Add ability to remove value from enum type

README.md

@@ -56,6 +56,14 @@ To add a value into existing enum:
 add_enum_value :mood, "pensive"
 ```
 
+To remove a value from existing enum:
+
+> :warning: Make sure that value is not used anywhere in the database.
+
+```ruby
+remove_enum_value :mood, "pensive"
+```
+
 To add a new enum column to an existing table:
 
 ```ruby

lib/active_record/postgres_enum/postgresql_adapter.rb

@@ -65,6 +65,15 @@ def add_enum_value(name, value, after: nil, before: nil)
         execute sql
       end
 
+      def remove_enum_value(name, value)
+        sql = %{
+          DELETE FROM pg_enum
+          WHERE enumlabel=#{quote value}
+          AND enumtypid=(SELECT oid FROM pg_type WHERE typname='#{name}')
+        }
+        execute sql
+      end
+
       def rename_enum_value(name, existing_value, new_value)
         raise "Renaming enum values is only supported in PostgreSQL 10.0+" unless rename_enum_value_supported?
 

spec/active_record/postgres_enum_spec.rb

@@ -65,6 +65,35 @@
       expect(connection.enums[:foo]).to eq ["a1", "a2", 'a"3']
     end
 
+    it "removes an enum value" do
+      expect { connection.remove_enum_value(:foo, "a1") }.to_not raise_error
+      expect(connection.enums[:foo]).to eq %w(a2)
+    end
+
+    it "removes an enum value with a space" do
+      expect { connection.add_enum_value(:foo, "a 3") }.to_not raise_error
+      expect { connection.remove_enum_value(:foo, "a 3") }.to_not raise_error
+      expect(connection.enums[:foo]).to eq %w(a1 a2)
+    end
+
+    it "removes an enum value with a comma" do
+      expect { connection.add_enum_value(:foo, "a,3") }.to_not raise_error
+      expect { connection.remove_enum_value(:foo, "a,3") }.to_not raise_error
+      expect(connection.enums[:foo]).to eq %w(a1 a2)
+    end
+
+    it "removes an enum value with a single quote" do
+      expect { connection.add_enum_value(:foo, "a'3") }.to_not raise_error
+      expect { connection.remove_enum_value(:foo, "a'3") }.to_not raise_error
+      expect(connection.enums[:foo]).to eq %w(a1 a2)
+    end
+
+    it "removes an enum value with a double quote" do
+      expect { connection.add_enum_value(:foo, "a\"3") }.to_not raise_error
+      expect { connection.remove_enum_value(:foo, "a\"3") }.to_not raise_error
+      expect(connection.enums[:foo]).to eq %w(a1 a2)
+    end
+
     it "renames an enum value" do
       expect { connection.rename_enum_value(:foo, "a2", "b2") }.to_not raise_error
       expect(connection.enums[:foo]).to eq %w(a1 b2)