ruby - Updating a property set as the key in DataMapper -

is possible update property in datamapper if :key set true?

say, example, have model set this:

class post   include datamapper::resource   property :slug, text, :unique => true, :key => true   # ... end 

and made new instance of :slug => "example-post-title".

i tried update accessing stored

@post = post.get("example-post-title") #=> #<post @slug="example-post-title" ...> @post.slug = "example-post-title-2" #=> "example-post-title-2" @post.save #=> true @post = post.get("example-post-title-2") #=> nil 

but can see slug never updated. tried using post#update method:

@post = post.get("example-post-title") #=> #<post @slug="example-post-title" ...> @post.update(:slug => "example-post-title-2") #=> true @post = post.get("example-post-title-2") #=> nil 

looking in database, index column not changed either of these examples. remains example-post-title rather example-post-title-2.

according docs, post#update method, similar post#save method, should return true if operation successful, , false if not. returning true here, it's not updating record.

i've searched , searched , can't find on internet. neither stackoverflow nor datamapper rdoc had updating key.

i know can have unique serial property , instances of post using slug (as in, make serial property key instead of slug), i'm looking way without that, if @ possible.

my hunch can't update key. according doc, protected against mass assignment:

natural keys protected against mass-assignment, setter= need called individually if you're looking set them.

they don't talk updating them in "key => value" stores impossible or deprecated update key. i'd assume that's case here well, though can't find hard evidence give : /