fix: scope SchemaCreation to IBM_DBAdapter to prevent breaking other adapters

The SchemaCreation class was previously defined by reopening the base
ActiveRecord::ConnectionAdapters::SchemaCreation class directly. This
caused IBM DB2-specific methods (e.g. visit_TableDefinition calling
@conn.servertype) to be invoked for ALL database adapters, not just
IBM DB2 connections.

When an application uses a non-IBM adapter (e.g. PostgreSQL) alongside
the ibm_db gem, Rails' pending migration check triggers the overridden
visit_TableDefinition, which calls @conn.servertype on a
PostgreSQLAdapter instance, raising:

  NoMethodError: undefined method 'servertype' for an instance of
  ActiveRecord::ConnectionAdapters::PostgreSQLAdapter

This fix moves SchemaCreation to be a proper subclass nested inside
IBM_DBAdapter (following the same pattern used by PostgreSQL, MySQL,
and SQLite adapters in Rails) and adds a schema_creation method
override so the IBM-specific SchemaCreation is only used when the
active connection is an IBM DB2 connection.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: lhimo <36077138+lhimo@users.noreply.github.com>

Author: lhimo

IBM_DB_Adapter/ibm_db/lib/active_record/connection_adapters/ibm_db_adapter.rb

@@ -186,113 +186,6 @@ def unique_constraints_in_create(table, stream)
       end
     end
 
-    class SchemaCreation
-      private
-
-      def visit_TableDefinition(o)
-        create_sql = +"CREATE#{table_modifier_in_create(o)} TABLE "
-        create_sql << 'IF NOT EXISTS ' if o.if_not_exists
-        create_sql << "#{quote_table_name(o.name)} "
-
-        statements = o.columns.map { |c| accept c }
-        statements << accept(o.primary_keys) if o.primary_keys
-
-        if supports_indexes_in_create?
-          statements.concat(o.indexes.map { |column_name, options| index_in_create(o.name, column_name, options) })
-        end
-
-        statements.concat(o.foreign_keys.map { |fk| accept fk }) if use_foreign_keys?
-
-        statements.concat(o.check_constraints.map { |chk| accept chk }) if supports_check_constraints?
-
-        @conn.puts_log "visit_TableDefinition #{@conn.servertype}"
-        if !@conn.servertype.instance_of? IBM_IDS
-          statements.concat(o.unique_constraints.map { |exc| accept exc }) if supports_unique_constraints?
-        end
-
-        create_sql << "(#{statements.join(', ')})" if statements.present?
-        add_table_options!(create_sql, o)
-        create_sql << " AS (#{to_sql(o.as)}) WITH DATA" if o.as
-        create_sql
-      end
-
-      def visit_ColumnDefinition(o)
-        if @conn.instance_of? IBM_DBAdapter
-          @conn.puts_log "visit_ColumnDefinition #{o.name} #{o} #{@conn} #{@conn.servertype}"
-        end
-        o.sql_type = type_to_sql(o.type, **o.options)
-        column_sql = +"#{quote_column_name(o.name)} #{o.sql_type}"
-        add_column_options!(column_sql, column_options(o))
-        column_sql
-      end
-
-      def add_column_options!(sql, options)
-        if options_include_default?(options)
-          sql << " DEFAULT #{quote_default_expression(options[:default],
-                                                      options[:column])}"
-        end
-        sql << ' GENERATED BY DEFAULT AS IDENTITY (START WITH 1000)' if options[:auto_increment] == true
-        sql << ' PRIMARY KEY' if options[:primary_key] == true
-        # must explicitly check for :null to allow change_column to work on migrations
-        sql << ' NOT NULL' if options[:null] == false
-        sql
-      end
-
-      def visit_AlterTable(o)
-        sql = +"ALTER TABLE #{quote_table_name(o.name)} "
-        sql << o.adds.map { |col| accept col }.join(" ")
-        sql << o.foreign_key_adds.map { |fk| visit_AddForeignKey fk }.join(" ")
-        sql << o.foreign_key_drops.map { |fk| visit_DropForeignKey fk }.join(" ")
-        sql << o.check_constraint_adds.map { |con| visit_AddCheckConstraint con }.join(" ")
-        sql << o.check_constraint_drops.map { |con| visit_DropCheckConstraint con }.join(" ")
-        sql << o.constraint_validations.map { |fk| visit_ValidateConstraint fk }.join(" ")
-        sql << o.exclusion_constraint_adds.map { |con| visit_AddExclusionConstraint con }.join(" ")
-        sql << o.exclusion_constraint_drops.map { |con| visit_DropExclusionConstraint con }.join(" ")
-        sql << o.unique_constraint_adds.map { |con| visit_AddUniqueConstraint con }.join(" ")
-        sql << o.unique_constraint_drops.map { |con| visit_DropUniqueConstraint con }.join(" ")
-      end
-
-      def visit_ValidateConstraint(name)
-        "VALIDATE CONSTRAINT #{quote_column_name(name)}"
-      end
-
-      def visit_UniqueConstraintDefinition(o)
-        column_name = Array(o.column).map { |column| quote_column_name(column) }.join(", ")
-
-        sql = ["CONSTRAINT"]
-        sql << quote_column_name(o.name)
-        sql << "UNIQUE"
-
-        if o.using_index
-          sql << "USING INDEX #{quote_column_name(o.using_index)}"
-        else
-          sql << "(#{column_name})"
-        end
-
-#        if o.deferrable
-#          sql << "DEFERRABLE INITIALLY #{o.deferrable.to_s.upcase}"
-#        end
-
-        sql.join(" ")
-      end
-
-      def visit_AddExclusionConstraint(o)
-        "ADD #{accept(o)}"
-      end
-
-      def visit_DropExclusionConstraint(name)
-        "DROP CONSTRAINT #{quote_column_name(name)}"
-      end
-
-      def visit_AddUniqueConstraint(o)
-        "ADD #{accept(o)}"
-      end
-
-      def visit_DropUniqueConstraint(name)
-        "DROP CONSTRAINT #{quote_column_name(name)}"
-      end
-
-    end
   end
 
   class Base
@@ -659,6 +552,118 @@ class IBM_DBAdapter < AbstractAdapter
                   :set_quoted_literal_replacement
       attr_accessor :sql, :handle_lobs_triggered, :sql_parameter_values
 
+      # IBM DB2-specific SchemaCreation subclass.
+      # This is scoped to IBM_DBAdapter so it does not interfere with other
+      # adapters (e.g. PostgreSQL, MySQL) that may coexist in the same
+      # application via Rails' multi-database support.
+      class SchemaCreation < ConnectionAdapters::SchemaCreation
+        private
+
+        def visit_TableDefinition(o)
+          create_sql = +"CREATE#{table_modifier_in_create(o)} TABLE "
+          create_sql << 'IF NOT EXISTS ' if o.if_not_exists
+          create_sql << "#{quote_table_name(o.name)} "
+
+          statements = o.columns.map { |c| accept c }
+          statements << accept(o.primary_keys) if o.primary_keys
+
+          if supports_indexes_in_create?
+            statements.concat(o.indexes.map { |column_name, options| index_in_create(o.name, column_name, options) })
+          end
+
+          statements.concat(o.foreign_keys.map { |fk| accept fk }) if use_foreign_keys?
+
+          statements.concat(o.check_constraints.map { |chk| accept chk }) if supports_check_constraints?
+
+          @conn.puts_log "visit_TableDefinition #{@conn.servertype}"
+          if !@conn.servertype.instance_of? IBM_IDS
+            statements.concat(o.unique_constraints.map { |exc| accept exc }) if supports_unique_constraints?
+          end
+
+          create_sql << "(#{statements.join(', ')})" if statements.present?
+          add_table_options!(create_sql, o)
+          create_sql << " AS (#{to_sql(o.as)}) WITH DATA" if o.as
+          create_sql
+        end
+
+        def visit_ColumnDefinition(o)
+          @conn.puts_log "visit_ColumnDefinition #{o.name} #{o} #{@conn} #{@conn.servertype}"
+          o.sql_type = type_to_sql(o.type, **o.options)
+          column_sql = +"#{quote_column_name(o.name)} #{o.sql_type}"
+          add_column_options!(column_sql, column_options(o))
+          column_sql
+        end
+
+        def add_column_options!(sql, options)
+          if options_include_default?(options)
+            sql << " DEFAULT #{quote_default_expression(options[:default],
+                                                        options[:column])}"
+          end
+          sql << ' GENERATED BY DEFAULT AS IDENTITY (START WITH 1000)' if options[:auto_increment] == true
+          sql << ' PRIMARY KEY' if options[:primary_key] == true
+          # must explicitly check for :null to allow change_column to work on migrations
+          sql << ' NOT NULL' if options[:null] == false
+          sql
+        end
+
+        def visit_AlterTable(o)
+          sql = +"ALTER TABLE #{quote_table_name(o.name)} "
+          sql << o.adds.map { |col| accept col }.join(" ")
+          sql << o.foreign_key_adds.map { |fk| visit_AddForeignKey fk }.join(" ")
+          sql << o.foreign_key_drops.map { |fk| visit_DropForeignKey fk }.join(" ")
+          sql << o.check_constraint_adds.map { |con| visit_AddCheckConstraint con }.join(" ")
+          sql << o.check_constraint_drops.map { |con| visit_DropCheckConstraint con }.join(" ")
+          sql << o.constraint_validations.map { |fk| visit_ValidateConstraint fk }.join(" ")
+          sql << o.exclusion_constraint_adds.map { |con| visit_AddExclusionConstraint con }.join(" ")
+          sql << o.exclusion_constraint_drops.map { |con| visit_DropExclusionConstraint con }.join(" ")
+          sql << o.unique_constraint_adds.map { |con| visit_AddUniqueConstraint con }.join(" ")
+          sql << o.unique_constraint_drops.map { |con| visit_DropUniqueConstraint con }.join(" ")
+        end
+
+        def visit_ValidateConstraint(name)
+          "VALIDATE CONSTRAINT #{quote_column_name(name)}"
+        end
+
+        def visit_UniqueConstraintDefinition(o)
+          column_name = Array(o.column).map { |column| quote_column_name(column) }.join(", ")
+
+          sql = ["CONSTRAINT"]
+          sql << quote_column_name(o.name)
+          sql << "UNIQUE"
+
+          if o.using_index
+            sql << "USING INDEX #{quote_column_name(o.using_index)}"
+          else
+            sql << "(#{column_name})"
+          end
+
+          sql.join(" ")
+        end
+
+        def visit_AddExclusionConstraint(o)
+          "ADD #{accept(o)}"
+        end
+
+        def visit_DropExclusionConstraint(name)
+          "DROP CONSTRAINT #{quote_column_name(name)}"
+        end
+
+        def visit_AddUniqueConstraint(o)
+          "ADD #{accept(o)}"
+        end
+
+        def visit_DropUniqueConstraint(name)
+          "DROP CONSTRAINT #{quote_column_name(name)}"
+        end
+      end
+
+      # Returns the IBM DB2-specific SchemaCreation instance, ensuring that
+      # IBM-specific schema methods are only applied to IBM DB2 connections
+      # and do not affect other adapters.
+      def schema_creation # :nodoc:
+        SchemaCreation.new(self)
+      end
+
       # Name of the adapter
       def adapter_name
         'IBM_DB'