• Launchpad entry: https://blueprints.edge.launchpad.net/launchpad/+spec/pillar-alias

• Created: 2007-12-07 by FrancisJLacoste

• Contributors:

Summary

We want to add aliases to our pillars. To achieve this, we'll add an 'aliases' column on our pillars tables: Distribution, Product, Project. Launchpad administrators will be able to modify that field, and triggers will maintain automatically the PillarName table.

Release Note

Launchpad now supports project aliases. If one of your project is well known on another alias, file a question on the Launchpad project stating your project and the aliases you'd like.

Rationale

Some projects are known under many names. Restricting projects to only one name makes users register project on the other names. This would also be useful for migration purpose.

Use cases

• The Gaim was renamed to Pidgin. Its maintainer renames his project from 'gaim' to 'pidgin' and asks that an alias for 'gaim' be maintained.
• Many users tries to register the 'postgres' project. That project is already registered under 'postgresql'. A Launchpad administrator adds the common 'postgres' alias to this project.

Assumptions

We are not doing automatic alias creation on renaming because the main use-case for allowing project renaming is to free up the namespace.

Design

Since our namespace is maintained in the PillarName, aliases need to appear in that table. Since this table is automatically maintained using trigger, it makes sense that the aliases are also added automatically based on an aliases column in the distribution, project, and product tables.

Since aliases could cause land-grab abuses, modifying the aliases of a project will be restricted to Launchpad administrators.

This is only to make aliases work on the web app; we need to do changes in other places to make it possible for bzr to access branches using a product's alias. After discussion with Aaron, it seems like we have two options.

1. Update our xmlrpc to dereference lp: URLs using a product's alias, thus giving the branch's canonical URL to bzr.
2. Supporting the aliases on the codehosting system, probably through redirects. The problem, though, as pointed by Aaron is that doing redirects properly for bzr+ssh or sftp requires a new bzr format, and work on the twisted server; improperly just requires twisted work. Either way it's some considerable work.

We decided to nor implement this in the first round. If needed, it can obviously implemented later.

Implementation

UI Changes

Launchpad administrators visiting the 'Edit details' page of distributions, products and projects will see a simple text field called 'Aliases'.

Code Changes

We'll need to modify the Launchpad navigation to redirect to the base pillar name if a URL uses an alias. This can be done simply using:

•     # Pillar accessed through one of its aliases
      if pillar.name != name:
          self.redirectSubTree(canonical_url(pillar), status=301)

The PillarNameSet.search() method will also need to be modified so that the aliases are considered for exact name matching.

Branch navigation will also need to do this redirection.

We'll add a getCanonicalName() to IPillarName. That method will return the canonical name or self if called on the canonical one.

We may add a getCanonical() method on IPillarName which would retrieve the canonical PillarName or self, when it's the canonical one.

IPillar

A new IPillar will be defined. It will provide the following attributes:

•     class IPillar(Interface):
      
          name = PillarNameField(
              title = _('Name'),
              description=_('The pillar canonical name.'),
              constraint=name_validator,
              required=True, readonly=True)
          
          aliases = Attribute('Sequence of aliases name for this pillar.')
  
          def addAlias(name):
              """Adds an alias to this pillar.
  
              :raises AliasAlreadyDefinedError: if the name is already taken.
              """
  
          def removeAlias(name):
              """Removes an alias from this pillar.
  
              :raises NotFoundError: if the alias isn't defined.
              """

UI Changes

A field to edit the aliases will be added to the 'Edit details' of distribution, project and product. That field will be a simple text field containing a white-space delimited list of aliases name. Editing of that field will be restricted to Launchpad administrators.

Schema Changes

We'll add an alias column to the PillarName name.

• ALTER TABLE PillarName ADD COLUMN alias_for integer;
  ALTER TABLE PillarName ADD CONSTRAINT pillarname__alias_for__fk
      FOREIGN KEY (alias_for) REFERENCES PillarName;
  CREATE INDEX pillarname__alias_for__idx ON PillarName(alias_for)
      WHERE alias_for IS NOT NULL;
  
  ALTER TABLE PillarName DROP CONSTRAINT only_one_target;

We'll need to drop the constraint on PillarName that only one name exists for each pillar (distribution, product, project).

The trigger will also need to be modified to cope with the fact that more than one pillarname may be associated with a pillar. What trigger? ElliotMurphy

Migration

No migration is necessary.