DATACMNS-1366 - Introduce PersistentEntity.requiresPropertyPopulation().

The newly introduced method indicates whether any properties have to be populated to create instances of the entity. This is useful for objects that are completely initialized through their constructors as converters then can avoid iterating over all properties just to find out none of them have to be populated.

Author: odrotbohm

src/main/java/org/springframework/data/mapping/PersistentEntity.java

@@ -316,4 +316,13 @@ default <A extends Annotation> A getRequiredAnnotation(Class<A> annotationType)
 	 * @since 2.1
 	 */
 	boolean isImmutable();
+
+	/**
+	 * Returns whether the entity needs properties to be populated, i.e. if any property exists that's not initialized by
+	 * the constructor.
+	 * 
+	 * @return
+	 * @since 2.1
+	 */
+	boolean requiresPropertyPopulation();
 }

src/main/java/org/springframework/data/mapping/model/BasicPersistentEntity.java

@@ -95,6 +95,7 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 	private final Lazy<Alias> typeAlias;
 	private final Lazy<IsNewStrategy> isNewStrategy;
 	private final Lazy<Boolean> isImmutable;
+	private final Lazy<Boolean> requiresPropertyPopulation;
 
 	/**
 	 * Creates a new {@link BasicPersistentEntity} from the given {@link TypeInformation}.
@@ -134,6 +135,8 @@ public BasicPersistentEntity(TypeInformation<T> information, @Nullable Comparato
 				: getFallbackIsNewStrategy());
 
 		this.isImmutable = Lazy.of(() -> isAnnotationPresent(Immutable.class));
+		this.requiresPropertyPopulation = Lazy.of(() -> !isImmutable() && properties.stream() //
+				.anyMatch(it -> !(isConstructorArgument(it) || it.isTransient())));
 	}
 
 	/*
@@ -508,6 +511,15 @@ public boolean isImmutable() {
 		return isImmutable.get();
 	}
 
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mapping.PersistentEntity#requiresPropertyPopulation()
+	 */
+	@Override
+	public boolean requiresPropertyPopulation() {
+		return requiresPropertyPopulation.get();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Iterable#iterator()

src/test/java/org/springframework/data/mapping/model/BasicPersistentEntityUnitTests.java

@@ -19,6 +19,8 @@
 import static org.junit.Assume.*;
 import static org.mockito.Mockito.*;
 
+import lombok.RequiredArgsConstructor;
+
 import java.lang.annotation.Annotation;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -27,6 +29,7 @@
 import java.util.List;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.stream.Stream;
 
 import org.hamcrest.CoreMatchers;
 import org.junit.Rule;
@@ -44,6 +47,7 @@
 import org.springframework.data.annotation.Immutable;
 import org.springframework.data.annotation.LastModifiedBy;
 import org.springframework.data.annotation.Persistent;
+import org.springframework.data.annotation.Transient;
 import org.springframework.data.annotation.TypeAlias;
 import org.springframework.data.domain.Persistable;
 import org.springframework.data.mapping.Alias;
@@ -355,6 +359,19 @@ public void detectsImmutableEntity() {
 		assertThat(createEntity(Entity.class).isImmutable()).isFalse();
 	}
 
+	@Test // DATACMNS-1366
+	public void exposesPropertyPopulationRequired() {
+
+		assertThat(createPopulatedPersistentEntity(PropertyPopulationRequired.class).requiresPropertyPopulation()).isTrue();
+	}
+
+	@Test // DATACMNS-1366
+	public void exposesPropertyPopulationNotRequired() {
+
+		Stream.of(PropertyPopulationNotRequired.class, PropertyPopulationNotRequiredWithTransient.class) //
+				.forEach(it -> assertThat(createPopulatedPersistentEntity(it).requiresPropertyPopulation()).isFalse());
+	}
+
 	private <S> BasicPersistentEntity<S, T> createEntity(Class<S> type) {
 		return createEntity(type, null);
 	}
@@ -363,6 +380,12 @@ private <S> BasicPersistentEntity<S, T> createEntity(Class<S> type, Comparator<T
 		return new BasicPersistentEntity<>(ClassTypeInformation.from(type), comparator);
 	}
 
+	private static PersistentEntity<Object, ?> createPopulatedPersistentEntity(Class<?> type) {
+
+		SampleMappingContext context = new SampleMappingContext();
+		return context.getRequiredPersistentEntity(type);
+	}
+
 	@TypeAlias("foo")
 	static class AliasedEntity {
 
@@ -427,4 +450,26 @@ public boolean isNew() {
 
 	@Immutable
 	static class SomeValue {}
+
+	// DATACMNS-1366
+
+	@RequiredArgsConstructor
+	static class PropertyPopulationRequired {
+
+		private final String firstname, lastname;
+		private String email;
+	}
+
+	@RequiredArgsConstructor
+	static class PropertyPopulationNotRequired {
+
+		private final String firstname, lastname;
+	}
+
+	@RequiredArgsConstructor
+	static class PropertyPopulationNotRequiredWithTransient {
+
+		private final String firstname, lastname;
+		private @Transient String email;
+	}
 }