Merge pull request rails#53797 from fatkodima/change-structure-dump-versions-ordering

Introduce versions formatter for the schema dumper

Author: byroot

activerecord/CHANGELOG.md

@@ -1,3 +1,14 @@
+*   Introduce versions formatter for the schema dumper.
+
+    It is now possible to override how schema dumper formats versions information inside the
+    `structure.sql` file. Currently, the versions are simply sorted in the decreasing order.
+    Within large teams, this can potentially cause many merge conflicts near the top of the list.
+
+    Now, the custom formatter can be provided with a custom sorting logic (e.g. by hash values
+    of the versions), which can greatly reduce the number of conflicts.
+
+    *fatkodima*
+
 *   Serialized attributes can now be marked as comparable.
 
     A not rare issue when working with serialized attributes is that the serialized representation of an object

activerecord/lib/active_record.rb

@@ -403,6 +403,12 @@ def self.permanent_connection_checkout=(value)
   singleton_class.attr_accessor :migration_strategy
   self.migration_strategy = Migration::DefaultStrategy
 
+  ##
+  # :singleton-method: schema_versions_formatter
+  # Specify the formatter used by schema dumper to format versions information.
+  singleton_class.attr_accessor :schema_versions_formatter
+  self.schema_versions_formatter = Migration::DefaultSchemaVersionsFormatter
+
   ##
   # :singleton-method: dump_schema_after_migration
   # Specify whether schema dump should happen at the end of the

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -1353,7 +1353,7 @@ def remove_constraint(table_name, constraint_name) # :nodoc:
         execute schema_creation.accept(at)
       end
 
-      def dump_schema_information # :nodoc:
+      def dump_schema_versions # :nodoc:
         versions = pool.schema_migration.versions
         insert_versions_sql(versions) if versions.any?
       end
@@ -1876,16 +1876,8 @@ def remove_timestamps_for_alter(table_name, **options)
         end
 
         def insert_versions_sql(versions)
-          sm_table = quote_table_name(pool.schema_migration.table_name)
-
-          if versions.is_a?(Array)
-            sql = +"INSERT INTO #{sm_table} (version) VALUES\n"
-            sql << versions.reverse.map { |v| "(#{quote(v)})" }.join(",\n")
-            sql << ";"
-            sql
-          else
-            "INSERT INTO #{sm_table} (version) VALUES (#{quote(versions)});"
-          end
+          versions_formatter = ActiveRecord.schema_versions_formatter.new(self)
+          versions_formatter.format(versions)
         end
 
         def data_source_sql(name = nil, type: nil)

activerecord/lib/active_record/migration.rb

@@ -571,6 +571,7 @@ def initialize
   class Migration
     autoload :CommandRecorder, "active_record/migration/command_recorder"
     autoload :Compatibility, "active_record/migration/compatibility"
+    autoload :DefaultSchemaVersionsFormatter, "active_record/migration/default_schema_versions_formatter"
     autoload :JoinTable, "active_record/migration/join_table"
     autoload :ExecutionStrategy, "active_record/migration/execution_strategy"
     autoload :DefaultStrategy, "active_record/migration/default_strategy"

activerecord/lib/active_record/migration/default_schema_versions_formatter.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class Migration
+    # This class is used by the schema dumper to format versions information.
+    #
+    # The class receives the current +connection+ when initialized.
+    class DefaultSchemaVersionsFormatter # :nodoc:
+      def initialize(connection)
+        @connection = connection
+      end
+
+      def format(versions)
+        sm_table = connection.quote_table_name(connection.pool.schema_migration.table_name)
+
+        if versions.is_a?(Array)
+          sql = +"INSERT INTO #{sm_table} (version) VALUES\n"
+          sql << versions.reverse.map { |v| "(#{connection.quote(v)})" }.join(",\n")
+          sql << ";"
+          sql
+        else
+          "INSERT INTO #{sm_table} (version) VALUES (#{connection.quote(versions)});"
+        end
+      end
+
+      private
+        attr_reader :connection
+    end
+  end
+end

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -445,7 +445,7 @@ def dump_schema(db_config, format = ActiveRecord.schema_format) # :nodoc:
           structure_dump(db_config, filename)
           if migration_connection_pool.schema_migration.table_exists?
             File.open(filename, "a") do |f|
-              f.puts migration_connection.dump_schema_information
+              f.puts migration_connection.dump_schema_versions
               f.print "\n"
             end
           end

activerecord/test/cases/schema_dumper_test.rb

@@ -18,19 +18,19 @@ def standard_dump
     @@standard_dump ||= dump_all_table_schema
   end
 
-  def test_dump_schema_information_with_empty_versions
+  def test_dump_schema_versions_with_empty_versions
     @schema_migration.delete_all_versions
-    schema_info = ActiveRecord::Base.lease_connection.dump_schema_information
+    schema_info = ActiveRecord::Base.lease_connection.dump_schema_versions
     assert_no_match(/INSERT INTO/, schema_info)
   end
 
-  def test_dump_schema_information_outputs_lexically_reverse_ordered_versions_regardless_of_database_order
+  def test_dump_schema_versions_outputs_lexically_reverse_ordered_versions_regardless_of_database_order
     versions = %w{ 20100101010101 20100201010101 20100301010101 }
     versions.shuffle.each do |v|
       @schema_migration.create_version(v)
     end
 
-    schema_info = ActiveRecord::Base.lease_connection.dump_schema_information
+    schema_info = ActiveRecord::Base.lease_connection.dump_schema_versions
     expected = <<~STR
     INSERT INTO #{quote_table_name("schema_migrations")} (version) VALUES
     ('20100301010101'),

guides/source/configuring.md

@@ -1205,6 +1205,27 @@ end
 config.active_record.migration_strategy = CustomMigrationStrategy
 ```
 
+#### `config.active_record.schema_versions_formatter`
+
+Controls the formatter class used by schema dumper to format versions information. Custom class can be provided
+to change the default behavior:
+
+```ruby
+class CustomSchemaVersionsFormatter
+  def format(versions)
+    # Special sorting of versions to reduce the likelihood of conflicts.
+    sorted_versions = versions.sort { |a, b| b.to_s.reverse <=> a.to_s.reverse }
+
+    sql = +"INSERT INTO schema_migrations (version) VALUES\n"
+    sql << sorted_versions.map { |v| "(#{connection.quote(v)})" }.join(",\n")
+    sql << ";"
+    sql
+  end
+end
+
+config.active_record.schema_versions_formatter = CustomSchemaVersionsFormatter
+```
+
 #### `config.active_record.lock_optimistically`
 
 Controls whether Active Record will use optimistic locking and is `true` by default.