Re: How to formulate a query over two models?

[Simon Charette]

Hello there,

If you are using PostgreSQL you can achieve it using ArrayAgg[0]

queryset = 
MetaData.objects.annotate(values=ArrayAgg('metadatavalue__value'))
map = dict(queryset.values_list('name', 'values'))

Cheers,
Simon

[0] https://docs.djangoproject.com/en/2.0/ref/contrib/postgres/aggregates/

Le mercredi 11 avril 2018 19:06:06 UTC-4, mark a écrit :
>
> I have two models:
>
> # MetaData
> class MetaData(models.Model):
> metadata_id = models.AutoField(primary_key = True)
> name = models.CharField('metadata name', max_length=200, unique=True)
> description = models.TextField('description')
>
> def __str__(self):
> return self.name
>
> # MetaData Value
> class MetaDataValue(models.Model):
> metadata_id = models.ForeignKey(MetaData, on_delete=models.CASCADE,)
> value = models.CharField('value', max_length=200, unique=True)
>
> def __str__(self):
> return self.value
>
> I want to construct a query set such that I get a dictionary back that 
> looks like this:
>
> {name1: [value1, value2,..], name2:[value3, value4,..]..}
>
> In other words, a dictionary that has the metadata name as the key and the 
> associated values for that name in a list.
>
> I have been playing around with MetaData.objects.all(), but I don't see 
> how to relate the two models and get something close to what I want.
>
> Thanks!
>
> Mark
>
>
>

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Re: How to formulate a query over two models?

[Christophe Pettus]

> On Apr 11, 2018, at 16:19, Mark Phillips  wrote:
> 
> Thanks for the link - I have read it before. I need to stay with these 
> models, so is there a simple query to get my result, or do I have to make 
> multiple queries and combine the data in python?

If you are using PostgreSQL, you can do it as a raw SQL query; otherwise, 
you'll need to transform the data in Python.

--
-- Christophe Pettus
   x...@thebuild.com

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Re: How to formulate a query over two models?

[Mark Phillips]

Thanks for the link - I have read it before. I need to stay with these
models, so is there a simple query to get my result, or do I have to make
multiple queries and combine the data in python?

Thanks,

Mark

On Wed, Apr 11, 2018 at 4:14 PM, Christophe Pettus  wrote:

>
> > On Apr 11, 2018, at 16:05, Mark Phillips 
> wrote:
> >
> > I have two models:
> >
> > # MetaData
> > # MetaData Value
>
> First, you might want to make sure this is *really* the best way of
> representing your data:
>
> http://karwin.blogspot.com/2009/05/eav-fail.html
>
> That being said, you might consider getting rid of the MetaDataValue
> table, and putting the values in as a JSON field on MetaData.
>
> --
> -- Christophe Pettus
>x...@thebuild.com
>
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> msgid/django-users/8B07A737-9B74-4389-8423-A6CD3C7BCA58%40thebuild.com.
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>

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Re: How to formulate a query over two models?

[Christophe Pettus]

> On Apr 11, 2018, at 16:05, Mark Phillips  wrote:
> 
> I have two models:
> 
> # MetaData
> # MetaData Value

First, you might want to make sure this is *really* the best way of 
representing your data:

http://karwin.blogspot.com/2009/05/eav-fail.html

That being said, you might consider getting rid of the MetaDataValue table, and 
putting the values in as a JSON field on MetaData.

--
-- Christophe Pettus
   x...@thebuild.com

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