Fix query mapping resolution of properties using underscore within field name.

Closes: #3601
Original pull request: #3607.

Author: christophstrobl

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

@@ -1170,7 +1170,7 @@ private PersistentPropertyPath<MongoPersistentProperty> getPath(String pathExpre
 
 			if (sourceProperty != null && sourceProperty.getOwner().equals(entity)) {
 				return mappingContext
-						.getPersistentPropertyPath(PropertyPath.from(sourceProperty.getName(), entity.getTypeInformation()));
+						.getPersistentPropertyPath(PropertyPath.from(Pattern.quote(sourceProperty.getName()), entity.getTypeInformation()));
 			}
 
 			PropertyPath path = forName(rawPath);
@@ -1229,6 +1229,13 @@ private PropertyPath forName(String path) {
 					return forName(path.substring(0, path.length() - 3) + "id");
 				}
 
+				// Ok give it another try quoting
+				try {
+					return PropertyPath.from(Pattern.quote(path), entity.getTypeInformation());
+				} catch (PropertyReferenceException | InvalidPersistentPropertyPath ex) {
+
+				}
+
 				return null;
 			}
 		}

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

@@ -1191,6 +1191,72 @@ void projectOnUnwrappedValue() {
 		assertThat(document).isEqualTo(new org.bson.Document("stringValue", 1));
 	}
 
+	@Test // GH-3601
+	void resolvesFieldnameWithUnderscoresCorrectly() {
+
+		Query query = query(where("fieldname_with_underscores").exists(true));
+
+		org.bson.Document document = mapper.getMappedObject(query.getQueryObject(),
+				context.getPersistentEntity(WithPropertyUsingUnderscoreInName.class));
+
+		assertThat(document).isEqualTo(new org.bson.Document("fieldname_with_underscores", new org.bson.Document("$exists", true)));
+	}
+
+	@Test // GH-3601
+	void resolvesMappedFieldnameWithUnderscoresCorrectly() {
+
+		Query query = query(where("renamed_fieldname_with_underscores").exists(true));
+
+		org.bson.Document document = mapper.getMappedObject(query.getQueryObject(),
+				context.getPersistentEntity(WithPropertyUsingUnderscoreInName.class));
+
+		assertThat(document).isEqualTo(new org.bson.Document("renamed", new org.bson.Document("$exists", true)));
+	}
+
+	@Test // GH-3601
+	void resolvesSimpleNestedFieldnameWithUnderscoresCorrectly() {
+
+		Query query = query(where("simple.fieldname_with_underscores").exists(true));
+
+		org.bson.Document document = mapper.getMappedObject(query.getQueryObject(),
+				context.getPersistentEntity(WrapperAroundWithPropertyUsingUnderscoreInName.class));
+
+		assertThat(document).isEqualTo(new org.bson.Document("simple.fieldname_with_underscores", new org.bson.Document("$exists", true)));
+	}
+
+	@Test // GH-3601
+	void resolvesSimpleNestedMappedFieldnameWithUnderscoresCorrectly() {
+
+		Query query = query(where("simple.renamed_fieldname_with_underscores").exists(true));
+
+		org.bson.Document document = mapper.getMappedObject(query.getQueryObject(),
+				context.getPersistentEntity(WrapperAroundWithPropertyUsingUnderscoreInName.class));
+
+		assertThat(document).isEqualTo(new org.bson.Document("simple.renamed", new org.bson.Document("$exists", true)));
+	}
+
+	@Test // GH-3601
+	void resolvesFieldNameWithUnderscoreOnNestedFieldnameWithUnderscoresCorrectly() {
+
+		Query query = query(where("double_underscore.fieldname_with_underscores").exists(true));
+
+		org.bson.Document document = mapper.getMappedObject(query.getQueryObject(),
+				context.getPersistentEntity(WrapperAroundWithPropertyUsingUnderscoreInName.class));
+
+		assertThat(document).isEqualTo(new org.bson.Document("double_underscore.fieldname_with_underscores", new org.bson.Document("$exists", true)));
+	}
+
+	@Test // GH-3601
+	void resolvesFieldNameWithUnderscoreOnNestedMappedFieldnameWithUnderscoresCorrectly() {
+
+		Query query = query(where("double_underscore.renamed_fieldname_with_underscores").exists(true));
+
+		org.bson.Document document = mapper.getMappedObject(query.getQueryObject(),
+				context.getPersistentEntity(WrapperAroundWithPropertyUsingUnderscoreInName.class));
+
+		assertThat(document).isEqualTo(new org.bson.Document("double_underscore.renamed", new org.bson.Document("$exists", true)));
+	}
+
 	class WithDeepArrayNesting {
 
 		List<WithNestedArray> level0;
@@ -1408,4 +1474,17 @@ static class UnwrappableType {
 		String transientValue;
 	}
 
+	static class WrapperAroundWithPropertyUsingUnderscoreInName {
+
+		WithPropertyUsingUnderscoreInName simple;
+		WithPropertyUsingUnderscoreInName double_underscore;
+	}
+
+	static class WithPropertyUsingUnderscoreInName {
+
+		String fieldname_with_underscores;
+
+		@Field("renamed")
+		String renamed_fieldname_with_underscores;
+	}
 }