#161: Remove migration code for old releases

Contents

1. Motivation
2. Assumptions
3. Proposal
4. Implementation
5. Risks
6. Participants

Proposed by

Hanno Schlichting

Proposal type

Architecture

Assigned to release

• Plone 3.0

State

completed

Motivation

In the process of working on CMF 2.1 support (see PLIP148) I came across a lot of problems due to the old migration code. The two main areas were Action migrations and the content type migration to ATContentTypes.

Assumptions

Migrating to Plone 3 will be possible for all sites that run any released version of Plone 2.1-final, 2.1.x or Plone 2.5. Migrating sites from versions prior to Plone 2.1 can be dealt with easily by migrating to Plone 2.5 first or by doing a new site creation and only upgrading the content in a temporary Plone 2.1/2.5 site. For such old sites it is highly questionable that a direct migration will work anyways as probably all installed add-ons will need new versions and the underlying Zope version will have to make a jump over various versions as well.

Proposal

As I am lazy and would like to save the time to debug all those old problems, fix migration code to work against the new API's and spent my time on more fruitful things instead, I would like to suggest to not support migrations from prior to Plone 2.1.0-final to Plone 3.0.

I think as we have no real migration tests at all, trying to support age-old migration code is more of a burden and risky then it is beneficial. The number of people actually trying to upgrade from a pre 2.1 version to Plone 3 will most likely be rather small anyways. For these sites creating a new site based on Plone 3 and only importing the content is probably a more reliable way and we should advertise it instead of telling those people to do an inline migration which will reindex their content probably a few dozen times ;)

Implementation

The implementation is pretty simple. Just remove all the migrations from Plone itself and ATContentTypes.

Risks

Some people might try to migrate to Plone 3 directly but we can provide a nice error message in these cases telling them that directly migrating isn't supported anymore and pointing them to the 2.5 release which they should migrate to first.

Participants

Hanno Schlichting