Re: Do people actually squash migrations?

[Shai Berger]

On Wed, 12 May 2021 09:37:53 -0700 (PDT)
"'Mike Lissner' via Django developers  (Contributions to Django
itself)"  wrote:

> 
> I haven't done the manual approach but I imagine it's something like:
> 
> 1. Check your migrations across all apps with interdependencies for 
> RunPython or RunSQL code.
> 2. If found, make a decision about keeping or deleting that code.
> 3. Delete all migrations across all apps that have interdependencies.
> 4. Run the makemigrations command
> 5. Add your custom RunPython or RunSQL code back
> 

I've tried it. In my experience, it isn't as easy as described either.

When you have circular dependencies between the migration of apps, in
many (most?) cases it means you also have circular dependencies between
the models (FKs etc going in both directions). When that happens,
makemigrations from scratch doesn't do the right thing either --
basically, you need to recreate the interdependencies by having each
app's models created in two steps: One for the "core" of  the models,
so they all exist, and one for the relations, which can only be added
once all the referenced models are present.

The makemigrations command will only add one migration per app, and so
it cannot do this. I haven't tried this in a while, so I don't remember
if the command actually fails, or just produces non-working migrations
which you then need to edit by hand.

This all ties in to a discussion we had on the forum, about the
separation to apps in large projects (linking to my own post there, but
the whole discussion is worth a read if you haven't):
https://forum.djangoproject.com/t/why-do-we-need-apps/827/20

Have fun,
Shai.

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Re: Do people actually squash migrations?

[Hanne Moa]

On Wed, 12 May 2021 at 18:40, 'Mike Lissner' via Django developers
(Contributions to Django itself) 
wrote:
> Oh, I guess there's also a step in the manual process to reset the migrations 
> table in the DB, but I don't know how to do that. Tricky stuff!

I've made a management command for that: resetmigrationhistory, which
nukes just the migrations of *my* apps. Then I run migrate --fake
manually afterwards.

I squash as part of any major release (semver). Rewrite them a lot by
hand to get rid of any datamigrations and have lots of extra
mini-releseas to make sure everything works etc.

There's https://github.com/kingbuzzman/django-squash, which I have
considered using, their "elidable" concept is very good.


HM

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Re: Do people actually squash migrations?

['Mike Lissner' via Django developers (Contributions to Django itself)]

Thanks for those links. I went ahead and filed a PR that describes a new
"Migration Trimming" process. I'd love comments and suggestions if folks
are interested and able:

https://github.com/django/django/pull/14408

Mike

On Mon, May 17, 2021 at 8:27 AM René Fleschenberg 
wrote:

> Hi,
>
> I agree that it would be good to extend the docs and to describe how to
> reset a project's migrations. Some prior art on this:
>
> https://geekchick77.dreamwidth.org/5560.html
>
>
> https://simpleisbetterthancomplex.com/tutorial/2016/07/26/how-to-reset-migrations.html
>
>
> Regards,
> René
>
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>


-- 
Mike Lissner
Executive Director
Free Law Project
https://free.law

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Re: Do people actually squash migrations?

[René Fleschenberg]

Hi,

I agree that it would be good to extend the docs and to describe how to
reset a project's migrations. Some prior art on this:

https://geekchick77.dreamwidth.org/5560.html

https://simpleisbetterthancomplex.com/tutorial/2016/07/26/how-to-reset-migrations.html


Regards,
René

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Re: Do people actually squash migrations?

[Raffaele Salmaso]

On Wed, May 12, 2021 at 2:50 AM 'Mike Lissner' via Django developers
(Contributions to Django itself)  wrote:

> So, my question is: Do people actually use squashmigrations with success?

For what is worth: yes. The only problem I have is a pbcak problem (I like
to do esoteric things just because).

-- 
| Raffaele Salmaso
| https://salmaso.org
| https://bitbucket.org/rsalmaso
| https://github.com/rsalmaso

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Re: Do people actually squash migrations?

[Ryan Hiebert]

You’d run the migrations that you manually created with --fake. My experience 
also corroborates the idea that squashmigrations may be unsuitable for many 
situation that are similar to mine, where I am able to fully control the full 
set of places that the code is deployed.

Ryan

> On May 12, 2021, at 11:40 AM, 'Mike Lissner' via Django developers 
> (Contributions to Django itself)  wrote:
> 
> Oh, I guess there's also a step in the manual process to reset the migrations 
> table in the DB, but I don't know how to do that. Tricky stuff! 
> 
> On Wednesday, May 12, 2021 at 9:37:53 AM UTC-7 Mike Lissner wrote:
> So sort of sounds like an update to the squash migration docs is needed if 
> this is representative of the general sentiment. Looking at the section on 
> this 
> ,
>  the general outline is:
> 
> 1. Overview
> 2. How it works
> 3. The commands
> 4. Gotchas
> 5. A bunch of wonky stuff you have to do ("Update all migrations that depend 
> on the deleted migrations", "Remove the 'replaces' attribute in the Migration 
> class ")
> 6. Another gotcha in an info box
> 
> Would it be a bad idea to update the docs to bifurcate this section so it has 
> an intro that says something like:
> 
> As you work on your project you will create more and more migrations. When 
> they get to be too many, there are two approaches to trimming them down. The 
> first is to use the squashmigrations command and process to create a merged 
> migration file, however this approach comes with a number of caveats and 
> gotchas that often make it impractical. The second way is to coordinate with 
> your team to ensure that all installations of your app are up to date, then 
> to have a coordinated day when migrations are removed and recreated from 
> scratch. Which one is best for your organization will depend on the 
> complexity of your project and the flexibility of your team.
> 
> From there, the docs could go on to explain first how to do this manually, 
> then move onto the squashmigrations docs. This disfavors squashmigrations by 
> putting it after the manual approach, but after this conversation (and my 
> experience) that seems right to me. 
> 
> I haven't done the manual approach but I imagine it's something like:
> 
> 1. Check your migrations across all apps with interdependencies for RunPython 
> or RunSQL code.
> 2. If found, make a decision about keeping or deleting that code.
> 3. Delete all migrations across all apps that have interdependencies.
> 4. Run the makemigrations command
> 5. Add your custom RunPython or RunSQL code back
> 
> That'd be a big demotion for the squashmigrations code. I don't know how 
> married we are to it, but it seems like there's not much energy for making it 
> better and that lots of people have already demoted it in their minds and 
> workflows.
> 
> Thanks, 
> 
> 
> Mike
> 
> 
>  
> 
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>  
> .

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Re: Do people actually squash migrations?

['Mike Lissner' via Django developers (Contributions to Django itself)]

Oh, I guess there's also a step in the manual process to reset the 
migrations table in the DB, but I don't know how to do that. Tricky stuff! 

On Wednesday, May 12, 2021 at 9:37:53 AM UTC-7 Mike Lissner wrote:

> So sort of sounds like an update to the squash migration docs is needed if 
> this is representative of the general sentiment. Looking at the section 
> on this 
> ,
>  
> the general outline is:
>
> 1. Overview
> 2. How it works
> 3. The commands
> 4. Gotchas
> 5. A bunch of wonky stuff you have to do ("Update all migrations that 
> depend on the deleted migrations", "Remove the 'replaces' attribute in 
> the Migration class ")
> 6. Another gotcha in an info box
>
> Would it be a bad idea to update the docs to bifurcate this section so it 
> has an intro that says something like:
>
> As you work on your project you will create more and more migrations. When 
>> they get to be too many, there are two approaches to trimming them down. 
>> The first is to use the squashmigrations command and process to create a 
>> merged migration file, however this approach comes with a number of caveats 
>> and gotchas that often make it impractical. The second way is to coordinate 
>> with your team to ensure that all installations of your app are up to date, 
>> then to have a coordinated day when migrations are removed and recreated 
>> from scratch. Which one is best for your organization will depend on the 
>> complexity of your project and the flexibility of your team.
>>
>
> From there, the docs could go on to explain first how to do this manually, 
> then move onto the squashmigrations docs. This disfavors squashmigrations 
> by putting it after the manual approach, but after this conversation (and 
> my experience) that seems right to me. 
>
> I haven't done the manual approach but I imagine it's something like:
>
> 1. Check your migrations across all apps with interdependencies for 
> RunPython or RunSQL code.
> 2. If found, make a decision about keeping or deleting that code.
> 3. Delete all migrations across all apps that have interdependencies.
> 4. Run the makemigrations command
> 5. Add your custom RunPython or RunSQL code back
>
> That'd be a big demotion for the squashmigrations code. I don't know how 
> married we are to it, but it seems like there's not much energy for making 
> it better and that lots of people have already demoted it in their minds 
> and workflows.
>
> Thanks, 
>
>
> Mike
>
>
>  
>

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Re: Do people actually squash migrations?

['Mike Lissner' via Django developers (Contributions to Django itself)]

So sort of sounds like an update to the squash migration docs is needed if 
this is representative of the general sentiment. Looking at the section on 
this 
,
 
the general outline is:

1. Overview
2. How it works
3. The commands
4. Gotchas
5. A bunch of wonky stuff you have to do ("Update all migrations that 
depend on the deleted migrations", "Remove the 'replaces' attribute in the 
Migration class ")
6. Another gotcha in an info box

Would it be a bad idea to update the docs to bifurcate this section so it 
has an intro that says something like:

As you work on your project you will create more and more migrations. When 
> they get to be too many, there are two approaches to trimming them down. 
> The first is to use the squashmigrations command and process to create a 
> merged migration file, however this approach comes with a number of caveats 
> and gotchas that often make it impractical. The second way is to coordinate 
> with your team to ensure that all installations of your app are up to date, 
> then to have a coordinated day when migrations are removed and recreated 
> from scratch. Which one is best for your organization will depend on the 
> complexity of your project and the flexibility of your team.
>

>From there, the docs could go on to explain first how to do this manually, 
then move onto the squashmigrations docs. This disfavors squashmigrations 
by putting it after the manual approach, but after this conversation (and 
my experience) that seems right to me. 

I haven't done the manual approach but I imagine it's something like:

1. Check your migrations across all apps with interdependencies for 
RunPython or RunSQL code.
2. If found, make a decision about keeping or deleting that code.
3. Delete all migrations across all apps that have interdependencies.
4. Run the makemigrations command
5. Add your custom RunPython or RunSQL code back

That'd be a big demotion for the squashmigrations code. I don't know how 
married we are to it, but it seems like there's not much energy for making 
it better and that lots of people have already demoted it in their minds 
and workflows.

Thanks, 


Mike


 

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Re: Do people actually squash migrations?

[Andrew Godwin]

Migration squashing was always meant to be something that was useful in a rapid 
development environment where you can't control all the installs (since it was 
a feature developed alongside a CMS run by many clients at the time).

If you have control of all the places your project is installed and can have 
everyone developing on it do something at once, you can just do it via a 
complete migration reset and be happy. Squashing is for a very specific 
backwards-compatibility scenario that, I suspect, many Django projects 
developed internally are not in.

Andrew

On Tue, May 11, 2021, at 7:58 PM, Kye Russell wrote:
> I’ve never successfully squashed my migrations to any material degree, but 
> I’ve chalked that up to lack of doing it with any regularity. I suspect that 
> squashing works a lot better if you aren’t trying to clean up a mess of 
> hundreds of migrations files over 5 years, which is where I find myself! 
> 
> Kye
> On 12 May 2021, 9:31 AM +0800, Matthew Pava , wrote:
> 
>> I've had similar issues. I just avoid squashing anymore. It's just not with 
>> the pain, and having so many little files that get looked at a minimal 
>> amount of time isn't worth fretting over. Saying that, I'd love to get it 
>> fixed...
>> 
>> 
>> Sent from my Verizon, Samsung Galaxy smartphone
>> 
>> Get Outlook for Android <https://aka.ms/ghei36>
>> 
>> 
>> *From:* 'Mike Lissner' via Django developers (Contributions to Django 
>> itself) 
>> *Sent:* Tuesday, May 11, 2021 7:50:31 PM
>> *To:* Django developers (Contributions to Django itself) 
>> 
>> *Subject:* Do people actually squash migrations? 
>>  
>> I have a pretty big django project, and since I created the 100th migration 
>> within one of its apps today, I thought I'd finally do some squashing. It 
>> hasn't gone well, but I eventually got the data migrations cleaned up.
>> 
>> Finally, I run it, and it runs smack into a CircularDependencyError, as 
>> described here:
>> 
>> https://code.djangoproject.com/ticket/23337
>> 
>> Basically, from what I understand, after the squash you have one migration 
>> that depends on various others from your other apps. Naturally, that totally 
>> falls over, because can't go from this series of migrations:
>> 
>> app1: migration 1
>> app2: migration 1
>> app2: migration 2
>> app1: migration 2
>> 
>> To, well...any series of migrations in which migration 1&2 from app1 or app2 
>> have been squashed. The docs have something to say about this*, but it feels 
>> like this must affect practically any biggish project.
>> 
>> Stackoverflow also has a variety of dubious (and very complex) advice (read 
>> it and weep):
>> 
>> https://stackoverflow.com/questions/37711402/circular-dependency-when-squashing-django-migrations
>> 
>> So, my question is: Do people actually use squashmigrations with success? 
>> And if not, is it reasonable to consider deprecating it or fixing the bug, 
>> or updating the docs to loudly say it largely doesn't work? I'm surprised 
>> the issue above has so little movement since it was created seven years ago.
>> 
>> Maybe it's just me? If not, it'd be nice to do something to help future 
>> people with ambitions of a simple squash.
>> 
>> Thanks,
>> 
>> 
>> Mike
>>  
>> * Note that model interdependencies in Django can get very complex, and 
>> squashing may result in migrations that do not run; either mis-optimized (in 
>> which case you can try again with --no-optimize, though you should also 
>> report an issue), or with a CircularDependencyError, in which case you can 
>> manually resolve it.
>> To manually resolve a CircularDependencyError, break out one of the 
>> ForeignKeys in the circular dependency loop into a separate migration, and 
>> move the dependency on the other app with it. If you’re unsure, see how 
>> makemigrations 
>> <https://us-east-2.protection.sophos.com/?d=djangoproject.com=aHR0cHM6Ly9kb2NzLmRqYW5nb3Byb2plY3QuY29tL2VuLzMuMS9yZWYvZGphbmdvLWFkbWluLyNkamFuZ28tYWRtaW4tbWFrZW1pZ3JhdGlvbnM==NWVjN2YxNzUxNGEyNzMxNmMyMGRkZGU1=OVFwYmVaMGVKZ2phcWpWUmRBZmZFK09TQjh6bGtHaGpCVXdGSklWVWZ0ND0==b5f442795e5e456485245d491bee80a4>
>>  deals with the problem when asked to create brand new migrations from your 
>> models. In a future release of Django, squashmigrations 
>> <https://us-east-2.protection.sophos.com/?d=djangoproject.com=aHR0cHM6Ly9kb2NzLmRqYW5nb3Byb2plY3QuY29tL2VuLzMuMS9yZWYvZGphbmdvLWFkbWluLyNkamFuZ28tYWRtaW4tc3F1YXNobWlncmF0aW9ucw===NWVjN2YxNzUxNGEyNzMxNmMyMGRkZGU1=SWNaWFlpZWFoSWZNNXQ0c240V2ovN0JOKysvNDJlWHM5cnRVQ3BHNml

Re: Do people actually squash migrations?

[Benny]

Sorry in advance of this isn’t helpful - We’ve done it successfully a few times 
since 1.11… but not without a sacrifice of the virgins-in-volcano variety. Just 
about any kind of RunPython command seems to get in the way. And sometimes it’s 
easier to blow them all away and create fresh migrations.

I have faith in migration squashing. It feels like more art than science, and 
to be sure - dealing with a database is more art than science in general… 
especially with all the creative minds that have access to such a logical 
system. I believe squashing should be used with care, and mostly on systems 
with ideal schema. Aside of that, I’ve worked on projects with migrations in 
the several-hundreds which took long enough to stand up that I could get a 
coffee and continue working.

All that said, I think it’s a nice-to-have feature, but ultimately isn’t 
necessary for the vast majority of projects. 

Benny

> On May 11, 2021, at 7:50 PM, 'Mike Lissner' via Django developers 
> (Contributions to Django itself)  wrote:
> 
> I have a pretty big django project, and since I created the 100th migration 
> within one of its apps today, I thought I'd finally do some squashing. It 
> hasn't gone well, but I eventually got the data migrations cleaned up. 
> 
> Finally, I run it, and it runs smack into a CircularDependencyError, as 
> described here:
> 
> https://code.djangoproject.com/ticket/23337
> 
> Basically, from what I understand, after the squash you have one migration 
> that depends on various others from your other apps. Naturally, that totally 
> falls over, because can't go from this series of migrations:
> 
> app1: migration 1
> app2: migration 1
> app2: migration 2
> app1: migration 2
> 
> To, well...any series of migrations in which migration 1&2 from app1 or app2 
> have been squashed. The docs have something to say about this*, but it feels 
> like this must affect practically any biggish project. 
> 
> Stackoverflow also has a variety of dubious (and very complex) advice (read 
> it and weep):
> 
> https://stackoverflow.com/questions/37711402/circular-dependency-when-squashing-django-migrations
> 
> So, my question is: Do people actually use squashmigrations with success? And 
> if not, is it reasonable to consider deprecating it or fixing the bug, or 
> updating the docs to loudly say it largely doesn't work? I'm surprised the 
> issue above has so little movement since it was created seven years ago. 
> 
> Maybe it's just me? If not, it'd be nice to do something to help future 
> people with ambitions of a simple squash.
> 
> Thanks,
> 
> 
> Mike
>  
> * Note that model interdependencies in Django can get very complex, and 
> squashing may result in migrations that do not run; either mis-optimized (in 
> which case you can try again with --no-optimize, though you should also 
> report an issue), or with a CircularDependencyError, in which case you can 
> manually resolve it.
> To manually resolve a CircularDependencyError, break out one of the 
> ForeignKeys in the circular dependency loop into a separate migration, and 
> move the dependency on the other app with it. If you’re unsure, see how 
> makemigrations deals with the problem when asked to create brand new 
> migrations from your models. In a future release of Django, squashmigrations 
> will be updated to attempt to resolve these errors itself. [Author's note: 
> These sentences really leave me blowing in the wind...maybe I can figure out 
> what they mean, I guess? I thought squashing was supposed to be easy.]
> 
> 
> 
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Re: Do people actually squash migrations?

[Kye Russell]

I’ve never successfully squashed my migrations to any material degree, but I’ve 
chalked that up to lack of doing it with any regularity. I suspect that 
squashing works a lot better if you aren’t trying to clean up a mess of 
hundreds of migrations files over 5 years, which is where I find myself!

Kye
On 12 May 2021, 9:31 AM +0800, Matthew Pava , wrote:
> I've had similar issues. I just avoid squashing anymore. It's just not with 
> the pain, and having so many little files that get looked at a minimal amount 
> of time isn't worth fretting over. Saying that, I'd love to get it fixed...
>
> Sent from my Verizon, Samsung Galaxy smartphone
> Get Outlook for Android
>
> From: 'Mike Lissner' via Django developers (Contributions to Django itself) 
> 
> Sent: Tuesday, May 11, 2021 7:50:31 PM
> To: Django developers (Contributions to Django itself) 
> 
> Subject: Do people actually squash migrations?
>
> I have a pretty big django project, and since I created the 100th migration 
> within one of its apps today, I thought I'd finally do some squashing. It 
> hasn't gone well, but I eventually got the data migrations cleaned up.
>
> Finally, I run it, and it runs smack into a CircularDependencyError, as 
> described here:
>
> https://code.djangoproject.com/ticket/23337
>
> Basically, from what I understand, after the squash you have one migration 
> that depends on various others from your other apps. Naturally, that totally 
> falls over, because can't go from this series of migrations:
>
> app1: migration 1
> app2: migration 1
> app2: migration 2
> app1: migration 2
>
> To, well...any series of migrations in which migration 1&2 from app1 or app2 
> have been squashed. The docs have something to say about this*, but it feels 
> like this must affect practically any biggish project.
>
> Stackoverflow also has a variety of dubious (and very complex) advice (read 
> it and weep):
>
> https://stackoverflow.com/questions/37711402/circular-dependency-when-squashing-django-migrations
>
> So, my question is: Do people actually use squashmigrations with success? And 
> if not, is it reasonable to consider deprecating it or fixing the bug, or 
> updating the docs to loudly say it largely doesn't work? I'm surprised the 
> issue above has so little movement since it was created seven years ago.
>
> Maybe it's just me? If not, it'd be nice to do something to help future 
> people with ambitions of a simple squash.
>
> Thanks,
>
>
> Mike
>
> * Note that model interdependencies in Django can get very complex, and 
> squashing may result in migrations that do not run; either mis-optimized (in 
> which case you can try again with --no-optimize, though you should also 
> report an issue), or with a CircularDependencyError, in which case you can 
> manually resolve it.
> To manually resolve a CircularDependencyError, break out one of the 
> ForeignKeys in the circular dependency loop into a separate migration, and 
> move the dependency on the other app with it. If you’re unsure, see how 
> makemigrations deals with the problem when asked to create brand new 
> migrations from your models. In a future release of Django, squashmigrations 
> will be updated to attempt to resolve these errors itself. [Author's note: 
> These sentences really leave me blowing in the wind...maybe I can figure out 
> what they mean, I guess? I thought squashing was supposed to be easy.]
>
>
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Re: Do people actually squash migrations?

[Matthew Pava]

I've had similar issues. I just avoid squashing anymore. It's just not with the 
pain, and having so many little files that get looked at a minimal amount of 
time isn't worth fretting over. Saying that, I'd love to get it fixed...

Sent from my Verizon, Samsung Galaxy smartphone
Get Outlook for Android<https://aka.ms/ghei36>


From: 'Mike Lissner' via Django developers (Contributions to Django itself) 

Sent: Tuesday, May 11, 2021 7:50:31 PM
To: Django developers (Contributions to Django itself) 

Subject: Do people actually squash migrations?

I have a pretty big django project, and since I created the 100th migration 
within one of its apps today, I thought I'd finally do some squashing. It 
hasn't gone well, but I eventually got the data migrations cleaned up.

Finally, I run it, and it runs smack into a CircularDependencyError, as 
described here:

https://code.djangoproject.com/ticket/23337

Basically, from what I understand, after the squash you have one migration that 
depends on various others from your other apps. Naturally, that totally falls 
over, because can't go from this series of migrations:

app1: migration 1
app2: migration 1
app2: migration 2
app1: migration 2

To, well...any series of migrations in which migration 1&2 from app1 or app2 
have been squashed. The docs have something to say about this*, but it feels 
like this must affect practically any biggish project.

Stackoverflow also has a variety of dubious (and very complex) advice (read it 
and weep):

https://stackoverflow.com/questions/37711402/circular-dependency-when-squashing-django-migrations

So, my question is: Do people actually use squashmigrations with success? And 
if not, is it reasonable to consider deprecating it or fixing the bug, or 
updating the docs to loudly say it largely doesn't work? I'm surprised the 
issue above has so little movement since it was created seven years ago.

Maybe it's just me? If not, it'd be nice to do something to help future people 
with ambitions of a simple squash.

Thanks,


Mike

* Note that model interdependencies in Django can get very complex, and 
squashing may result in migrations that do not run; either mis-optimized (in 
which case you can try again with --no-optimize, though you should also report 
an issue), or with a CircularDependencyError, in which case you can manually 
resolve it.

To manually resolve a CircularDependencyError, break out one of the ForeignKeys 
in the circular dependency loop into a separate migration, and move the 
dependency on the other app with it. If you’re unsure, see how 
makemigrations<https://us-east-2.protection.sophos.com?d=djangoproject.com=aHR0cHM6Ly9kb2NzLmRqYW5nb3Byb2plY3QuY29tL2VuLzMuMS9yZWYvZGphbmdvLWFkbWluLyNkamFuZ28tYWRtaW4tbWFrZW1pZ3JhdGlvbnM==NWVjN2YxNzUxNGEyNzMxNmMyMGRkZGU1=OVFwYmVaMGVKZ2phcWpWUmRBZmZFK09TQjh6bGtHaGpCVXdGSklWVWZ0ND0==b5f442795e5e456485245d491bee80a4>
 deals with the problem when asked to create brand new migrations from your 
models. In a future release of Django, 
squashmigrations<https://us-east-2.protection.sophos.com?d=djangoproject.com=aHR0cHM6Ly9kb2NzLmRqYW5nb3Byb2plY3QuY29tL2VuLzMuMS9yZWYvZGphbmdvLWFkbWluLyNkamFuZ28tYWRtaW4tc3F1YXNobWlncmF0aW9ucw===NWVjN2YxNzUxNGEyNzMxNmMyMGRkZGU1=SWNaWFlpZWFoSWZNNXQ0c240V2ovN0JOKysvNDJlWHM5cnRVQ3BHNmlJUT0==b5f442795e5e456485245d491bee80a4>
 will be updated to attempt to resolve these errors itself. [Author's note: 
These sentences really leave me blowing in the wind...maybe I can figure out 
what they mean, I guess? I thought squashing was supposed to be easy.]



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Do people actually squash migrations?

['Mike Lissner' via Django developers (Contributions to Django itself)]

I have a pretty big django project, and since I created the 100th migration 
within one of its apps today, I thought I'd finally do some squashing. It 
hasn't gone well, but I eventually got the data migrations cleaned up. 

Finally, I run it, and it runs smack into a CircularDependencyError, as 
described here:

https://code.djangoproject.com/ticket/23337

Basically, from what I understand, after the squash you have one migration 
that depends on various others from your other apps. Naturally, that 
totally falls over, because can't go from this series of migrations:

app1: migration 1
app2: migration 1
app2: migration 2
app1: migration 2

To, well...any series of migrations in which migration 1&2 from app1 or 
app2 have been squashed. The docs have something to say about this*, but it 
feels like this must affect practically any biggish project. 

Stackoverflow also has a variety of dubious (and very complex) advice (read 
it and weep):

https://stackoverflow.com/questions/37711402/circular-dependency-when-squashing-django-migrations

So, my question is: Do people actually use squashmigrations with success? 
And if not, is it reasonable to consider deprecating it or fixing the bug, 
or updating the docs to loudly say it largely doesn't work? I'm surprised 
the issue above has so little movement since it was created seven years 
ago. 

Maybe it's just me? If not, it'd be nice to do something to help future 
people with ambitions of a simple squash.

Thanks,


Mike
 
* Note that model interdependencies in Django can get very complex, and 
squashing may result in migrations that do not run; either mis-optimized 
(in which case you can try again with --no-optimize, though you should also 
report an issue), or with a CircularDependencyError, in which case you can 
manually resolve it.

To manually resolve a CircularDependencyError, break out one of the 
ForeignKeys in the circular dependency loop into a separate migration, and 
move the dependency on the other app with it. If you’re unsure, see how 
makemigrations 

 
deals with the problem when asked to create brand new migrations from your 
models. In a future release of Django, squashmigrations 

 
will be updated to attempt to resolve these errors itself. [Author's note: 
These sentences really leave me blowing in the wind...maybe I can figure 
out what they mean, I guess? I thought squashing was supposed to be easy.]


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