DATAMONGO-2506 - Provide meaningful error message when using unsupported return type in repository aggregation method.

We improved the error message for unsupported return types instead of running into an IllegalArgumentException for unique results.

Original pull request: spring-projects#851.

Author: christophstrobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/StringBasedAggregation.java

@@ -20,6 +20,7 @@
 
 import org.bson.Document;
 
+import org.springframework.data.mongodb.InvalidMongoDbApiUsageException;
 import org.springframework.data.mongodb.core.MongoOperations;
 import org.springframework.data.mongodb.core.aggregation.Aggregation;
 import org.springframework.data.mongodb.core.aggregation.AggregationOperation;
@@ -71,6 +72,10 @@ public StringBasedAggregation(MongoQueryMethod method, MongoOperations mongoOper
 	protected Object doExecute(MongoQueryMethod method, ResultProcessor resultProcessor,
 			ConvertingParameterAccessor accessor, Class<?> typeToRead) {
 
+		if (method.isPageQuery() || method.isSliceQuery()) {
+			throw new InvalidMongoDbApiUsageException(String.format("Repository aggregation method '%s' does not support '%s' return type. Please use eg. 'List' instead.", method.getName(), method.getReturnType().getType().getSimpleName()));
+		}
+
 		Class<?> sourceType = method.getDomainClass();
 		Class<?> targetType = typeToRead;
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/query/StringBasedAggregationUnitTests.java

@@ -34,9 +34,14 @@
 import org.mockito.ArgumentCaptor;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
-
+import org.mockito.junit.jupiter.MockitoSettings;
+import org.mockito.quality.Strictness;
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.domain.Sort.Direction;
+import org.springframework.data.mongodb.InvalidMongoDbApiUsageException;
 import org.springframework.data.mongodb.core.MongoOperations;
 import org.springframework.data.mongodb.core.aggregation.AggregationOperationContext;
 import org.springframework.data.mongodb.core.aggregation.AggregationOptions;
@@ -68,6 +73,7 @@
  * @author Mark Paluch
  */
 @ExtendWith(MockitoExtension.class)
+@MockitoSettings(strictness = Strictness.LENIENT)
 public class StringBasedAggregationUnitTests {
 
 	SpelExpressionParser PARSER = new SpelExpressionParser();
@@ -202,6 +208,16 @@ public void aggregateWithCollationParameter() {
 		assertThat(collationOf(invocation)).isEqualTo(Collation.of("en_US"));
 	}
 
+	@Test // DATAMONGO-2506
+	public void aggregateRaisesErrorOnInvalidReturnType() {
+
+		StringBasedAggregation sba = createAggregationForMethod("invalidPageReturnType", Pageable.class);
+		assertThatExceptionOfType(InvalidMongoDbApiUsageException.class) //
+				.isThrownBy(() -> sba.execute(new Object[] { PageRequest.of(0, 1) })) //
+				.withMessageContaining("invalidPageReturnType") //
+				.withMessageContaining("Page");
+	}
+
 	private AggregationInvocation executeAggregation(String name, Object... args) {
 
 		Class<?>[] argTypes = Arrays.stream(args).map(Object::getClass).toArray(Class[]::new);
@@ -280,6 +296,9 @@ private interface SampleRepository extends Repository<Person, Long> {
 
 		@Aggregation(pipeline = RAW_GROUP_BY_LASTNAME_STRING, collation = "de_AT")
 		PersonAggregate aggregateWithCollation(Collation collation);
+
+		@Aggregation(RAW_GROUP_BY_LASTNAME_STRING)
+		Page<Person> invalidPageReturnType(Pageable page);
 	}
 
 	static class PersonAggregate {