exception Value:
'Tag' object has no attribute 'blog_set'
if rawtags:
taglist = rawtags.split('/');
t = Tag.objects.get(name = "Alpha");
blogentries = t.blog_set.all()
else:
blogentries = Blog.objects.all();
My Models:
# My blog
class Blog(models.Model):
title = models.CharField(max_length=255)
content = models.TextField(max_length=1);
dateAdd = models.DateTimeField(auto_now_add=True, null=False);
dateEdit = models.DateTimeField(auto_now=True);
class Meta:
ordering = ['-id']
class Tag(models.Model):
name = models.CharField(max_length=255, null=False)
blog = models.ForeignKey('Blog', null=False)
class Meta:
unique_together = [("name", "blog",)]
ordering = ["name"]
Am I mispelling something?
Thanks,
Dean De Leo
On 08/02/15 16:55, Neto wrote:
> mytag = Tag.objects.get(id=1)
> mytag.blog_set.all()
>
> Em domingo, 8 de fevereiro de 2015 14:30:25 UTC-2, Dean De Leo escreveu:
>
> Hello,
> I am trying to find how to filter the entries of my blog by a set of
> tags, using the Django models.
> In particular there are two relations:
> Blog (id, title, content)
> Tag ( name, blog_id )
> with Tag.blog_id foreign key of Blog.id
> I want to select all blog entries that contain a certain set of tags.
> For instance, I would express the query in SQL as:
> SELECT * FROM blog_blog b WHERE EXISTS ( SELECT 1 FROM blog_tag t
> WHERE
> t.blog_id = b.id AND lower(t.name )
> IN ('tag1', 'tag2', 'tag3') );
>
> How to represent the same query with the Django QuerySets ?
>
> Thanks,
> Dean De Leo
>
>
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Re: Django QuerySets, how to express EXISTS ... IN ...
Your model is incorrect. Each blog has only one tag? So you have only one
result per tag.
Tag.objects.get(name = "Alpha").blog
Em domingo, 8 de fevereiro de 2015 15:43:33 UTC-2, Dean De Leo escreveu:
>
> Hi, thanks for the reply.
> I still get the error:
> Exception Type: AttributeError Exception Value:
>
> 'Tag' object has no attribute 'blog_set'
>
>
> if rawtags:
> taglist = rawtags.split('/');t = Tag.objects.get(name = "Alpha");
> blogentries = t.blog_set.all()else:
> blogentries = Blog.objects.all();
>
>
>
> My Models:
>
> # My blogclass Blog(models.Model):
> title = models.CharField(max_length=255)
> content = models.TextField(max_length=1);
> dateAdd = models.DateTimeField(auto_now_add=True, null=False);
> dateEdit = models.DateTimeField(auto_now=True);
>
> class Meta:
> ordering = ['-id']
>
> class Tag(models.Model):
> name = models.CharField(max_length=255, null=False)
> blog = models.ForeignKey('Blog', null=False)
>
> class Meta:
> unique_together = [("name", "blog",)]
> ordering = ["name"]
>
>
> Am I mispelling something?
>
> Thanks,
> Dean De Leo
>
>
>
> On 08/02/15 16:55, Neto wrote:
>
> mytag = Tag.objects.get(id=1)
> mytag.blog_set.all()
>
> Em domingo, 8 de fevereiro de 2015 14:30:25 UTC-2, Dean De Leo escreveu:
>>
>> Hello,
>> I am trying to find how to filter the entries of my blog by a set of
>> tags, using the Django models.
>> In particular there are two relations:
>> Blog (id, title, content)
>> Tag ( name, blog_id )
>> with Tag.blog_id foreign key of Blog.id
>> I want to select all blog entries that contain a certain set of tags.
>> For instance, I would express the query in SQL as:
>> SELECT * FROM blog_blog b WHERE EXISTS ( SELECT 1 FROM blog_tag t WHERE
>> t.blog_id = b.id AND lower(t.name) IN ('tag1', 'tag2', 'tag3') );
>>
>> How to represent the same query with the Django QuerySets ?
>>
>> Thanks,
>> Dean De Leo
>>
>>
>>
>
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