Add AbstractAdapter#table_alias_for to create table aliases according to the rules of the current adapter. [Rick]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@3916 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

7 files changed, 43 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index d80109b16d..668df3698f 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Add AbstractAdapter#table_alias_for to create table aliases according to the rules of the current adapter. [Rick]
+
 * Provide access to the underlying database connection through Adapter#raw_connection. Enables the use of db-specific methods without complicating the adapters. #2090 [Koz]
 
 * Remove broken attempts at handling columns with a default of 'now()' in the postgresql adapter. #2257 [Koz]
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 76967c0fe0..d0b8a1ba1c 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -8,6 +8,20 @@ module ActiveRecord
         {}
       end
 
+      # This is the maximum length a table alias can be
+      def table_alias_length
+        255
+      end
+
+      # Truncates a table alias according to the limits of the current adapter.  
+      def table_alias_for(table_name, index = 1)
+        if index > 1
+          "#{table_name[0..table_alias_length-3]}_#{index}"
+        else
+          table_name[0..table_alias_length-1]
+        end
+      end
+
       # def tables(name = nil) end
 
       # Returns an array of indexes for the given table.
diff --git a/activerecord/lib/active_record/connection_adapters/db2_adapter.rb b/activerecord/lib/active_record/connection_adapters/db2_adapter.rb
index 06c13c39ad..9819c5a92a 100644
--- a/activerecord/lib/active_record/connection_adapters/db2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/db2_adapter.rb
@@ -188,6 +188,10 @@ begin
         def reconnect!
         end
 
+        def table_alias_length
+          128
+        end
+
         private
 
         def with_statement
diff --git a/activerecord/lib/active_record/connection_adapters/oracle_adapter.rb b/activerecord/lib/active_record/connection_adapters/oracle_adapter.rb
index 3291fac455..c34b3596df 100644
--- a/activerecord/lib/active_record/connection_adapters/oracle_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/oracle_adapter.rb
@@ -191,6 +191,9 @@ begin
           }
         end
 
+        def table_alias_length
+          30
+        end
 
         # QUOTING ==================================================
         #
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 354df9a42e..53f47b2ad6 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -101,6 +101,9 @@ module ActiveRecord
         true
       end      
       
+      def table_alias_length
+        63
+      end
 
       # QUOTING ==================================================
 
diff --git a/activerecord/lib/active_record/connection_adapters/sybase_adapter.rb b/activerecord/lib/active_record/connection_adapters/sybase_adapter.rb
index 67d1c368eb..75a0b4ed18 100644
--- a/activerecord/lib/active_record/connection_adapters/sybase_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sybase_adapter.rb
@@ -150,6 +150,10 @@ module ActiveRecord
         # connect! # Not yet implemented
       end
 
+      def table_alias_length
+        30
+      end
+
       # Check for a limit statement and parse out the limit and
       # offset if specified. Remove the limit from the sql statement
       # and call select.
diff --git a/activerecord/test/adapter_test.rb b/activerecord/test/adapter_test.rb
index af76ebfc9a..2c98045cee 100644
--- a/activerecord/test/adapter_test.rb
+++ b/activerecord/test/adapter_test.rb
@@ -46,6 +46,19 @@ class AdapterTest < Test::Unit::TestCase
     end
   end
 
+  def test_table_alias
+    old = @connection.table_alias_length
+    def @connection.table_alias_length() 10; end
+      
+    assert_equal 'posts',      @connection.table_alias_for('posts')
+    assert_equal 'posts',      @connection.table_alias_for('posts', 1)
+    assert_equal 'posts_2',    @connection.table_alias_for('posts', 2)
+    assert_equal 'posts_comm', @connection.table_alias_for('posts_comments')
+    assert_equal 'posts_co_2', @connection.table_alias_for('posts_comments', 2)
+    
+    def @connection.table_alias_length() old; end
+  end
+
   # test resetting sequences in odd tables in postgreSQL
   if ActiveRecord::Base.connection.respond_to?(:reset_pk_sequence!)
     require 'fixtures/movie'