Custom indexing strategies

Sometimes you want to index "virtual" attributes of an object computed from existing ones, or just want to customize the way certain attributes are indexed, for example, saving only the 10 first characters of a field instead of its whole content.

To do so in an elegant and flexible way, Plone 3.3 includes a new package, plone.indexer, which provides a series of primitives to delegate indexing operations to adapters.

Let's say you have a content-type providing the interface IMyType. To define an indexer for your type which takes the first 10 characters from the body text, just type (assuming the attribute's name is 'text'):

from plone.indexer.decorator import indexer

@indexer(IMyType)
def mytype_description(object, **kw):
     return object.text[:10]

Finally, register this factory function as a named adapter using ZCML. Assuming you've put the code above into a file named indexers.py:

   <adapter name="description" factory=".indexers.mytype_description" />

And that's all! Easy, wasn't it?

Note you can omit the for attribute because you passed this to the @indexer decorator, and you can omit the provides attribute because the thing returned by the decorator is actually a class providing the required IIndexer interface.

To learn more about the plone.indexer package, read its doctest.

For more info about how to create content-types, refer to the Archetypes Developer Manual.

Important note: If you want to adapt a out-of-the-box Archetypes content-type like Event or News Item, take into account you will have to feed the indexer decorator with the Zope 3 interfaces defined in Products.ATContentTypes.interface.* files, not with the deprecated Zope 2 ones into the Products.ATContentTypes.interfaces file.