Database comments: Treat blank comments as no comment. Don't dump blank comments.

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

@@ -46,7 +46,7 @@ def prepare_column_options(column)
           spec[:collation] = collation
         end
 
-        spec[:comment] = column.comment.inspect if column.comment
+        spec[:comment] = column.comment.inspect if column.comment.present?
 
         spec
       end

activerecord/lib/active_record/schema_dumper.rb

@@ -138,7 +138,7 @@ def table(table, stream)
           table_options = @connection.table_options(table)
           tbl.print ", options: #{table_options.inspect}" unless table_options.blank?
 
-          if comment = @connection.table_comment(table)
+          if comment = @connection.table_comment(table).presence
             tbl.print ", comment: #{comment.inspect}"
           end
 

activerecord/test/cases/comment_test.rb

 require 'cases/helper'
 require 'support/schema_dumping_helper'
 
+if ActiveRecord::Base.connection.supports_comments?
+
 class CommentTest < ActiveRecord::TestCase
   include SchemaDumpingHelper
   self.use_transactional_tests = false if current_adapter?(:Mysql2Adapter)
@@ -9,81 +11,120 @@ class Commented < ActiveRecord::Base
     self.table_name = 'commenteds'
   end
 
-  def setup
+  class BlankComment < ActiveRecord::Base
+  end
+
+  setup do
     @connection = ActiveRecord::Base.connection
 
-    @connection.transaction do
-      @connection.create_table('commenteds', comment: 'A table with comment', force: true) do |t|
-        t.string  'name',    comment: 'Comment should help clarify the column purpose'
-        t.boolean 'obvious', comment: 'Question is: should you comment obviously named objects?'
-        t.string  'content'
-        t.index   'name',    comment: %Q["Very important" index that powers all the performance.\nAnd it's fun!]
-      end
+    @connection.create_table('commenteds', comment: 'A table with comment', force: true) do |t|
+      t.string  'name',    comment: 'Comment should help clarify the column purpose'
+      t.boolean 'obvious', comment: 'Question is: should you comment obviously named objects?'
+      t.string  'content'
+      t.index   'name',    comment: %Q["Very important" index that powers all the performance.\nAnd it's fun!]
+    end
+
+    @connection.create_table('blank_comments', comment: ' ', force: true) do |t|
+      t.string :space_comment, comment: ' '
+      t.string :empty_comment, comment: ''
+      t.string :nil_comment, comment: nil
+      t.string :absent_comment
     end
+
+    Commented.reset_column_information
+    BlankComment.reset_column_information
   end
 
   teardown do
     @connection.drop_table 'commenteds', if_exists: true
+    @connection.drop_table 'blank_comments', if_exists: true
+  end
+
+  def test_column_created_in_block
+    column = Commented.columns_hash['name']
+    assert_equal :string, column.type
+    assert_equal 'Comment should help clarify the column purpose', column.comment
   end
 
-  if ActiveRecord::Base.connection.supports_comments?
-    def test_column_created_in_block
-      Commented.reset_column_information
-      column = Commented.columns_hash['name']
+  def test_blank_columns_created_in_block
+    %w[ space_comment empty_comment nil_comment absent_comment ].each do |field|
+      column = BlankComment.columns_hash[field]
       assert_equal :string, column.type
-      assert_equal 'Comment should help clarify the column purpose', column.comment
+      assert_nil column.comment
     end
+  end
 
-    def test_add_column_with_comment_later
-      @connection.add_column :commenteds, :rating, :integer, comment: 'I am running out of imagination'
-      Commented.reset_column_information
-      column = Commented.columns_hash['rating']
+  def test_add_column_with_comment_later
+    @connection.add_column :commenteds, :rating, :integer, comment: 'I am running out of imagination'
+    Commented.reset_column_information
+    column = Commented.columns_hash['rating']
 
-      assert_equal :integer, column.type
-      assert_equal 'I am running out of imagination', column.comment
-    end
+    assert_equal :integer, column.type
+    assert_equal 'I am running out of imagination', column.comment
+  end
 
-    def test_add_index_with_comment_later
-      @connection.add_index :commenteds, :obvious, name: 'idx_obvious', comment: 'We need to see obvious comments'
-      index = @connection.indexes('commenteds').find { |idef| idef.name == 'idx_obvious' }
-      assert_equal 'We need to see obvious comments', index.comment
-    end
+  def test_add_index_with_comment_later
+    @connection.add_index :commenteds, :obvious, name: 'idx_obvious', comment: 'We need to see obvious comments'
+    index = @connection.indexes('commenteds').find { |idef| idef.name == 'idx_obvious' }
+    assert_equal 'We need to see obvious comments', index.comment
+  end
 
-    def test_add_comment_to_column
-      @connection.change_column :commenteds, :content, :string, comment: 'Whoa, content describes itself!'
+  def test_add_comment_to_column
+    @connection.change_column :commenteds, :content, :string, comment: 'Whoa, content describes itself!'
 
-      Commented.reset_column_information
-      column = Commented.columns_hash['content']
+    Commented.reset_column_information
+    column = Commented.columns_hash['content']
 
-      assert_equal :string, column.type
-      assert_equal 'Whoa, content describes itself!', column.comment
-    end
+    assert_equal :string, column.type
+    assert_equal 'Whoa, content describes itself!', column.comment
+  end
 
-    def test_remove_comment_from_column
-      @connection.change_column :commenteds, :obvious, :string, comment: nil
+  def test_remove_comment_from_column
+    @connection.change_column :commenteds, :obvious, :string, comment: nil
 
-      Commented.reset_column_information
-      column = Commented.columns_hash['obvious']
+    Commented.reset_column_information
+    column = Commented.columns_hash['obvious']
 
-      assert_equal :string, column.type
-      assert_nil column.comment
-    end
+    assert_equal :string, column.type
+    assert_nil column.comment
+  end
 
-    def test_schema_dump_with_comments
-      # Do all the stuff from other tests
-      @connection.add_column    :commenteds, :rating, :integer, comment: 'I am running out of imagination'
-      @connection.change_column :commenteds, :content, :string, comment: 'Whoa, content describes itself!'
-      @connection.change_column :commenteds, :obvious, :string, comment: nil
-      @connection.add_index     :commenteds, :obvious, name: 'idx_obvious', comment: 'We need to see obvious comments'
-      # And check that these changes are reflected in dump
-      output = dump_table_schema 'commenteds'
-      assert_match %r[create_table "commenteds",.+\s+comment: "A table with comment"], output
-      assert_match %r[t\.string\s+"name",\s+comment: "Comment should help clarify the column purpose"], output
-      assert_match %r[t\.string\s+"obvious"\n], output
-      assert_match %r[t\.string\s+"content",\s+comment: "Whoa, content describes itself!"], output
-      assert_match %r[t\.integer\s+"rating",\s+comment: "I am running out of imagination"], output
-      assert_match %r[add_index\s+.+\s+comment: "\\\"Very important\\\" index that powers all the performance.\\nAnd it's fun!"], output
-      assert_match %r[add_index\s+.+\s+name: "idx_obvious",.+\s+comment: "We need to see obvious comments"], output
-    end
+  def test_schema_dump_with_comments
+    # Do all the stuff from other tests
+    @connection.add_column    :commenteds, :rating, :integer, comment: 'I am running out of imagination'
+    @connection.change_column :commenteds, :content, :string, comment: 'Whoa, content describes itself!'
+    @connection.change_column :commenteds, :obvious, :string, comment: nil
+    @connection.add_index     :commenteds, :obvious, name: 'idx_obvious', comment: 'We need to see obvious comments'
+
+    # And check that these changes are reflected in dump
+    output = dump_table_schema 'commenteds'
+    assert_match %r[create_table "commenteds",.+\s+comment: "A table with comment"], output
+    assert_match %r[t\.string\s+"name",\s+comment: "Comment should help clarify the column purpose"], output
+    assert_match %r[t\.string\s+"obvious"\n], output
+    assert_match %r[t\.string\s+"content",\s+comment: "Whoa, content describes itself!"], output
+    assert_match %r[t\.integer\s+"rating",\s+comment: "I am running out of imagination"], output
+    assert_match %r[add_index\s+.+\s+comment: "\\\"Very important\\\" index that powers all the performance.\\nAnd it's fun!"], output
+    assert_match %r[add_index\s+.+\s+name: "idx_obvious",.+\s+comment: "We need to see obvious comments"], output
+  end
+
+  def test_schema_dump_omits_blank_comments
+    output = dump_table_schema 'blank_comments'
+
+    assert_match %r[create_table "blank_comments"], output
+    assert_no_match %r[create_table "blank_comments",.+comment:], output
+
+    assert_match %r[t\.string\s+"space_comment"\n], output
+    assert_no_match %r[t\.string\s+"space_comment", comment:\n], output
+
+    assert_match %r[t\.string\s+"empty_comment"\n], output
+    assert_no_match %r[t\.string\s+"empty_comment", comment:\n], output
+
+    assert_match %r[t\.string\s+"nil_comment"\n], output
+    assert_no_match %r[t\.string\s+"nil_comment", comment:\n], output
+
+    assert_match %r[t\.string\s+"absent_comment"\n], output
+    assert_no_match %r[t\.string\s+"absent_comment", comment:\n], output
   end
 end
+
+end # if ActiveRecord::Base.connection.supports_comments?