Refactor String-based repository aggretation methods into common utility callback.

Also, support aggregation result projections for reactive flows.

See #4839
Original pull request: #4841

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

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.repository.query;
 
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
+import reactor.util.function.Tuple2;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -61,7 +62,6 @@ import org.springframework.data.repository.query.RepositoryQuery;
 import org.springframework.data.repository.query.ResultProcessor;
 import org.springframework.data.repository.query.ValueExpressionDelegate;
 import org.springframework.data.spel.ExpressionDependencies;
-import org.springframework.data.util.TypeInformation;
 import org.springframework.expression.ExpressionParser;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.lang.Nullable;
@@ -70,7 +70,6 @@ import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 
 import com.mongodb.MongoClientSettings;
-import reactor.util.function.Tuple2;
 
 /**
  * Base class for reactive {@link RepositoryQuery} implementations for MongoDB.
@@ -112,16 +111,20 @@ public abstract class AbstractReactiveMongoQuery implements RepositoryQuery {
 		this.method = method;
 		this.operations = operations;
 		this.instantiators = new EntityInstantiators();
-		this.valueExpressionDelegate = new ValueExpressionDelegate(new QueryMethodValueEvaluationContextAccessor(new StandardEnvironment(), evaluationContextProvider.getEvaluationContextProvider()), ValueExpressionParser.create(() -> expressionParser));
+		this.valueExpressionDelegate = new ValueExpressionDelegate(
+				new QueryMethodValueEvaluationContextAccessor(new StandardEnvironment(),
+						evaluationContextProvider.getEvaluationContextProvider()),
+				ValueExpressionParser.create(() -> expressionParser));
 
 		MongoEntityMetadata<?> metadata = method.getEntityInformation();
 		Class<?> type = metadata.getCollectionEntity().getType();
 
 		this.findOperationWithProjection = operations.query(type);
 		this.updateOps = operations.update(type);
-		ValueEvaluationContextProvider valueContextProvider = valueExpressionDelegate.createValueContextProvider(
-				method.getParameters());
-		Assert.isInstanceOf(ReactiveValueEvaluationContextProvider.class, valueContextProvider, "ValueEvaluationContextProvider must be reactive");
+		ValueEvaluationContextProvider valueContextProvider = valueExpressionDelegate
+				.createValueContextProvider(method.getParameters());
+		Assert.isInstanceOf(ReactiveValueEvaluationContextProvider.class, valueContextProvider,
+				"ValueEvaluationContextProvider must be reactive");
 		this.valueEvaluationContextProvider = (ReactiveValueEvaluationContextProvider) valueContextProvider;
 	}
 
@@ -151,9 +154,10 @@ public abstract class AbstractReactiveMongoQuery implements RepositoryQuery {
 
 		this.findOperationWithProjection = operations.query(type);
 		this.updateOps = operations.update(type);
-		ValueEvaluationContextProvider valueContextProvider = valueExpressionDelegate.createValueContextProvider(
-				method.getParameters());
-		Assert.isInstanceOf(ReactiveValueEvaluationContextProvider.class, valueContextProvider, "ValueEvaluationContextProvider must be reactive");
+		ValueEvaluationContextProvider valueContextProvider = valueExpressionDelegate
+				.createValueContextProvider(method.getParameters());
+		Assert.isInstanceOf(ReactiveValueEvaluationContextProvider.class, valueContextProvider,
+				"ValueEvaluationContextProvider must be reactive");
 		this.valueEvaluationContextProvider = (ReactiveValueEvaluationContextProvider) valueContextProvider;
 	}
 
@@ -182,14 +186,9 @@ public abstract class AbstractReactiveMongoQuery implements RepositoryQuery {
 		ConvertingParameterAccessor accessor = new ConvertingParameterAccessor(operations.getConverter(),
 				parameterAccessor);
 
-		TypeInformation<?> returnType = method.getReturnType();
 		ResultProcessor processor = method.getResultProcessor().withDynamicProjection(accessor);
 		Class<?> typeToRead = processor.getReturnedType().getTypeToRead();
 
-		if (typeToRead == null && returnType.getComponentType() != null) {
-			typeToRead = returnType.getComponentType().getType();
-		}
-
 		return doExecute(method, processor, accessor, typeToRead);
 	}
 
@@ -221,11 +220,15 @@ public abstract class AbstractReactiveMongoQuery implements RepositoryQuery {
 			String collection = method.getEntityInformation().getCollectionName();
 
 			ReactiveMongoQueryExecution execution = getExecution(accessor,
-					new ResultProcessingConverter(processor, operations, instantiators), find);
+					getResultProcessing(processor), find);
 			return execution.execute(query, processor.getReturnedType().getDomainType(), collection);
 		});
 	}
 
+	ResultProcessingConverter getResultProcessing(ResultProcessor processor) {
+		return new ResultProcessingConverter(processor, operations, instantiators);
+	}
+
 	/**
 	 * Returns the execution instance to use.
 	 *
@@ -439,8 +442,8 @@ public abstract class AbstractReactiveMongoQuery implements RepositoryQuery {
 		return getValueExpressionEvaluatorLater(dependencies, accessor).zipWith(Mono.just(codec));
 	}
 
-	private Document decode(Tuple2<ValueExpressionEvaluator, ParameterBindingDocumentCodec> expressionEvaluator, String source, MongoParameterAccessor accessor,
-			ParameterBindingDocumentCodec codec) {
+	private Document decode(Tuple2<ValueExpressionEvaluator, ParameterBindingDocumentCodec> expressionEvaluator,
+			String source, MongoParameterAccessor accessor, ParameterBindingDocumentCodec codec) {
 
 		ParameterBindingContext bindingContext = new ParameterBindingContext(accessor::getBindableValue,
 				expressionEvaluator.getT1());
@@ -490,8 +493,8 @@ public abstract class AbstractReactiveMongoQuery implements RepositoryQuery {
 			@Override
 			public <T> T evaluate(String expressionString) {
 				ValueExpression expression = valueExpressionDelegate.parse(expressionString);
-				ValueEvaluationContext evaluationContext = valueEvaluationContextProvider.getEvaluationContext(accessor.getValues(),
-						expression.getExpressionDependencies());
+				ValueEvaluationContext evaluationContext = valueEvaluationContextProvider
+						.getEvaluationContext(accessor.getValues(), expression.getExpressionDependencies());
 				return (T) expression.evaluate(evaluationContext);
 			}
 		};
@@ -509,8 +512,9 @@ public abstract class AbstractReactiveMongoQuery implements RepositoryQuery {
 	protected Mono<ValueExpressionEvaluator> getValueExpressionEvaluatorLater(ExpressionDependencies dependencies,
 			MongoParameterAccessor accessor) {
 
-			return valueEvaluationContextProvider.getEvaluationContextLater(accessor.getValues(), dependencies)
-					.map(evaluationContext -> new ValueExpressionDelegateValueExpressionEvaluator(valueExpressionDelegate, valueExpression -> evaluationContext));
+		return valueEvaluationContextProvider.getEvaluationContextLater(accessor.getValues(), dependencies)
+				.map(evaluationContext -> new ValueExpressionDelegateValueExpressionEvaluator(valueExpressionDelegate,
+						valueExpression -> evaluationContext));
 	}
 
 	/**

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

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.repository.query;
 
 import java.time.Duration;
 import java.util.Map;
+import java.util.function.Function;
 import java.util.function.IntUnaryOperator;
 import java.util.function.LongUnaryOperator;
 
@@ -28,11 +29,18 @@ import org.springframework.data.mapping.model.ValueExpressionEvaluator;
 import org.springframework.data.mongodb.core.aggregation.Aggregation;
 import org.springframework.data.mongodb.core.aggregation.AggregationOptions;
 import org.springframework.data.mongodb.core.aggregation.AggregationPipeline;
+import org.springframework.data.mongodb.core.aggregation.AggregationResults;
+import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
 import org.springframework.data.mongodb.core.mapping.FieldName;
+import org.springframework.data.mongodb.core.mapping.MongoSimpleTypes;
 import org.springframework.data.mongodb.core.query.Collation;
 import org.springframework.data.mongodb.core.query.Meta;
 import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.data.repository.query.ResultProcessor;
+import org.springframework.data.repository.query.ReturnedType;
+import org.springframework.data.util.ReflectionUtils;
+import org.springframework.data.util.TypeInformation;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
@@ -116,13 +124,15 @@ abstract class AggregationUtils {
 	}
 
 	/**
-	 * If present apply the preference from the {@link org.springframework.data.mongodb.repository.ReadPreference} annotation.
+	 * If present apply the preference from the {@link org.springframework.data.mongodb.repository.ReadPreference}
+	 * annotation.
 	 *
 	 * @param builder must not be {@literal null}.
 	 * @return never {@literal null}.
 	 * @since 4.2
 	 */
-	static AggregationOptions.Builder applyReadPreference(AggregationOptions.Builder builder, MongoQueryMethod queryMethod) {
+	static AggregationOptions.Builder applyReadPreference(AggregationOptions.Builder builder,
+			MongoQueryMethod queryMethod) {
 
 		if (!queryMethod.hasAnnotatedReadPreference()) {
 			return builder;
@@ -131,6 +141,93 @@ abstract class AggregationUtils {
 		return builder.readPreference(ReadPreference.valueOf(queryMethod.getAnnotatedReadPreference()));
 	}
 
+	static AggregationOptions computeOptions(MongoQueryMethod method, ConvertingParameterAccessor accessor,
+			AggregationPipeline pipeline, ValueExpressionEvaluator evaluator) {
+
+		AggregationOptions.Builder builder = Aggregation.newAggregationOptions();
+
+		AggregationUtils.applyCollation(builder, method.getAnnotatedCollation(), accessor, evaluator);
+		AggregationUtils.applyMeta(builder, method);
+		AggregationUtils.applyHint(builder, method);
+		AggregationUtils.applyReadPreference(builder, method);
+
+		TypeInformation<?> returnType = method.getReturnType();
+		if (returnType.getComponentType() != null) {
+			returnType = returnType.getRequiredComponentType();
+		}
+		if (ReflectionUtils.isVoid(returnType.getType()) && pipeline.isOutOrMerge()) {
+			builder.skipOutput();
+		}
+
+		return builder.build();
+	}
+
+	/**
+	 * Prepares the AggregationPipeline including type discovery and calling {@link AggregationCallback} to run the
+	 * aggregation.
+	 */
+	@Nullable
+	static <T> T doAggregate(AggregationPipeline pipeline, MongoQueryMethod method, ResultProcessor processor,
+			ConvertingParameterAccessor accessor,
+			Function<MongoParameterAccessor, ValueExpressionEvaluator> evaluatorFunction, AggregationCallback<T> callback) {
+
+		Class<?> sourceType = method.getDomainClass();
+		ReturnedType returnedType = processor.getReturnedType();
+		// 🙈Interface Projections do not happen on the Aggregation level but through our repository infrastructure.
+		// Non-projections and raw results (AggregationResults<…>) are handled here. Interface projections read a Document
+		// and DTO projections read the returned type.
+		// We also support simple return types (String) that are read from a Document
+		TypeInformation<?> returnType = method.getReturnType();
+		Class<?> returnElementType = (returnType.getComponentType() != null ? returnType.getRequiredComponentType()
+				: returnType).getType();
+		Class<?> entityType;
+
+		boolean isRawAggregationResult = ClassUtils.isAssignable(AggregationResults.class, method.getReturnedObjectType());
+
+		if (returnElementType.equals(Document.class)) {
+			entityType = sourceType;
+		} else {
+			entityType = returnElementType;
+		}
+
+		AggregationUtils.appendSortIfPresent(pipeline, accessor, entityType);
+
+		if (method.isSliceQuery()) {
+			AggregationUtils.appendLimitAndOffsetIfPresent(pipeline, accessor, LongUnaryOperator.identity(),
+					limit -> limit + 1);
+		} else {
+			AggregationUtils.appendLimitAndOffsetIfPresent(pipeline, accessor);
+		}
+
+		AggregationOptions options = AggregationUtils.computeOptions(method, accessor, pipeline,
+				evaluatorFunction.apply(accessor));
+		TypedAggregation<?> aggregation = new TypedAggregation<>(sourceType, pipeline.getOperations(), options);
+
+		boolean isSimpleReturnType = MongoSimpleTypes.HOLDER.isSimpleType(returnElementType);
+		Class<?> typeToRead;
+
+		if (isSimpleReturnType) {
+			typeToRead = Document.class;
+		} else if (isRawAggregationResult) {
+			typeToRead = returnElementType;
+		} else {
+
+			if (returnedType.isProjecting()) {
+				typeToRead = returnedType.getReturnedType().isInterface() ? Document.class : returnedType.getReturnedType();
+			} else {
+				typeToRead = entityType;
+			}
+		}
+
+		return callback.doAggregate(aggregation, sourceType, typeToRead, returnElementType, isSimpleReturnType,
+				isRawAggregationResult);
+	}
+
+	static AggregationPipeline computePipeline(AbstractMongoQuery mongoQuery, MongoQueryMethod method,
+			ConvertingParameterAccessor accessor) {
+		return new AggregationPipeline(mongoQuery.parseAggregationPipeline(method.getAnnotatedAggregation(), accessor));
+	}
+
 	/**
 	 * Append {@code $sort} aggregation stage if {@link ConvertingParameterAccessor#getSort()} is present.
 	 *
@@ -139,7 +236,7 @@ abstract class AggregationUtils {
 	 * @param targetType
 	 */
 	static void appendSortIfPresent(AggregationPipeline aggregationPipeline, ConvertingParameterAccessor accessor,
-			Class<?> targetType) {
+			@Nullable Class<?> targetType) {
 
 		if (accessor.getSort().isUnsorted()) {
 			return;
@@ -254,4 +351,26 @@ abstract class AggregationUtils {
 
 		return converter.getConversionService().convert(value, targetType);
 	}
+
+	/**
+	 * Interface to invoke an aggregation along with source, intermediate, and target types.
+	 *
+	 * @param <T>
+	 */
+	interface AggregationCallback<T> {
+
+		/**
+		 * @param aggregation
+		 * @param domainType
+		 * @param typeToRead
+		 * @param elementType
+		 * @param simpleType whether the aggregation returns {@link Document} or a
+		 *          {@link org.springframework.data.mapping.model.SimpleTypeHolder simple type}.
+		 * @param rawResult whether the aggregation returns {@link AggregationResults}.
+		 * @return
+		 */
+		@Nullable
+		T doAggregate(TypedAggregation<?> aggregation, Class<?> domainType, Class<?> typeToRead, Class<?> elementType,
+				boolean simpleType, boolean rawResult);
+	}
 }

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

@@ -24,11 +24,8 @@ import org.bson.Document;
 import org.reactivestreams.Publisher;
 
 import org.springframework.data.mongodb.core.ReactiveMongoOperations;
-import org.springframework.data.mongodb.core.aggregation.Aggregation;
 import org.springframework.data.mongodb.core.aggregation.AggregationOperation;
-import org.springframework.data.mongodb.core.aggregation.AggregationOptions;
 import org.springframework.data.mongodb.core.aggregation.AggregationPipeline;
-import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
 import org.springframework.data.mongodb.core.mapping.MongoSimpleTypes;
 import org.springframework.data.mongodb.core.query.Query;
@@ -36,9 +33,8 @@ import org.springframework.data.repository.query.ReactiveQueryMethodEvaluationCo
 import org.springframework.data.repository.query.ResultProcessor;
 import org.springframework.data.repository.query.ValueExpressionDelegate;
 import org.springframework.data.util.ReflectionUtils;
-import org.springframework.data.util.TypeInformation;
 import org.springframework.expression.ExpressionParser;
-import org.springframework.util.ClassUtils;
+import org.springframework.lang.Nullable;
 
 /**
  * A reactive {@link org.springframework.data.repository.query.RepositoryQuery} to use a plain JSON String to create an
@@ -87,46 +83,39 @@ public class ReactiveStringBasedAggregation extends AbstractReactiveMongoQuery {
 	}
 
 	@Override
+	@SuppressWarnings("ReactiveStreamsNullableInLambdaInTransform")
 	protected Publisher<Object> doExecute(ReactiveMongoQueryMethod method, ResultProcessor processor,
-			ConvertingParameterAccessor accessor, Class<?> typeToRead) {
+			ConvertingParameterAccessor accessor, @Nullable Class<?> ignored) {
 
 		return computePipeline(accessor).flatMapMany(it -> {
 
-			Class<?> sourceType = method.getDomainClass();
-			Class<?> targetType = typeToRead;
+			return AggregationUtils.doAggregate(new AggregationPipeline(it), method, processor, accessor,
+					this::getValueExpressionEvaluator,
+					(aggregation, sourceType, typeToRead, elementType, simpleType, rawResult) -> {
 
-			AggregationPipeline pipeline = new AggregationPipeline(it);
+						Flux<?> flux = reactiveMongoOperations.aggregate(aggregation, typeToRead);
+						if (ReflectionUtils.isVoid(elementType)) {
+							return flux.then();
+						}
 
-			AggregationUtils.appendSortIfPresent(pipeline, accessor, typeToRead);
-			AggregationUtils.appendLimitAndOffsetIfPresent(pipeline, accessor);
+						ReactiveMongoQueryExecution.ResultProcessingConverter resultProcessing = getResultProcessing(processor);
 
-			boolean isSimpleReturnType = isSimpleReturnType(typeToRead);
-			boolean isRawReturnType = ClassUtils.isAssignable(org.bson.Document.class, typeToRead);
+						if (simpleType && !rawResult && !elementType.equals(Document.class)) {
 
-			if (isSimpleReturnType || isRawReturnType) {
-				targetType = Document.class;
-			}
+							flux = flux.handle((item, sink) -> {
 
-			AggregationOptions options = computeOptions(method, accessor, pipeline);
-			TypedAggregation<?> aggregation = new TypedAggregation<>(sourceType, pipeline.getOperations(), options);
+								Object result = AggregationUtils.extractSimpleTypeResult((Document) item, elementType, mongoConverter);
 
-			Flux<?> flux = reactiveMongoOperations.aggregate(aggregation, targetType);
-			if (ReflectionUtils.isVoid(typeToRead)) {
-				return flux.then();
-			}
+								if (result != null) {
+									sink.next(result);
+								}
+							});
+						}
 
-			if (isSimpleReturnType && !isRawReturnType) {
-				flux = flux.handle((item, sink) -> {
+						flux = flux.map(resultProcessing::convert);
 
-					Object result = AggregationUtils.extractSimpleTypeResult((Document) item, typeToRead, mongoConverter);
-
-					if (result != null) {
-						sink.next(result);
-					}
-				});
-			}
-
-			return method.isCollectionQuery() ? flux : flux.next();
+						return method.isCollectionQuery() ? flux : flux.next();
+					});
 		});
 	}
 
@@ -138,28 +127,6 @@ public class ReactiveStringBasedAggregation extends AbstractReactiveMongoQuery {
 		return parseAggregationPipeline(getQueryMethod().getAnnotatedAggregation(), accessor);
 	}
 
-	private AggregationOptions computeOptions(MongoQueryMethod method, ConvertingParameterAccessor accessor,
-			AggregationPipeline pipeline) {
-
-		AggregationOptions.Builder builder = Aggregation.newAggregationOptions();
-
-		AggregationUtils.applyCollation(builder, method.getAnnotatedCollation(), accessor,
-				getValueExpressionEvaluator(accessor));
-		AggregationUtils.applyMeta(builder, method);
-		AggregationUtils.applyHint(builder, method);
-		AggregationUtils.applyReadPreference(builder, method);
-
-		TypeInformation<?> returnType = method.getReturnType();
-		if (returnType.getComponentType() != null) {
-			returnType = returnType.getRequiredComponentType();
-		}
-		if (ReflectionUtils.isVoid(returnType.getType()) && pipeline.isOutOrMerge()) {
-			builder.skipOutput();
-		}
-
-		return builder.build();
-	}
-
 	@Override
 	protected Mono<Query> createQuery(ConvertingParameterAccessor accessor) {
 		throw new UnsupportedOperationException("No query support for aggregation");

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

@@ -17,7 +17,6 @@ package org.springframework.data.mongodb.repository.query;
 
 import java.util.ArrayList;
 import java.util.List;
-import java.util.function.LongUnaryOperator;
 import java.util.stream.Stream;
 
 import org.bson.Document;
@@ -26,11 +25,7 @@ import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.SliceImpl;
 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.AggregationOptions;
-import org.springframework.data.mongodb.core.aggregation.AggregationPipeline;
 import org.springframework.data.mongodb.core.aggregation.AggregationResults;
-import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
 import org.springframework.data.mongodb.core.mapping.MongoSimpleTypes;
 import org.springframework.data.mongodb.core.query.Query;
@@ -41,7 +36,6 @@ import org.springframework.data.repository.query.ValueExpressionDelegate;
 import org.springframework.data.util.ReflectionUtils;
 import org.springframework.expression.ExpressionParser;
 import org.springframework.lang.Nullable;
-import org.springframework.util.ClassUtils;
 
 /**
  * {@link AbstractMongoQuery} implementation to run string-based aggregations using
@@ -103,87 +97,67 @@ public class StringBasedAggregation extends AbstractMongoQuery {
 		this.mongoConverter = mongoOperations.getConverter();
 	}
 
+	@SuppressWarnings("unchecked")
 	@Override
 	@Nullable
-	protected Object doExecute(MongoQueryMethod method, ResultProcessor resultProcessor,
-			ConvertingParameterAccessor accessor, @Nullable Class<?> typeToRead) {
+	protected Object doExecute(MongoQueryMethod method, ResultProcessor processor, ConvertingParameterAccessor accessor,
+			@Nullable Class<?> ignore) {
 
-		Class<?> sourceType = method.getDomainClass();
-		Class<?> targetType = typeToRead;
+		return AggregationUtils.doAggregate(AggregationUtils.computePipeline(this, method, accessor), method, processor,
+				accessor, this::getExpressionEvaluatorFor,
+				(aggregation, sourceType, typeToRead, elementType, simpleType, rawResult) -> {
 
-		AggregationPipeline pipeline = computePipeline(method, accessor);
-		AggregationUtils.appendSortIfPresent(pipeline, accessor, typeToRead);
+					if (method.isStreamQuery()) {
 
-		if (method.isSliceQuery()) {
-			AggregationUtils.appendLimitAndOffsetIfPresent(pipeline, accessor, LongUnaryOperator.identity(),
-					limit -> limit + 1);
-		} else {
-			AggregationUtils.appendLimitAndOffsetIfPresent(pipeline, accessor);
-		}
+						Stream<?> stream = mongoOperations.aggregateStream(aggregation, typeToRead);
 
-		boolean isSimpleReturnType = typeToRead != null && isSimpleReturnType(typeToRead);
-		boolean isRawAggregationResult = typeToRead != null && ClassUtils.isAssignable(AggregationResults.class, typeToRead);
+						if (!simpleType || elementType.equals(Document.class)) {
+							return stream;
+						}
 
-		if (isSimpleReturnType) {
-			targetType = Document.class;
-		} else if (isRawAggregationResult) {
+						return stream
+								.map(it -> AggregationUtils.extractSimpleTypeResult((Document) it, elementType, mongoConverter));
+					}
 
-			// 🙈
-			targetType = method.getReturnType().getRequiredActualType().getRequiredComponentType().getType();
-		} else if (resultProcessor.getReturnedType().isProjecting()) {
-			targetType = resultProcessor.getReturnedType().getReturnedType().isInterface() ? Document.class :resultProcessor.getReturnedType().getReturnedType();
-		}
+					AggregationResults<Object> result = (AggregationResults<Object>) mongoOperations.aggregate(aggregation,
+							typeToRead);
 
-		AggregationOptions options = computeOptions(method, accessor, pipeline);
-		TypedAggregation<?> aggregation = new TypedAggregation<>(sourceType, pipeline.getOperations(), options);
+					if (ReflectionUtils.isVoid(elementType)) {
+						return null;
+					}
 
-		if (method.isStreamQuery()) {
+					if (rawResult) {
+						return result;
+					}
 
-			Stream<?> stream = mongoOperations.aggregateStream(aggregation, targetType);
+					List<?> results = result.getMappedResults();
+					if (method.isCollectionQuery()) {
+						return simpleType ? convertResults(elementType, (List<Document>) results) : results;
+					}
 
-			if (isSimpleReturnType) {
-				return stream.map(it -> AggregationUtils.extractSimpleTypeResult((Document) it, typeToRead, mongoConverter));
-			}
+					if (method.isSliceQuery()) {
 
-			return stream;
-		}
+						Pageable pageable = accessor.getPageable();
+						int pageSize = pageable.getPageSize();
+						List<Object> resultsToUse = simpleType ? convertResults(elementType, (List<Document>) results)
+								: (List<Object>) results;
+						boolean hasNext = resultsToUse.size() > pageSize;
+						return new SliceImpl<>(hasNext ? resultsToUse.subList(0, pageSize) : resultsToUse, pageable, hasNext);
+					}
 
-		AggregationResults<Object> result = (AggregationResults<Object>) mongoOperations.aggregate(aggregation, targetType);
-		if (typeToRead != null && ReflectionUtils.isVoid(typeToRead)) {
-			return null;
-		}
+					Object uniqueResult = result.getUniqueMappedResult();
 
-		if (isRawAggregationResult) {
-			return result;
-		}
-
-		List<Object> results = result.getMappedResults();
-		if (method.isCollectionQuery()) {
-			return isSimpleReturnType ? convertResults(typeToRead, results) : results;
-		}
-
-		if (method.isSliceQuery()) {
-
-			Pageable pageable = accessor.getPageable();
-			int pageSize = pageable.getPageSize();
-			List<Object> resultsToUse = isSimpleReturnType ? convertResults(typeToRead, results) : results;
-			boolean hasNext = resultsToUse.size() > pageSize;
-			return new SliceImpl<>(hasNext ? resultsToUse.subList(0, pageSize) : resultsToUse, pageable, hasNext);
-		}
-
-		Object uniqueResult = result.getUniqueMappedResult();
-
-		return isSimpleReturnType
-				? AggregationUtils.extractSimpleTypeResult((Document) uniqueResult, typeToRead, mongoConverter)
-				: uniqueResult;
+					return simpleType
+							? AggregationUtils.extractSimpleTypeResult((Document) uniqueResult, elementType, mongoConverter)
+							: uniqueResult;
+				});
 	}
 
-	private List<Object> convertResults(Class<?> typeToRead, List<Object> mappedResults) {
+	private List<Object> convertResults(Class<?> targetType, List<Document> mappedResults) {
 
 		List<Object> list = new ArrayList<>(mappedResults.size());
-		for (Object it : mappedResults) {
-			Object extractSimpleTypeResult = AggregationUtils.extractSimpleTypeResult((Document) it, typeToRead,
-					mongoConverter);
+		for (Document it : mappedResults) {
+			Object extractSimpleTypeResult = AggregationUtils.extractSimpleTypeResult(it, targetType, mongoConverter);
 			list.add(extractSimpleTypeResult);
 		}
 		return list;
@@ -193,28 +167,6 @@ public class StringBasedAggregation extends AbstractMongoQuery {
 		return MongoSimpleTypes.HOLDER.isSimpleType(targetType);
 	}
 
-	AggregationPipeline computePipeline(MongoQueryMethod method, ConvertingParameterAccessor accessor) {
-		return new AggregationPipeline(parseAggregationPipeline(method.getAnnotatedAggregation(), accessor));
-	}
-
-	private AggregationOptions computeOptions(MongoQueryMethod method, ConvertingParameterAccessor accessor,
-			AggregationPipeline pipeline) {
-
-		AggregationOptions.Builder builder = Aggregation.newAggregationOptions();
-
-		AggregationUtils.applyCollation(builder, method.getAnnotatedCollation(), accessor,
-				getExpressionEvaluatorFor(accessor));
-		AggregationUtils.applyMeta(builder, method);
-		AggregationUtils.applyHint(builder, method);
-		AggregationUtils.applyReadPreference(builder, method);
-
-		if (ReflectionUtils.isVoid(method.getReturnType().getType()) && pipeline.isOutOrMerge()) {
-			builder.skipOutput();
-		}
-
-		return builder.build();
-	}
-
 	@Override
 	protected Query createQuery(ConvertingParameterAccessor accessor) {
 		throw new UnsupportedOperationException("No query support for aggregation");

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

@@ -1396,6 +1396,18 @@ public abstract class AbstractPersonRepositoryIntegrationTests implements Dirtie
 		}
 	}
 
+	@Test // DATAMONGO-4841
+	void annotatedAggregationStreamWithPlaceholderValue() {
+
+		assertThat(repository.groupStreamByLastnameAnd("firstname"))
+				.contains(new PersonAggregate("Lessard", Collections.singletonList("Stefan"))) //
+				.contains(new PersonAggregate("Keys", Collections.singletonList("Alicia"))) //
+				.contains(new PersonAggregate("Tinsley", Collections.singletonList("Boyd"))) //
+				.contains(new PersonAggregate("Beauford", Collections.singletonList("Carter"))) //
+				.contains(new PersonAggregate("Moore", Collections.singletonList("Leroi"))) //
+				.contains(new PersonAggregate("Matthews", Arrays.asList("Dave", "Oliver August")));
+	}
+
 	@Test // DATAMONGO-2153
 	void annotatedAggregationWithPlaceholderValue() {
 

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

@@ -27,10 +27,10 @@ import org.springframework.data.domain.Limit;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.Range;
-import org.springframework.data.domain.Window;
 import org.springframework.data.domain.ScrollPosition;
 import org.springframework.data.domain.Slice;
 import org.springframework.data.domain.Sort;
+import org.springframework.data.domain.Window;
 import org.springframework.data.geo.Box;
 import org.springframework.data.geo.Circle;
 import org.springframework.data.geo.Distance;
@@ -413,6 +413,9 @@ public interface PersonRepository extends MongoRepository<Person, String>, Query
 	@Aggregation("{ '$project': { '_id' : '$lastname' } }")
 	Stream<String> findAllLastnamesAsStream();
 
+	@Aggregation("{ '$group': { '_id' : '$lastname', names : { $addToSet : '$?0' } } }")
+	Stream<PersonAggregate> groupStreamByLastnameAnd(String property);
+
 	@Aggregation("{ '$group': { '_id' : '$lastname', names : { $addToSet : '$?0' } } }")
 	List<PersonAggregate> groupByLastnameAnd(String property);
 

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

@@ -600,6 +600,17 @@ class ReactiveMongoRepositoryTests implements DirtiesStateExtension.StateFunctio
 				}).verifyComplete();
 	}
 
+	@Test // GH-4839
+	void annotatedAggregationWithAggregationResultAsClosedInterfaceProjection() {
+
+		repository.findAggregatedClosedInterfaceProjectionBy() //
+				.as(StepVerifier::create) //
+				.consumeNextWith(it -> {
+					assertThat(it.getFirstname()).isIn(dave.getFirstname(), oliver.getFirstname());
+					assertThat(it.getLastname()).isEqualTo(dave.getLastname());
+				}).expectNextCount(1).verifyComplete();
+	}
+
 	@Test // DATAMONGO-2403
 	@DirtiesState
 	void annotatedAggregationExtractingSimpleValueIsEmptyForEmptyDocument() {
@@ -816,6 +827,10 @@ class ReactiveMongoRepositoryTests implements DirtiesStateExtension.StateFunctio
 		@Aggregation(pipeline = "{ '$group' : { '_id' : null, 'total' : { $sum: '$age' } } }")
 		Mono<Map> sumAgeAndReturnSumAsMap();
 
+		@Aggregation({ "{ '$match' :  { 'lastname' :  'Matthews'} }",
+				"{ '$project': { _id : 0, firstname : 1, lastname : 1 } }" })
+		Flux<PersonSummary> findAggregatedClosedInterfaceProjectionBy();
+
 		@Aggregation(
 				pipeline = { "{ '$match' : { 'firstname' : '?0' } }", "{ '$project' : { '_id' : 0, 'lastname' : 1 } }" })
 		Mono<String> projectToLastnameAndRemoveId(String firstname);

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

@@ -32,4 +32,5 @@ public interface ReactivePersonRepository extends ReactiveMongoRepository<Person
 	 * @return
 	 */
 	Flux<Person> findByLastname(String lastname);
+
 }