DATACMNS-1199 - Added PropertyPath.nested(…).

This allows to obtain a nested property path based on a currently available one.

Author: odrotbohm

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

@@ -195,6 +195,21 @@ public boolean isCollection() {
 		return isCollection;
 	}
 
+	/**
+	 * Returns the {@link PropertyPath} for the path nested under the current property.
+	 *
+	 * @param path must not be {@literal null} or empty.
+	 * @return will never be {@literal null}.
+	 */
+	public PropertyPath nested(String path) {
+
+		Assert.hasText(path, "Path must not be null or empty!");
+
+		String lookup = toDotPath().concat(".").concat(path);
+
+		return PropertyPath.from(lookup, owningType);
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Iterable#iterator()

src/test/java/org/springframework/data/mapping/PropertyPathUnitTests.java

@@ -355,6 +355,20 @@ public void exposesLeafPropertyType() {
 		assertThat(from("user.name", Bar.class).getLeafType()).isEqualTo(String.class);
 	}
 
+	@Test // DATACMNS-1199
+	public void createsNestedPropertyPath() {
+		assertThat(from("user", Bar.class).nested("name")).isEqualTo(from("user.name", Bar.class));
+	}
+
+	@Test // DATACMNS-1199
+	public void rejectsNonExistantNestedPath() {
+
+		assertThatExceptionOfType(PropertyReferenceException.class) //
+				.isThrownBy(() -> from("user", Bar.class).nested("nonexistant")) //
+				.withMessageContaining("nonexistant") //
+				.withMessageContaining("Bar.user");
+	}
+
 	private class Foo {
 
 		String userName;