Don't drop tables if they already exist

demo-site/models.rb

@@ -7,13 +7,16 @@
 DB = Sequel.connect(ENV['DATABASE_URL'] || 'sqlite:/')
 DB.loggers << Logger.new($stdout) unless DEMO_MODE
 
-DB.create_table!(:artists) do
+unless DB.table_exists?(:artists)
+DB.create_table(:artists) do
   primary_key :id
   String :name, :null=>false, :unique=>true
 end
 1.upto(3){|x| DB[:artists].insert(:name=>"Example Artist #{x}")}
+end
 
-DB.create_table!(:albums) do
+unless DB.table_exists?(:albums)
+DB.create_table(:albums) do
   primary_key :id
   String :name, :null=>false
   foreign_key :artist_id, :artists, :null=>false
@@ -25,8 +28,10 @@
   index [:name, :artist_id], :unique=>true
 end
 DB[:albums].insert(:name=>'Example Album', :artist_id=>1, :release_date=>'1979-01-02', :release_party_time=>'1979-01-03 04:05:06', :debut_album=>true, :out_of_print=>false)
+end
 
-DB.create_table!(:tracks) do
+unless DB.table_exists?(:tracks)
+DB.create_table(:tracks) do
   primary_key :id
   Integer :number, :null=>false
   String :name, :null=>false
@@ -37,20 +42,25 @@
 DB[:tracks].insert(:name=>'Example Track 2', :number=>2, :album_id=>1, :length=>6.4)
 DB[:tracks].insert(:name=>'Example Track 3', :number=>1, :length=>0.1)
 DB[:tracks].insert(:name=>'Example Track 4', :number=>2, :length=>0.2)
+end
 
-DB.create_table!(:tags) do
+unless DB.table_exists?(:tags)
+DB.create_table(:tags) do
   primary_key :id
   String :name, :null=>false, :unique=>true
 end
 1.upto(3){|x| DB[:tags].insert(:name=>"Example Tag #{x}")}
+end
 
-DB.create_table!(:albums_tags) do
+unless DB.table_exists?(:albums_tags)
+DB.create_table(:albums_tags) do
   foreign_key :album_id, :albums
   foreign_key :tag_id, :tags
   primary_key [:album_id, :tag_id]
 end
 DB[:albums_tags].insert(1, 1)
 DB[:albums_tags].insert(1, 2)
+end
 
 Sequel::Model.plugin :defaults_setter
 Sequel::Model.plugin :forme