Avoid noop update for Id only aggregates.

Closes #1309

Author: schauder

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/DefaultDataAccessStrategy.java

@@ -139,7 +139,12 @@ public <T> Object[] insert(List<InsertSubject<T>> insertSubjects, Class<T> domai
 	 */
 	@Override
 	public <S> boolean update(S instance, Class<S> domainType) {
-		return operations.update(sql(domainType).getUpdate(), sqlParametersFactory.forUpdate(instance, domainType)) != 0;
+
+		SqlIdentifierParameterSource parameterSource = sqlParametersFactory.forUpdate(instance, domainType);
+		if (parameterSource.size() <= 1) {
+			return true; // returning true, because conceptually the one row was correctly updated
+		}
+		return operations.update(sql(domainType).getUpdate(), parameterSource) != 0;
 	}
 
 	/*

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/SqlIdentifierParameterSource.java

@@ -81,4 +81,8 @@ void addAll(SqlIdentifierParameterSource others) {
 			addValue(identifier, others.getValue(name), others.getSqlType(name));
 		}
 	}
+
+	int size() {
+		return namesToValues.size();
+	}
 }

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/JdbcAggregateTemplateIntegrationTests.java

@@ -983,6 +983,16 @@ void insertWithIdOnly() {
 		assertThat(template.save(entity).id).isNotNull();
 	}
 
+	@Test // GH-1309
+	void updateIdOnlyAggregate() {
+
+		WithIdOnly entity = new WithIdOnly();
+
+		assertThat(template.save(entity).id).isNotNull();
+
+		template.save(entity);
+	}
+
 	@Test // GH-1232
 	@EnabledOnFeature(IS_HSQL)
 	void beforeSaveCallbackEffectsAreVisibleForInsert() {