DATAMONGO-1471 - Converter only applies identifier values if actually available.

Setting the value for the identifier property is an explicit step in MappingMongoConverter and always executed if the type to be created has an identifier property. If the source document doesn't contain an _id field (e.g. because it has been excluded explicitly) that previously caused null to be set on the identifier. This caused an exception if the identifier property is a primitive type.

We now explicitly check whether the field backing the identifier property is actually present in the source document and only explicitly set the value if so.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/DBObjectAccessor.java

@@ -114,6 +114,40 @@ class DBObjectAccessor {
 		return result;
 	}
 
+	/**
+	 * Returns whether the underlying {@link DBObject} has a value ({@literal null} or non-{@literal null}) for the given
+	 * {@link MongoPersistentProperty}.
+	 * 
+	 * @param property must not be {@literal null}.
+	 * @return
+	 */
+	public boolean hasValue(MongoPersistentProperty property) {
+
+		Assert.notNull(property, "Property must not be null!");
+
+		String fieldName = property.getFieldName();
+
+		if (!fieldName.contains(".")) {
+			return this.dbObject.containsField(fieldName);
+		}
+
+		String[] parts = fieldName.split("\\.");
+		Map<String, Object> source = this.dbObject;
+		Object result = null;
+
+		for (int i = 1; i < parts.length; i++) {
+
+			result = source.get(parts[i - 1]);
+			source = getAsMap(result);
+
+			if (source == null) {
+				return false;
+			}
+		}
+
+		return source.containsKey(parts[parts.length - 1]);
+	}
+
 	/**
 	 * Returns the given source object as map, i.e. {@link BasicDBObject}s and maps as is or {@literal null} otherwise.
 	 * 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java

@@ -260,7 +260,7 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 		// make sure id property is set before all other properties
 		Object idValue = null;
 
-		if (idProperty != null) {
+		if (idProperty != null && new DBObjectAccessor(dbo).hasValue(idProperty)) {
 			idValue = getValueInternal(idProperty, dbo, evaluator, path);
 			accessor.setProperty(idProperty, idValue);
 		}

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/DBObjectAccessorUnitTests.java

@@ -101,6 +101,20 @@ public class DBObjectAccessorUnitTests {
 		assertThat(nestedA.get("c"), is((Object) "c"));
 	}
 
+	/**
+	 * @see DATAMONGO-1471
+	 */
+	@Test
+	public void exposesAvailabilityOfFields() {
+
+		DBObjectAccessor accessor = new DBObjectAccessor(new BasicDBObject("a", new BasicDBObject("c", "d")));
+		MongoPersistentEntity<?> entity = context.getPersistentEntity(ProjectingType.class);
+
+		assertThat(accessor.hasValue(entity.getPersistentProperty("foo")), is(false));
+		assertThat(accessor.hasValue(entity.getPersistentProperty("a")), is(true));
+		assertThat(accessor.hasValue(entity.getPersistentProperty("name")), is(false));
+	}
+
 	static class ProjectingType {
 
 		String name;

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -2066,6 +2066,14 @@ public class MappingMongoConverterUnitTests {
 		assertThat(target.map.get(FooBarEnum.FOO), is("spring"));
 	}
 
+	/**
+	 * @see DATAMONGO-1471
+	 */
+	@Test
+	public void readsDocumentWithPrimitiveIdButNoValue() {
+		assertThat(converter.read(ClassWithIntId.class, new BasicDBObject()), is(notNullValue()));
+	}
+
 	static class GenericType<T> {
 		T content;
 	}