Problem/Motivation

Migration classes are too tightly coupled. In particular, the source, destination, and id map plugins used by the Migration class all contain references to the containing migration, preventing them from being usable apart from the migration. The source coupling is particularly problematic - the builder patch (#2530030: Create the migrate builder plugin type) needs to use the source plugin alone but is forced to construct a dummy migration to do so. Also, in contrib we'd like to implement the migrate-analyze command for analyzing source data from a source plugin - that will also be forced to construct an unnecessary migration to do so.

We recognize that we probably can't accomplish all of this for 8.0 and at least some of it may need to be postponed to 9.0, but having already had some IRC discussions around it we should capture the thinking (not least as a place to point people new to the migration system and asking the same "why-the-hell" questions about this coupling).

Proposed resolution

Tackle the coupling class-by-class.

Remaining tasks

User interface changes

N/A

API changes

Removal of migration injection into the classes it uses. Potential addition of specific bits of information from the migration into those classes.

Data model changes

None anticipated.

Comments

mikeryan’s picture

mikeryan
he/him
Primary language English
Location Pittsfield, MA, USA
commented

Began adding a child issue for decoupling the id map plugin from migrations, but when I came to describe it - "manages the map and message tables for a migration" - maybe it should be tightly coupled?

Version: 8.0.x-dev » 8.1.x-dev

Drupal 8.0.6 was released on April 6 and is the final bugfix release for the Drupal 8.0.x series. Drupal 8.0.x will not receive any further development aside from security fixes. Drupal 8.1.0-rc1 is now available and sites should prepare to update to 8.1.0.

Bug reports should be targeted against the 8.1.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.2.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

mikeryan’s picture

mikeryan
he/him
Primary language English
Location Pittsfield, MA, USA
commented
Version: 8.1.x-dev » 9.x-dev

Apart from the destination child issue, nothing here we plan on pursuing before 9.x.

chx’s picture

chx commented

> Migration classes are too tightly coupled.

That's theory and practically meaningless in this case since some classes will require other Migration specific bits like Row to work.

> In particular, the source, destination, and id map plugins used by the Migration class all contain references to the containing migration, preventing them from being usable apart from the migration.

Good. Aside from source they are unusable anyways on their own and even for source the usage is limited.

So... what's the point and motivation behind this issue?

catch’s picture

catch
he/him
Primary language English
commented
Version: 9.x-dev » 8.3.x-dev

If 9.x only removes backwards compatibility with 8.x and nothing else, then this would need to be done with a backwards compatibility layer. So moving back for now. If it doesn't get done, we can move it back to 9.x when the time comes (but it will probably still need a bc layer then too).

Version: 8.3.x-dev » 8.4.x-dev

Drupal 8.3.0-alpha1 will be released the week of January 30, 2017, which means new developments and disruptive changes should now be targeted against the 8.4.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

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heddn’s picture

heddn
Primary language English
Location Illinois
commented
Version: 8.8.x-dev » 9.x-dev

Realistically speaking, this won't really happen until 9.x (or later).

Version: 9.x-dev » 9.0.x-dev

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xjm’s picture

xjm
she/her
Primary language English
commented
Version: 9.0.x-dev » 9.1.x-dev

This would be a minor-only change since there's additions/deprecations/etc. Since 8.9.x and 9.0.x are now in beta, I'm moving this to 9.1.x. Thanks!

Version: 9.1.x-dev » 9.2.x-dev

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