#523 - Add example for declarative MongoDB aggregations.

Original pull request: #526.
closes: #523

mongodb/aggregation/README.md

@@ -0,0 +1,53 @@
+# Spring Data MongoDB - Aggregations
+
+This project contains usage samples for using MongoDB [Aggregations](https://docs.mongodb.com/manual/aggregation/) 
+showing both the programmatic and declarative approach for integrating an Aggregation Pipeline into the repository lay.
+
+## Programmatic
+
+The programmatic approach uses a [custom repository](https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#repositories.custom-implementations) implementation along with the [Aggregation Framework](https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#mongo.aggregation).
+
+```java
+class OrderRepositoryImpl implements OrderRepositoryCustom {
+
+	private MongoOperations operations;
+	
+	// ...
+
+	@Override
+	public Invoice getInvoiceFor(Order order) {
+
+		AggregationResults<Invoice> results = operations.aggregate(newAggregation(Order.class, 
+			match(where("id").is(order.getId())), 
+			unwind("items"), 
+			project("id", "customerId", "items") 
+				.andExpression("'$items.price' * '$items.quantity'").as("lineTotal"), 
+			group("id") 
+				.sum("lineTotal").as("netAmount") 
+				.addToSet("items").as("items"), 
+			project("id", "items", "netAmount") 
+				.and("orderId").previousOperation() 
+				.andExpression("netAmount * [0]", taxRate).as("taxAmount") 
+				.andExpression("netAmount * (1 + [0])", taxRate).as("totalAmount") 
+		), Invoice.class);
+
+		return results.getUniqueMappedResult();
+	}
+}
+```
+
+## Declarative
+
+The [declarative approach](https://docs.spring.io/spring-data/mongodb/docs/2.2.0.RC2/reference/html/#mongodb.repositories.queries.aggregation) allows to define an Aggregation Pipeline via the `@Aggregation` annotation.
+
+```java
+public interface OrderRepository extends CrudRepository<Order, String>, OrderRepositoryCustom {
+
+	@Aggregation("{ $group : { _id : $customerId, total : { $sum : 1 } } }")
+	List<OrdersPerCustomer> totalOrdersPerCustomer(Sort sort);
+
+	@Aggregation(pipeline = { "{ $match : { customerId : ?0 } }", "{ $count : total }" })
+	Long totalOrdersForCustomer(String customerId);
+}
+```
+

mongodb/aggregation/src/main/java/example/springdata/mongodb/aggregation/OrderRepository.java

@@ -15,6 +15,10 @@
  */
 package example.springdata.mongodb.aggregation;
 
+import java.util.List;
+
+import org.springframework.data.domain.Sort;
+import org.springframework.data.mongodb.repository.Aggregation;
 import org.springframework.data.repository.CrudRepository;
 
 /**
@@ -22,7 +26,13 @@ import org.springframework.data.repository.CrudRepository;
  *
  * @author Thomas Darimont
  * @author Oliver Gierke
+ * @author Christoph Strobl
  */
 public interface OrderRepository extends CrudRepository<Order, String>, OrderRepositoryCustom {
 
+	@Aggregation("{ $group : { _id : $customerId, total : { $sum : 1 } } }")
+	List<OrdersPerCustomer> totalOrdersPerCustomer(Sort sort);
+
+	@Aggregation(pipeline = { "{ $match : { customerId : ?0 } }", "{ $count : total }" })
+	Long totalOrdersForCustomer(String customerId);
 }

mongodb/aggregation/src/main/java/example/springdata/mongodb/aggregation/OrdersPerCustomer.java

@@ -0,0 +1,31 @@
+/*
+ * 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 example.springdata.mongodb.aggregation;
+
+import lombok.Value;
+
+import org.springframework.data.annotation.Id;
+
+/**
+ * @author Christoph Strobl
+ */
+@Value
+public class OrdersPerCustomer {
+
+	@Id //
+	private String customerId;
+	private Long total;
+}

mongodb/aggregation/src/test/java/example/springdata/mongodb/aggregation/OrderRepositoryIntegrationTests.java

@@ -21,11 +21,13 @@ import static org.junit.Assert.*;
 
 import java.util.Date;
 
+import org.assertj.core.api.Assertions;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.data.domain.Sort;
 import org.springframework.test.context.junit4.SpringRunner;
 
 /**
@@ -33,6 +35,7 @@ import org.springframework.test.context.junit4.SpringRunner;
  *
  * @author Thomas Darimont
  * @author Oliver Gierke
+ * @author Christoph Strobl
  */
 @RunWith(SpringRunner.class)
 @SpringBootTest
@@ -64,4 +67,33 @@ public class OrderRepositoryIntegrationTests {
 		assertThat(invoice.getTaxAmount(), is(closeTo(1.577, 000001)));
 		assertThat(invoice.getTotalAmount(), is(closeTo(9.877, 000001)));
 	}
+
+	@Test
+	public void declarativeAggregationWithSort() {
+
+		repository.save(new Order("c42", new Date()).addItem(product1));
+		repository.save(new Order("c42", new Date()).addItem(product2));
+		repository.save(new Order("c42", new Date()).addItem(product3));
+
+		repository.save(new Order("b12", new Date()).addItem(product1));
+		repository.save(new Order("b12", new Date()).addItem(product1));
+
+		Assertions.assertThat(repository.totalOrdersPerCustomer(Sort.by(Sort.Order.desc("total")))) //
+				.containsExactly( //
+						new OrdersPerCustomer("c42", 3L), new OrdersPerCustomer("b12", 2L) //
+				);
+	}
+
+	@Test
+	public void multiStageDeclarativeAggregation() {
+
+		repository.save(new Order("c42", new Date()).addItem(product1));
+		repository.save(new Order("c42", new Date()).addItem(product2));
+		repository.save(new Order("c42", new Date()).addItem(product3));
+
+		repository.save(new Order("b12", new Date()).addItem(product1));
+		repository.save(new Order("b12", new Date()).addItem(product1));
+
+		Assertions.assertThat(repository.totalOrdersForCustomer("c42")).isEqualTo(3);
+	}
 }