change methods call from contexts

app/models/collections/context.rb

 module Collections
   class Context
-    attr_reader :from, :privacy
 
-    def initialize
-      @from = nil
-      @privacy = nil
+    def from
+      raise NotImplementedError, 'This method must be implemented'
+    end
+
+    def privacy
+      raise NotImplementedError, 'This method must be implemented'
     end
 
   end

app/models/collections/public_context.rb

@@ -3,9 +3,12 @@
 # The PublicContext class specify all collections with field privacy=public
 class Collections::PublicContext < Collections::Context
 
-  def initialize
-    @from = 'Collection'
-    @privacy = 'public'
+  def from
+    'Collection'
+  end
+
+  def privacy
+    'public'
   end
 
 end
\ No newline at end of file

app/models/collections/user_context.rb

@@ -2,7 +2,10 @@ class UserContext < Collections::Context
 
   def initialize(user)
     @user = user
-    @from = sprintf "select expand(in('BelongsTo')) from %s)", user.rid
+  end
+
+  def from
+    sprintf "select expand(in('BelongsTo')) from %s)", @user.rid
   end
 
 end
\ No newline at end of file

app/models/collections/user_private_context.rb

@@ -4,7 +4,7 @@
 class Collections::UserPrivateContext < Collections::UserContext
 
   def privacy
-    @privacy = 'private'
+    'private'
   end
 
 end
\ No newline at end of file

app/models/collections/user_public_context.rb

@@ -4,7 +4,7 @@
 class Collections::UserPublicContext < Collections::UserContext
 
   def privacy
-    @privacy = 'public'
+    'public'
   end
 
 end
\ No newline at end of file