Add a converter for CurrencyUnits stored in the database (#334)

* Add a converter for CurrencyUnits stored in the database

This uses the well-known String representation for currency units. It also
provides a base class for other converters that will be persisting the
toString() representation.

* Add DB and formatting changes

* Add tests, make minor fixes

core/src/main/java/google/registry/persistence/CurrencyUnitConverter.java

@@ -0,0 +1,29 @@
+// Copyright 2019 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package google.registry.persistence;
+
+import javax.annotation.Nullable;
+import javax.persistence.Converter;
+import org.joda.money.CurrencyUnit;
+
+/** JPA converter for {@link CurrencyUnit}s. */
+@Converter(autoApply = true)
+public class CurrencyUnitConverter extends ToStringConverterBase<CurrencyUnit> {
+
+  @Override
+  @Nullable
+  public CurrencyUnit convertToEntityAttribute(@Nullable String columnValue) {
+    return (columnValue == null) ? null : CurrencyUnit.of(columnValue);
+  }
+}

core/src/main/java/google/registry/persistence/ToStringConverterBase.java

@@ -0,0 +1,27 @@
+// Copyright 2019 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package google.registry.persistence;
+
+import javax.annotation.Nullable;
+import javax.persistence.AttributeConverter;
+
+/** Abstract JPA converter for objects that are stored by their toString() value. */
+abstract class ToStringConverterBase<T> implements AttributeConverter<T, String> {
+
+  @Override
+  @Nullable
+  public String convertToDatabaseColumn(@Nullable T entity) {
+    return (entity == null) ? null : entity.toString();
+  }
+}

core/src/main/resources/META-INF/persistence.xml

@@ -35,6 +35,7 @@
     <!-- Customized type converters -->
     <class>google.registry.persistence.BloomFilterConverter</class>
     <class>google.registry.persistence.CreateAutoTimestampConverter</class>
+    <class>google.registry.persistence.CurrencyUnitConverter</class>
     <class>google.registry.persistence.UpdateAutoTimestampConverter</class>
     <class>google.registry.persistence.ZonedDateTimeConverter</class>