DATAMONGO-2153 - Annotated aggregation support (sync).

The repository layer offers means interact with the aggregation framework via annotated repository finder methods. Similar to the JSON based queries a pipeline can be defined via the Aggregation annotation. The definition may contain simple placeholders like `?0` as well as SpEL expression markers `?#{ ... }`.

public interface PersonRepository extends CrudReppsitory<Person, String> {

  @Aggregation("{ $group: { _id : $lastname, names : { $addToSet : $?0 } } }")
  List<PersonAggregate> groupByLastnameAnd(String property);

  @Aggregation("{ $group: { _id : $lastname, names : { $addToSet : $firstname } } }")
  List<PersonAggregate> groupByLastnameAndFirstnames(Sort sort);

  @Aggregation("{ $group: { _id : $lastname, names : { $addToSet : $?0 } } }")
  List<PersonAggregate> groupByLastnameAnd(String property, Pageable page);

  @Aggregation("{ $group : { _id : null, total : { $sum : $age } } }")
  SumValue sumAgeUsingValueWrapper();

  @Aggregation("{ $group : { _id : null, total : { $sum : $age } } }")
  Long sumAge();

  @Aggregation("{ $group : { _id : null, total : { $sum : $age } } }")
  AggregationResults<SumValue> sumAgeRaw();
}

Author: christophstrobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AggregationOperationContext.java

@@ -17,6 +17,7 @@
 
 import org.bson.Document;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
+import org.springframework.lang.Nullable;
 
 /**
  * The context for an {@link AggregationOperation}.
@@ -33,7 +34,20 @@ public interface AggregationOperationContext {
 	 * @param document will never be {@literal null}.
 	 * @return must not be {@literal null}.
 	 */
-	Document getMappedObject(Document document);
+	default Document getMappedObject(Document document) {
+		return getMappedObject(document, null);
+	}
+
+	/**
+	 * Returns the mapped {@link Document}, potentially converting the source considering mapping metadata for the given
+	 * type.
+	 *
+	 * @param document will never be {@literal null}.
+	 * @param type can be {@literal null}.
+	 * @return must not be {@literal null}.
+	 * @since 2.2
+	 */
+	Document getMappedObject(Document document, @Nullable Class<?> type);
 
 	/**
 	 * Returns a {@link FieldReference} for the given field or {@literal null} if the context does not expose the given

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AggregationOperationRenderer.java

@@ -24,6 +24,7 @@
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
 import org.springframework.data.mongodb.core.aggregation.Fields.AggregationField;
 import org.springframework.data.mongodb.core.aggregation.FieldsExposingAggregationOperation.InheritsFieldsAggregationOperation;
+import org.springframework.lang.Nullable;
 
 /**
  * Rendering support for {@link AggregationOperation} into a {@link List} of {@link org.bson.Document}.
@@ -75,15 +76,16 @@ static List<Document> toDocument(List<AggregationOperation> operations, Aggregat
 	 * Simple {@link AggregationOperationContext} that just returns {@link FieldReference}s as is.
 	 *
 	 * @author Oliver Gierke
+	 * @author Christoph Strobl
 	 */
 	private static class NoOpAggregationOperationContext implements AggregationOperationContext {
 
 		/*
 		 * (non-Javadoc)
-		 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document)
+		 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document, java.lang.Class)
 		 */
 		@Override
-		public Document getMappedObject(Document document) {
+		public Document getMappedObject(Document document, @Nullable Class<?> type) {
 			return document;
 		}
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ExposedFieldsAggregationOperationContext.java

@@ -56,11 +56,11 @@ public ExposedFieldsAggregationOperationContext(ExposedFields exposedFields,
 
 	/*
 	 * (non-Javadoc)
-	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document, java.lang.Class)
 	 */
 	@Override
-	public Document getMappedObject(Document document) {
-		return rootContext.getMappedObject(document);
+	public Document getMappedObject(Document document, @Nullable Class<?> type) {
+		return rootContext.getMappedObject(document, type);
 	}
 
 	/*

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/NestedDelegatingExpressionAggregationOperationContext.java

@@ -45,11 +45,11 @@ public NestedDelegatingExpressionAggregationOperationContext(AggregationOperatio
 
 	/*
 	 * (non-Javadoc)
-	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document, java.lang.Class)
 	 */
 	@Override
-	public Document getMappedObject(Document document) {
-		return delegate.getMappedObject(document);
+	public Document getMappedObject(Document document, Class<?> type) {
+		return delegate.getMappedObject(document, type);
 	}
 
 	/*

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/PrefixingDelegatingAggregationOperationContext.java

@@ -25,6 +25,7 @@
 
 import org.bson.Document;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
+import org.springframework.lang.Nullable;
 
 /**
  * {@link AggregationOperationContext} implementation prefixing non-command keys on root level with the given prefix.
@@ -56,11 +57,11 @@ public PrefixingDelegatingAggregationOperationContext(AggregationOperationContex
 
 	/*
 	 * (non-Javadoc)
-	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document, java.lang.Class)
 	 */
 	@Override
-	public Document getMappedObject(Document document) {
-		return doPrefix(delegate.getMappedObject(document));
+	public Document getMappedObject(Document document, @Nullable Class<?> type) {
+		return doPrefix(delegate.getMappedObject(document, type));
 	}
 
 	/*

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/TypeBasedAggregationOperationContext.java

@@ -27,6 +27,7 @@
 import org.springframework.data.mongodb.core.convert.QueryMapper;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -70,7 +71,16 @@ public TypeBasedAggregationOperationContext(Class<?> type,
 	 */
 	@Override
 	public Document getMappedObject(Document document) {
-		return mapper.getMappedObject(document, mappingContext.getPersistentEntity(type));
+		return getMappedObject(document, type);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document, java.lang.Class)
+	 */
+	@Override
+	public Document getMappedObject(Document document, @Nullable Class<?> type) {
+		return mapper.getMappedObject(document, type != null ? mappingContext.getPersistentEntity(type) : null);
 	}
 
 	/*

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

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.repository;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.core.annotation.AliasFor;
+import org.springframework.data.annotation.QueryAnnotation;
+
+/**
+ * NOTE for self: <br />
+ * - Creates a typed aggregation using the repository type as input type and the method return type as target. <br />
+ * - Collation still needs to be done. <br />
+ *
+ * @author Christoph Strobl
+ * @since 2.2
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.METHOD, ElementType.ANNOTATION_TYPE })
+@Documented
+@QueryAnnotation
+public @interface Aggregation {
+
+	@AliasFor("pipeline")
+	String[] value() default {};
+
+	@AliasFor("value")
+	String[] pipeline() default {};
+
+	// TODO: add collation support once merged
+}

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

@@ -80,23 +80,28 @@ public MongoQueryMethod getQueryMethod() {
 	@Override
 	public Object execute(Object[] parameters) {
 
-		ConvertingParameterAccessor accessor = new ConvertingParameterAccessor(operations.getConverter(),
+ 		ConvertingParameterAccessor accessor = new ConvertingParameterAccessor(operations.getConverter(),
 				new MongoParametersParameterAccessor(method, parameters));
+
+		ResultProcessor processor = method.getResultProcessor().withDynamicProjection(accessor);
+		Class<?> typeToRead = processor.getReturnedType().getTypeToRead();
+
+		return processor.processResult(doExecute(method, accessor, typeToRead));
+	}
+
+	protected Object doExecute(MongoQueryMethod method, ConvertingParameterAccessor accessor, Class<?> typeToRead) {
+
 		Query query = createQuery(accessor);
 
 		applyQueryMetaAttributesWhenPresent(query);
 		query = applyAnnotatedDefaultSortIfPresent(query);
 
-		ResultProcessor processor = method.getResultProcessor().withDynamicProjection(accessor);
-		Class<?> typeToRead = processor.getReturnedType().getTypeToRead();
-
 		FindWithQuery<?> find = typeToRead == null //
 				? executableFind //
 				: executableFind.as(typeToRead);
 
 		MongoQueryExecution execution = getExecution(accessor, find);
-
-		return processor.processResult(execution.execute(query));
+		return execution.execute(query);
 	}
 
 	private MongoQueryExecution getExecution(ConvertingParameterAccessor accessor, FindWithQuery<?> operation) {
@@ -204,4 +209,5 @@ protected Query createCountQuery(ConvertingParameterAccessor accessor) {
 	 * @since 2.0.4
 	 */
 	protected abstract boolean isLimiting();
+
 }

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

@@ -30,6 +30,7 @@
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
+import org.springframework.data.mongodb.repository.Aggregation;
 import org.springframework.data.mongodb.repository.Meta;
 import org.springframework.data.mongodb.repository.Query;
 import org.springframework.data.mongodb.repository.Tailable;
@@ -167,6 +168,15 @@ public MongoEntityMetadata<?> getEntityInformation() {
 		return this.metadata;
 	}
 
+	/**
+	 *
+	 * @return
+	 * @since 2.2
+	 */
+	Class<?> repositoryDomainType() {
+		return getDomainClass();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.repository.query.QueryMethod#getParameters()
@@ -322,6 +332,39 @@ public String getAnnotatedSort() {
 				"Expected to find @Query annotation but did not. Make sure to check hasAnnotatedSort() before."));
 	}
 
+	/**
+	 * Returns whether the method has an annotated query.
+	 *
+	 * @return
+	 * @since 2.2
+	 */
+	public boolean hasAnnotatedAggregation() {
+		return findAnnotatedAggregation().isPresent();
+	}
+
+	/**
+	 * Returns the query string declared in a {@link Query} annotation or {@literal null} if neither the annotation found
+	 * nor the attribute was specified.
+	 *
+	 * @return
+	 * @since 2.2
+	 */
+	@Nullable
+	public String[] getAnnotatedAggregation() {
+		return findAnnotatedAggregation().orElse(null);
+	}
+
+	private Optional<String[]> findAnnotatedAggregation() {
+
+		return lookupAggregationAnnotation() //
+				.map(Aggregation::pipeline) //
+				.filter(it -> !ObjectUtils.isEmpty(it));
+	}
+
+	Optional<Aggregation> lookupAggregationAnnotation() {
+		return doFindAnnotation(Aggregation.class);
+	}
+
 	@SuppressWarnings("unchecked")
 	private <A extends Annotation> Optional<A> doFindAnnotation(Class<A> annotationType) {