Revert "Revert "Add index length support for MySQL [#1852 state:open]""

This reverts commit 6626833db13a69786f9f6cd56b9f53c4017c3e39.

4 files changed, 38 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 6c477e48ce..e42cd99786 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -258,7 +258,7 @@ module ActiveRecord
         end
     end
 
-    class IndexDefinition < Struct.new(:table, :name, :unique, :columns) #:nodoc:
+    class IndexDefinition < Struct.new(:table, :name, :unique, :columns, :lengths) #:nodoc:
     end
 
     # Abstract representation of a column definition. Instances of this type
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 e8cba1bd41..1255ef09be 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -256,18 +256,32 @@ module ActiveRecord
       # name.
       #
       # ===== Examples
+      #
       # ====== Creating a simple index
       #  add_index(:suppliers, :name)
       # generates
       #  CREATE INDEX suppliers_name_index ON suppliers(name)
+      #
       # ====== Creating a unique index
       #  add_index(:accounts, [:branch_id, :party_id], :unique => true)
       # generates
       #  CREATE UNIQUE INDEX accounts_branch_id_party_id_index ON accounts(branch_id, party_id)
+      #
       # ====== Creating a named index
       #  add_index(:accounts, [:branch_id, :party_id], :unique => true, :name => 'by_branch_party')
       # generates
       #  CREATE UNIQUE INDEX by_branch_party ON accounts(branch_id, party_id)
+      #
+      # ====== Creating an index with specific key length
+      #  add_index(:accounts, :name, :name => 'by_name', :length => 10)
+      # generates
+      #  CREATE INDEX by_name ON accounts(name(10))
+      #
+      #  add_index(:accounts, [:name, :surname], :name => 'by_name_surname', :length => {:name => 10, :surname => 15})
+      # generates
+      #  CREATE INDEX by_name_surname ON accounts(name(10), surname(15))
+      #
+      # Note: SQLite doesn't support index length
       def add_index(table_name, column_name, options = {})
         column_names = Array.wrap(column_name)
         index_name   = index_name(table_name, :column => column_names)
@@ -278,7 +292,9 @@ module ActiveRecord
         else
           index_type = options
         end
-        quoted_column_names = column_names.map { |e| quote_column_name(e) }.join(", ")
+
+        quoted_column_names = quoted_columns_for_index(column_names, options).join(", ")
+
         execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{quoted_column_names})"
       end
 
@@ -430,6 +446,11 @@ module ActiveRecord
       end
 
       protected
+        # Overridden by the mysql adapter for supporting index lengths
+        def quoted_columns_for_index(column_names, options = {})
+          column_names.map {|name| quote_column_name(name) }
+        end
+
         def options_include_default?(options)
           options.include?(:default) && !(options[:null] == false && options[:default].nil?)
         end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 55d9d20bb5..470ff8d767 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -461,10 +461,11 @@ module ActiveRecord
           if current_index != row[2]
             next if row[2] == "PRIMARY" # skip the primary key
             current_index = row[2]
-            indexes << IndexDefinition.new(row[0], row[2], row[1] == "0", [])
+            indexes << IndexDefinition.new(row[0], row[2], row[1] == "0", [], [])
           end
 
           indexes.last.columns << row[4]
+          indexes.last.lengths << row[7]
         end
         result.free
         indexes
@@ -594,6 +595,18 @@ module ActiveRecord
       end
 
       protected
+        def quoted_columns_for_index(column_names, options = {})
+          length = options[:length] if options.is_a?(Hash)
+
+          quoted_column_names = case length
+          when Hash
+            column_names.map {|name| length[name] ? "#{quote_column_name(name)}(#{length[name]})" : quote_column_name(name) }
+          when Fixnum
+            column_names.map {|name| "#{quote_column_name(name)}(#{length})"}
+          else
+            column_names.map {|name| quote_column_name(name) }
+          end
+        end
 
         def translate_exception(exception, message)
           return super unless exception.respond_to?(:errno)
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index c8e1b4f53a..5cb639a300 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -177,6 +177,7 @@ HEADER
             statment_parts << index.columns.inspect
             statment_parts << (':name => ' + index.name.inspect)
             statment_parts << ':unique => true' if index.unique
+            statment_parts << (':length => ' + Hash[*index.columns.zip(index.lengths).flatten].inspect) if index.lengths.compact.present?
 
             '  ' + statment_parts.join(', ')
           end