DATACMNS-1322 - Added @Immutable to allow users to express a persistent entity to be considered immutable.

This is needed for downstream projects that attempt to merge persistent entity instances and previously didn't have a chance to detect that an object had to be set as-is instead of being merged recursively.

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

@@ -18,6 +18,7 @@ package org.springframework.data.mapping;
 import java.lang.annotation.Annotation;
 import java.util.Iterator;
 
+import org.springframework.data.annotation.Immutable;
 import org.springframework.data.convert.EntityInstantiator;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.lang.Nullable;
@@ -305,4 +306,14 @@ public interface PersistentEntity<T, P extends PersistentProperty<P>> extends It
 	 * @return whether the given bean is considered a new instance.
 	 */
 	boolean isNew(Object bean);
+
+	/**
+	 * Returns whether the entity is considered immutable, i.e. clients shouldn't attempt to change instances via the
+	 * {@link PersistentPropertyAccessor} obtained via {@link #getPropertyAccessor(Object)}.
+	 * 
+	 * @return
+	 * @see Immutable
+	 * @since 2.1
+	 */
+	boolean isImmutable();
 }

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

@@ -33,6 +33,7 @@ import java.util.TreeSet;
 import java.util.stream.Collectors;
 
 import org.springframework.core.annotation.AnnotatedElementUtils;
+import org.springframework.data.annotation.Immutable;
 import org.springframework.data.annotation.TypeAlias;
 import org.springframework.data.domain.Persistable;
 import org.springframework.data.mapping.Alias;
@@ -93,6 +94,7 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 
 	private final Lazy<Alias> typeAlias;
 	private final Lazy<IsNewStrategy> isNewStrategy;
+	private final Lazy<Boolean> isImmutable;
 
 	/**
 	 * Creates a new {@link BasicPersistentEntity} from the given {@link TypeInformation}.
@@ -130,7 +132,7 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 		this.isNewStrategy = Lazy.of(() -> Persistable.class.isAssignableFrom(information.getType()) //
 				? PersistableIsNewStrategy.INSTANCE
 				: PersistentEntityIsNewStrategy.of(this));
-
+		this.isImmutable = Lazy.of(() -> isAnnotationPresent(Immutable.class));
 	}
 
 	/*
@@ -496,6 +498,15 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 		return isNewStrategy.get().isNew(bean);
 	}
 
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mapping.PersistentEntity#isImmutable()
+	 */
+	@Override
+	public boolean isImmutable() {
+		return isImmutable.get();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Iterable#iterator()