Re: Need help with unique_together - on ForeignKey and Boolean field

[Manjunath]

How are you deciding which post is pinned?
The unique approach might not do any good to you.
A simple solution is to update the pinned values of each post to False & 
setting the required post pinned value to True when you are setting a 
pinned post.
There may be better solutions, but I hope this might help you.


On Friday, October 5, 2018 at 10:06:48 PM UTC+5:30, Chuka Nwadiogbu wrote:
>
> Hi, I know it has been a while since this question was asked but I have  a 
>> similar question. I have a Post model, and I want there to be one pinned 
>> post out of the list of all posts, I tried creating a new property thus, 
>
>
> ```pinned = models.BooleanField(default=False, unique=True)```
>
> but it caused major problems. I want to have just one pinned post and the 
> rest unpinned but that would mean pinned = True for one post/article and 
> pinned=False for the rest and I don't think that is how unique is supposed 
> to work. Unique is supposed to be different for all the objects right? not 
> sure how to tackle this problem.
>
> someone suggested I use a foreignkey field to link them all together but 
> now if I'm being honest, I actually do not know where to go from here 
>
> ```class PinnedPost(models.Model):
> pinned_post = models.ForeignKey(Post, related_name='pinned', 
> on_delete=models.CASCADE)``` 
> if there's anyone here that can help me with this please, I'd really 
> appreciate it. 
>

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Re: Need help with unique_together - on ForeignKey and Boolean field

[heriberto ochoa]

well, maybe using forms, and the parameter initial of the send form to the
template
https://docs.djangoproject.com/en/2.1/ref/forms/fields/#initial
or directly with javascript

El vie., 5 oct. 2018 a las 10:35, Chuka Nwadiogbu ()
escribió:

> Hi, I know it has been a while since this question was asked but I have  a
>> similar question. I have a Post model, and I want there to be one pinned
>> post out of the list of all posts, I tried creating a new property thus,
>
>
> ```pinned = models.BooleanField(default=False, unique=True)```
>
> but it caused major problems. I want to have just one pinned post and the
> rest unpinned but that would mean pinned = True for one post/article and
> pinned=False for the rest and I don't think that is how unique is supposed
> to work. Unique is supposed to be different for all the objects right? not
> sure how to tackle this problem.
>
> someone suggested I use a foreignkey field to link them all together but
> now if I'm being honest, I actually do not know where to go from here
>
> ```class PinnedPost(models.Model):
> pinned_post = models.ForeignKey(Post, related_name='pinned', 
> on_delete=models.CASCADE)```
> if there's anyone here that can help me with this please, I'd really
> appreciate it.
>
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> 
> .
> For more options, visit https://groups.google.com/d/optout.
>

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Re: Need help with unique_together - on ForeignKey and Boolean field

[Chuka Nwadiogbu]

>
> Hi, I know it has been a while since this question was asked but I have  a 
> similar question. I have a Post model, and I want there to be one pinned 
> post out of the list of all posts, I tried creating a new property thus, 

   
```pinned = models.BooleanField(default=False, unique=True)```

but it caused major problems. I want to have just one pinned post and the 
rest unpinned but that would mean pinned = True for one post/article and 
pinned=False for the rest and I don't think that is how unique is supposed 
to work. Unique is supposed to be different for all the objects right? not 
sure how to tackle this problem.

someone suggested I use a foreignkey field to link them all together but 
now if I'm being honest, I actually do not know where to go from here 

```class PinnedPost(models.Model):
pinned_post = models.ForeignKey(Post, related_name='pinned', 
on_delete=models.CASCADE)``` 
if there's anyone here that can help me with this please, I'd really 
appreciate it. 

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Re: Need help with unique_together - on ForeignKey and Boolean field

[ThomasTheDjangoFan]

Hi Javier,

oh yes! You seem to be a really creative and experienced programmer!  [image: 
smile.png] 

My solution will be way number 5:
5) Do not set unique_together - forget about it and give the model a 
function "get_default_image", which returns the first "default_image=True" 
in the list.

Thanks a lot for your help! This was really inpiring! [image: smile.png] 

Have a good one

Am Montag, 17. November 2014 15:12:50 UTC+1 schrieb Javier Guerra:
>
> On Mon, Nov 17, 2014 at 6:10 AM, ThomasTheDjangoFan 
>  wrote: 
> > 
> > How would you do this? Can you give me a hint? 
>
>
> 4 different ways: 
>
> - don't do it as a flag, add a 'defaultImage=ForeignKey(ProductImage)' 
> to the Product class. 
>
> - don't use False for non-default, use NULL.  since two NULL values 
> aren't equal, they don't trip unique restriction 
>
> - don't use True/False, use an integer to give images some priority. 
> #1 is default, the others get 2...n 
>
> - use a partial index (supported by PosgreSQL and SQLite), it's not 
> directly supported by the ORM, but you can simply add as an "ALTER 
> TABLE CREATE UNIQUE INDEX ProductdefaultImage ON app_productimage 
> (image)  WHERE is_default_image;"  at creation and forget about it. 
>
>
> -- 
> Javier 
>

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Re: Need help with unique_together - on ForeignKey and Boolean field

[Javier Guerra Giraldez]

On Mon, Nov 17, 2014 at 6:10 AM, ThomasTheDjangoFan
 wrote:
>
> How would you do this? Can you give me a hint?


4 different ways:

- don't do it as a flag, add a 'defaultImage=ForeignKey(ProductImage)'
to the Product class.

- don't use False for non-default, use NULL.  since two NULL values
aren't equal, they don't trip unique restriction

- don't use True/False, use an integer to give images some priority.
#1 is default, the others get 2...n

- use a partial index (supported by PosgreSQL and SQLite), it's not
directly supported by the ORM, but you can simply add as an "ALTER
TABLE CREATE UNIQUE INDEX ProductdefaultImage ON app_productimage
(image)  WHERE is_default_image;"  at creation and forget about it.


-- 
Javier

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Re: Need help with unique_together - on ForeignKey and Boolean field

[ThomasTheDjangoFan]

Hi Jani,

thanks for making it clear. [image: smile.png]


Actually I would like to assign a lot of images to a product and only have 
one image as the default image.

How would you do this? Can you give me a hint?


Am Montag, 17. November 2014 11:25:37 UTC+1 schrieb Jani Tiainen:
>
> On Sun, 16 Nov 2014 23:51:16 -0800 (PST) 
> ThomasTheDjangoFan  wrote: 
>
> > Hi guys, 
> > 
> > I'd like to only be able to assign many ProcutImages to a Product, but 
> only 
> > ONE Image as a default image per product 
> > (ProductImage.is_default_image=True). 
> > 
> > I can't get this to work correnctly on Django 1.7 with a db.sqlite3: 
> With 
> > the code below I can only assign ONE Image to a Product. After that I 
> get 
> > the error "Product image with this Product und Is default image already 
> > exists.". 
> > 
> > Am I getting something wrong? 
> > 
> > from django.db import models 
> > 
> > class Product(models.Model): 
> > title = models.CharField(max_length=255) 
> > 
> > is_active = models.BooleanField(default=True) 
> > 
> > 
> > class ProductImage(models.Model): 
> > product = models.ForeignKey(Product) 
> > 
> > image = models.ImageField(upload_to='products/images/') 
> > 
> > is_default_image = 
> models.BooleanField(default=False,null=False,blank= 
> > False) 
> > 
> > class Meta: 
> > # A product can have multiple ProductImages, but only one of 
> them 
> > can be the "default"-image 
> > unique_together = ('product', 'is_default_image') 
> > 
> > I would be really thankful for some tips. 
>
> Well boolean field can have only two values: "true" or "false". 
>
> Now your unique_together defines that for "product" combined with 
> "is_default_image" must be unique. Which means that for each product you 
> can have _two_ images, one where is_default_image is true and one where 
> is_default_image is false. And this is forced on database level as well. 
>
> But apparently that is what you intended to do. There isn't really one 
> single solution for your problem. 
>
> -- 
>
> Jani Tiainen 
>

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Re: Need help with unique_together - on ForeignKey and Boolean field

[Jani Tiainen]

On Sun, 16 Nov 2014 23:51:16 -0800 (PST)
ThomasTheDjangoFan  wrote:

> Hi guys,
> 
> I'd like to only be able to assign many ProcutImages to a Product, but only 
> ONE Image as a default image per product 
> (ProductImage.is_default_image=True).
> 
> I can't get this to work correnctly on Django 1.7 with a db.sqlite3: With 
> the code below I can only assign ONE Image to a Product. After that I get 
> the error "Product image with this Product und Is default image already 
> exists.".
> 
> Am I getting something wrong?
> 
> from django.db import models
> 
> class Product(models.Model):
> title = models.CharField(max_length=255)
> 
> is_active = models.BooleanField(default=True)
> 
> 
> class ProductImage(models.Model):
> product = models.ForeignKey(Product)
> 
> image = models.ImageField(upload_to='products/images/')
> 
> is_default_image = models.BooleanField(default=False,null=False,blank=
> False)
> 
> class Meta:
> # A product can have multiple ProductImages, but only one of them 
> can be the "default"-image
> unique_together = ('product', 'is_default_image')
> 
> I would be really thankful for some tips.

Well boolean field can have only two values: "true" or "false".

Now your unique_together defines that for "product" combined with 
"is_default_image" must be unique. Which means that for each product you can 
have _two_ images, one where is_default_image is true and one where 
is_default_image is false. And this is forced on database level as well.

But apparently that is what you intended to do. There isn't really one single 
solution for your problem.

-- 

Jani Tiainen

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Need help with unique_together - on ForeignKey and Boolean field

[ThomasTheDjangoFan]

Hi guys,

I'd like to only be able to assign many ProcutImages to a Product, but only 
ONE Image as a default image per product 
(ProductImage.is_default_image=True).

I can't get this to work correnctly on Django 1.7 with a db.sqlite3: With 
the code below I can only assign ONE Image to a Product. After that I get 
the error "Product image with this Product und Is default image already 
exists.".

Am I getting something wrong?

from django.db import models

class Product(models.Model):
title = models.CharField(max_length=255)

is_active = models.BooleanField(default=True)


class ProductImage(models.Model):
product = models.ForeignKey(Product)

image = models.ImageField(upload_to='products/images/')

is_default_image = models.BooleanField(default=False,null=False,blank=
False)

class Meta:
# A product can have multiple ProductImages, but only one of them 
can be the "default"-image
unique_together = ('product', 'is_default_image')

I would be really thankful for some tips.

Kind regards
Thomas

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