diff --git a/Gemfile b/Gemfile
index efc42360b..d3fe4f902 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,6 +2,7 @@ source 'http://rubygems.org'
 
 gem 'mysql2', '0.2.6'
 #gem 'pg'
+#gem 'sqlite3'
 gem 'rails', '3.0.3'
 gem 'foreigner', '0.9.1'
 
diff --git a/app/models/aspect_membership.rb b/app/models/aspect_membership.rb
index 163dc6182..372e744ea 100644
--- a/app/models/aspect_membership.rb
+++ b/app/models/aspect_membership.rb
@@ -10,7 +10,7 @@ class AspectMembership < ActiveRecord::Base
   has_one :person, :through => :contact
 
   before_destroy do
-    if self.contact.aspects.size == 1
+    if self.contact && self.contact.aspects.size == 1
       self.user.disconnect(self.contact)
     end
     true
diff --git a/app/models/notification.rb b/app/models/notification.rb
index 7fceff2a8..167cad1a6 100644
--- a/app/models/notification.rb
+++ b/app/models/notification.rb
@@ -7,7 +7,7 @@ class Notification < ActiveRecord::Base
   include Diaspora::Socketable
 
   belongs_to :recipient, :class_name => 'User'
-  has_many :notification_actors
+  has_many :notification_actors, :dependent => :destroy
   has_many :actors, :class_name => 'Person', :through => :notification_actors, :source => :person
   belongs_to :target, :polymorphic => true
 
diff --git a/app/models/person.rb b/app/models/person.rb
index 0f93cd4c7..b59437b78 100644
--- a/app/models/person.rb
+++ b/app/models/person.rb
@@ -17,7 +17,7 @@ class Person < ActiveRecord::Base
   xml_attr :profile, :as => Profile
   xml_attr :exported_key
 
-  has_one :profile
+  has_one :profile, :dependent => :destroy
   delegate :last_name, :to => :profile
 
   before_validation :downcase_diaspora_handle
@@ -25,8 +25,9 @@ class Person < ActiveRecord::Base
     diaspora_handle.downcase! unless diaspora_handle.blank?
   end
 
-  has_many :contacts #Other people's contacts for this person
-  has_many :posts, :foreign_key => :author_id #his own posts
+  has_many :contacts, :dependent => :destroy #Other people's contacts for this person
+  has_many :posts, :foreign_key => :author_id, :dependent => :destroy #his own posts
+  has_many :comments, :foreign_key => :author_id, :dependent => :destroy #his own comments
 
   belongs_to :owner, :class_name => 'User'
 
diff --git a/app/models/post.rb b/app/models/post.rb
index 72651977d..722c5a724 100644
--- a/app/models/post.rb
+++ b/app/models/post.rb
@@ -13,7 +13,7 @@ class Post < ActiveRecord::Base
   xml_attr :public
   xml_attr :created_at
 
-  has_many :comments, :order => 'created_at ASC'
+  has_many :comments, :order => 'created_at ASC', :dependent => :destroy
   has_many :likes, :conditions => {:positive => true}, :dependent => :delete_all
   has_many :dislikes, :conditions => {:positive => false}, :class_name => 'Like', :dependent => :delete_all
 
diff --git a/app/models/user.rb b/app/models/user.rb
index a0155bcbc..3d46d7a88 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -31,14 +31,14 @@ class User < ActiveRecord::Base
   has_one :person, :foreign_key => :owner_id
   delegate :public_key, :posts, :owns?, :diaspora_handle, :name, :public_url, :profile, :first_name, :last_name, :to => :person
 
-  has_many :invitations_from_me, :class_name => 'Invitation', :foreign_key => :sender_id
-  has_many :invitations_to_me, :class_name => 'Invitation', :foreign_key => :recipient_id
+  has_many :invitations_from_me, :class_name => 'Invitation', :foreign_key => :sender_id, :dependent => :destroy
+  has_many :invitations_to_me, :class_name => 'Invitation', :foreign_key => :recipient_id, :dependent => :destroy
   has_many :aspects
   has_many :aspect_memberships, :through => :aspects
   has_many :contacts
   has_many :contact_people, :through => :contacts, :source => :person
-  has_many :services
-  has_many :user_preferences
+  has_many :services, :dependent => :destroy
+  has_many :user_preferences, :dependent => :destroy
 
   before_save do
     person.save if person && person.changed?