DB schema dumper uncompatibility in Rails 7.0 #43909

mpg-tomohiko-mimura · 2021-12-17T10:00:28Z

Steps to reproduce

git@github.com:mito5525/precision_sample_app.git
cd precision_sample_app
bundle install

bin/rails db:drop db:create db:migrate
bin/rails db:schema:dump
git diff
# There is no difference.

bin/rails db:schema:load
bin/rails db:schema:dump
git diff

Expected behavior

No diffs in schema.rb

Actual behavior

The following differences will occur

diff --git a/db/schema.rb b/db/schema.rb
index 298ff3e..6d02e6b 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -13,7 +13,7 @@
 ActiveRecord::Sch
8000
ema.define(version: 2021_12_17_090228) do

   create_table "tasks", charset: "utf8mb4", force: :cascade do |t|
-    t.datetime "deleted_at"
+    t.datetime "deleted_at", precision: 6
     t.datetime "created_at", precision: 6, null: false
     t.datetime "updated_at", precision: 6, null: false
   end

I think there was a lack of compatibility considerations in #42297.

System configuration

Rails version: v7.0.0

Ruby version: v3.0.3

morgoth · 2022-01-18T14:18:49Z

Same here.

We dump schema from production database backup (so this is our source of truth)
The schema contains columns as timestamp without time zone as this is how it was in previous versions and is in our production db
From this schema.rb we bootstrap local database, which creates columns that are timestamp(6) without time zone so not really what is defined in the schema
On the db:schema:dump the precision: 6 is added

@robertomiranda do you have a clue maybe what could cause it in #42297 ?

bfad · 2022-01-20T16:07:44Z

We are also seeing an issue here. Our schema.rb doesn't specify a precision for MySQL datetimes, and none in set in our databases. However, if we drop and reload our databases in Rails 7, a precision of 6 is added to the MySQL fields, but the schema.rb file remains unchanged.

bfad · 2022-01-20T19:06:43Z

Looks like #44171 may help fix this issue.

morgoth · 2022-01-27T08:00:23Z

The merged PR was about mysql. We're using postgresql, so I think this still will be an issue

rafaelfranca · 2022-01-28T22:10:09Z

Before loading the schema with a new version of Rails you should dump it. I'm going to fix this requirement, but right now that is the correct way to solve the issue.

rafaelfranca · 2022-01-2 8000 8T22:14:13Z

Long term fix is here #44286

Since #42297, Rails now generates datetime columns on MySQL with a default precision of 6. This means that users upgrading to Rails 7.0 from 6.1, when loading the database schema, would get the new precision value, which would not match the production schema. To avoid problems like this in the future, Rails will now freeze `ActiveRecord::Schema` class to be the 7.0 implementation, and will allow access to other version using the same mechanism of `ActiveRecord::Migration`. The schema dumper will generate the new format which will include the Rails version and will look like this: ``` ActiveRecord::Schema[7.0].define ``` Related to #43934 and #43909.

justisb · 2022-02-03T05:34:17Z

Before loading the schema with a new version of Rails you should dump it. I'm going to fix this requirement, but right now that is the correct way to solve the issue.

I don't think that would solve this issue- because the old default precision: nil is not written in the dump. So there is no way to represent the Rails 6.1 (non-timestamps) datetime default precision in schema.rb, as the lack of precision keyword causes db:schema:load to always use precision: 6 in Rails 7.0.

I believe your pending PR that allows specifying the compatibility version of the Schema class will fix it- that solution looks great. But I've found no simple temporary fix, and have currently resorted to monkey patching ActiveRecord::Migration with the Compatibility::V6_1 definitions.

rafaelfranca · 2022-02-07T18:44:54Z

I don't think that would solve this issue- because the old default precision: nil is not written in the dump.

This is already fixed in 7-0-stable.

Since #42297, Rails now generates datetime columns on MySQL with a default precision of 6. This means that users upgrading to Rails 7.0 from 6.1, when loading the database schema, would get the new precision value, which would not match the production schema. To avoid problems like this in the future, Rails will now freeze `ActiveRecord::Schema` class to be the 7.0 implementation, and will allow access to other version using the same mechanism of `ActiveRecord::Migration`. The schema dumper will generate the new format which will include the Rails version and will look like this: ``` ActiveRecord::Schema[7.0].define ``` Related to #43934 and #43909.

justisb · 2022-02-07T19:29:50Z

I don't think that would solve this issue- because the old default precision: nil is not written in the dump.

This is already fixed in 7-0-stable.

I see the patch eca89fd from PR #44171 on 7-0-stable, but that will only affect MySQL and not Postgres, right? Whereas your PR should effectively solve for any DB adapter after setting the schema.rb version to 6.1. Unless you're referring to a different fix.

rafaelfranca · 2022-02-07T19:50:18Z

Postgres should not have that problem. Does it?

justisb · 2022-02-07T20:57:34Z

Here's a minimal reproduction with PG, forked from the MySQL example in the issue description:
https://github.com/justisb/precision_sample_app

bin/rails db:drop db:create db:migrate
bin/rails db:schema:dump
git diff
# No diff

bin/rails db:drop db:create db:schema:load
bin/rails db:schema:dump
git diff
diff --git a/db/schema.rb b/db/schema.rb
index 7664977..5e6ac9c 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -16,7 +16,7 @@ ActiveRecord::Schema.define(version: 2021_12_17_093703) do
   enable_extension "plpgsql"
 
   create_table "tasks", force: :cascade do |t|
-    t.datetime "deleted_at"
+    t.datetime "deleted_at", precision: 6
     t.datetime "created_at", precision: 6, null: false
     t.datetime "updated_at", precision: 6, null: false
   end

rafaelfranca · 2022-02-07T21:24:42Z

Wait, that makes no sense at all. You don't even loaded the schema, so the precision in the database should not be 6. Are those really the steps you took?

morgoth · 2022-02-07T21:27:48Z

@rafaelfranca The steps here #43909 (comment) are reproducing it for PostgreSQL

rafaelfranca · 2022-02-07T21:31:09Z

That is still loading the schema generated in 6.1 without dumping in first in 7.0, so not really reproducing the issue. The fix for that is load the schema in 6.1 and them dump in 7.0.

rafaelfranca · 2022-02-07T21:32:58Z

So steps to fix you problem are:

# Rails 6.1
bin/rails db:schema:load

# Rails 7.0
bin/rails db:schema:dump
# Commit the generated file

Or dump the production database using Rails 7.0.

rafaelfranca · 2022-02-07T22:55:01Z

Ok. I think I got the problem now. #44356 should fix it. Can someone try?

rafaelfranca · 2022-02-07T23:51:37Z

Ok, even #44356 would not fix it. #44358 should.

Since Rails 7.0 the datetime column precision is 6 by default. That means that `t.datetime` calls without setting the `:precision` option would have its precision set to 6. The schema dumper was generating a call without precision for columns with the precision set to `nil` (which has the same effect of 0), making the schema dump incorrect for the next load since that would be interpreted as if the precision was 6. This didn't affect MySQL since #44171, since MySQL precision is 0 by default not `nil` but it affected PostgreSQL and SQLite3. Now the dumper will generate the precision as 0 for columns without precision and omit it when the precision is 6. Related to #43909.

Since rails#42297, Rails now generates datetime columns on MySQL with a default precision of 6. This means that users upgrading to Rails 7.0 from 6.1, when loading the database schema, would get the new precision value, which would not match the production schema. To avoid problems like this in the future, Rails will now freeze `ActiveRecord::Schema` class to be the 7.0 implementation, and will allow access to other version using the same mechanism of `ActiveRecord::Migration`. The schema dumper will generate the new format which will include the Rails version and will look like this: ``` ActiveRecord::Schema[7.0].define ``` Related to rails#43934 and rails#43909.

Since Rails 7.0 the datetime column precision is 6 by default. That means that `t.datetime` calls without setting the `:precision` option would have its precision set to 6. The schema dumper was generating a call without precision for columns with the precision set to `nil` (which has the same effect of 0), making the schema dump incorrect for the next load since that would be interpreted as if the precision was 6. This didn't affect MySQL since rails#44171, since MySQL precision is 0 by default not `nil` but it affected PostgreSQL and SQLite3. Now the dumper will generate the precision as 0 for columns without precision and omit it when the precision is 6. Related to rails#43909.

thisismydesign · 2022-02-28T13:44:29Z

@rafaelfranca I have an issue with postgresql. When we migrated to Rails 7 precision: 6 got added to timestamps in our schema. It worked fine. After updating to 7.0.2 when I run db:migrate this is replaced with precision: nil. After this, one of our spec comparing dates is failing because of what looks like a precision related error:

Diff:
       @@ -1 +1 @@
       -Mon, 21 Feb 2022 14:10:49.640199500 CET +01:00
       +Mon, 21 Feb 2022 14:10:49.640199000 CET +01:00

More importantly, I think this means an actual schema change that would not be reflected on production, only locally.

Opened an issue: #44571

byroot added the activerecord label Dec 17, 2021

tmimura39 mentioned this issue Dec 19, 2021

Invalid datetime(precision nil and zero) Column DB schema dump in Rails 7.0 #43934

Closed

ghiculescu mentioned this issue Dec 20, 2021

Set precision 6 by default for datetime columns #42297

Merged

rafaelfranca closed this as completed Jan 26, 2022

technicalpickles mentioned this issue Jan 28, 2022

Add Rails 7.0 to Appraisals thoughtbot/shoulda-matchers#1485

Closed

rafaelfranca mentioned this issue Jan 28, 2022

Dump the database schema containing the current Rails version #44286

Merged

rafaelfranca mentioned this issue Feb 7, 2022

Dump the precision for datetime columns following the new defaults #44358

Merged

kamipo mentioned this issue Feb 8, 2022

Set the ActiveRecord::Schema version when running the app:update task #44356

Merged

thisismydesign mentioned this issue Feb 28, 2022

precision: nil added to datetime columns in schema.rb in 7.0.2 causes a change in value #44571

Closed

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DB schema dumper uncompatibility in Rails 7.0 #43909

DB schema dumper uncompatibility in Rails 7.0 #43909

DB schema dumper uncompatibility in Rails 7.0 #43909

DB schema dumper uncompatibility in Rails 7.0 #43909

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Steps to reproduce

Expected behavior

Actual behavior

System configuration