This uses a DSL which is inspired by DataMapper, but also ActiveRecord. In addition, many of its Core Date related design principles are based on MagicalRecord.
The following models define a schema that is immediatly available during development:
class Author < MotionData::ManagedObject hasMany :articles, :class => 'Article', :inverse => :author property :name, String, :required => true end class Article < MotionData::ManagedObject belongsTo :author, :class => 'Author', :inverse => :articles property :title, String, :required => true property :body, String, :required => true property :published, Boolean, :default => false end
The Schema instance can dump this definition, which looks like:
Schema.defineVersion('1.0') do |s| s.addEntity do |e| e.name = 'Article' e.managedObjectClassName = 'Article' e.addProperty :published, Boolean, {:default=>false} e.addProperty :title, String, {:required=>true} e.addProperty :body, String, {:required=>true} end s.addEntity do |e| e.name = 'Author' e.managedObjectClassName = 'Author' e.addProperty :name, String, {:required=>true} end end
As you can see it has a version, this is the app’s release version. These dumps would be created on each new release of the app and would then allow for easy migrations with code that can be found in @mdiep’s CoreDataInCode example.
MotionData provides ‘finder scopes’, which are conceptually the same as those in ActiveRecord.
For instance, to select a subset of an entity’s to-many association:
author.articles.where(:published => true) author.articles.where(:published => true).sortBy(:title)
Or for predicates that are more elaborate than simple AND condtitions, you
can use a predicate builder proxy:
author.articles.where(value(:body) != nil).and(value(:body) != nil)
Finally, in case you need to create a typical NSPredicate, you can do that
too and pass the instance to where, or create one with where:
author.articles.where('body != %@ AND published == %@', nil, true)
The query builder methods that can be found in the ‘dynamic scopes’ section, can also be ‘saved’ on the model:
class Article scope :published, where(:published => true) scope :valid, where(value(:body) != nil) end
This makes these scopes available to query all of a model’s entities:
Article.published.valid
Or on a to-many association:
author.articles.published.valid