DATAMONGO-840 - Improve support for nested field references in SpEL expressions within Projections.

We now correctly add a compound expression that represents a field reference to the previous operation arguments if necessary.

Original pull request: #118.

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2014 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.
@@ -495,7 +495,7 @@ class SpelExpressionTransformer implements AggregationExpressionTransformer {
 
 			if (currentNode.hasfirstChildNotOfType(Indexer.class)) {
 				// we have a property path expression like: foo.bar -> render as reference
-				return context.getFieldReference().toString();
+				return context.addToPreviousOrReturn(context.getFieldReference().toString());
 			}
 
 			return context.addToPreviousOrReturn(currentNode.getValue());

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/AggregationTests.java

@@ -782,6 +782,46 @@ public class AggregationTests {
 		assertThat(String.valueOf(firstItem.get("_id")), is("u1"));
 	}
 
+	/**
+	 * @see DATAMONGO-840
+	 */
+	@Test
+	public void shouldAggregateOrderDataToAnInvoice() {
+
+		mongoTemplate.dropCollection(Order.class);
+
+		double taxRate = 0.19;
+
+		LineItem product1 = new LineItem("1", "p1", 1.23);
+		LineItem product2 = new LineItem("2", "p2", 0.87, 2);
+		LineItem product3 = new LineItem("3", "p3", 5.33);
+
+		Order order = new Order("o4711", "c42", new Date()).addItem(product1).addItem(product2).addItem(product3);
+
+		mongoTemplate.save(order);
+
+		AggregationResults<Invoice> results = mongoTemplate.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);
+
+		Invoice invoice = results.getUniqueMappedResult();
+
+		assertThat(invoice, is(notNullValue()));
+		assertThat(invoice.getOrderId(), is(order.getId()));
+		assertThat(invoice.getNetAmount(), is(closeTo(8.3, 000001)));
+		assertThat(invoice.getTaxAmount(), is(closeTo(1.577, 000001)));
+		assertThat(invoice.getTotalAmount(), is(closeTo(9.877, 000001)));
+	}
+
 	private void assertLikeStats(LikeStats like, String id, long count) {
 
 		assertThat(like, is(notNullValue()));

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/Invoice.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2014 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
+ *
+ *      http://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.core.aggregation;
+
+import java.util.List;
+
+/**
+ * @author Thomas Darimont
+ */
+public class Invoice {
+
+	String orderId;
+
+	double taxAmount;
+
+	double netAmount;
+
+	double totalAmount;
+
+	List<LineItem> items;
+
+	public String getOrderId() {
+		return orderId;
+	}
+
+	public void setOrderId(String orderId) {
+		this.orderId = orderId;
+	}
+
+	public double getTaxAmount() {
+		return taxAmount;
+	}
+
+	public void setTaxAmount(double taxAmount) {
+		this.taxAmount = taxAmount;
+	}
+
+	public double getNetAmount() {
+		return netAmount;
+	}
+
+	public void setNetAmount(double netAmount) {
+		this.netAmount = netAmount;
+	}
+
+	public double getTotalAmount() {
+		return totalAmount;
+	}
+
+	public void setTotalAmount(double totalAmount) {
+		this.totalAmount = totalAmount;
+	}
+
+	public List<LineItem> getItems() {
+		return items;
+	}
+
+	public void setItems(List<LineItem> items) {
+		this.items = items;
+	}
+}

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/LineItem.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2014 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
+ *
+ *      http://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.core.aggregation;
+
+/**
+ * @author Thomas Darimont
+ */
+public class LineItem {
+
+	final String id;
+
+	final String caption;
+
+	final double price;
+
+	int quantity = 1;
+
+	@SuppressWarnings("unused")
+	private LineItem() {
+		this(null, null, 0.0, 0);
+	}
+
+	public LineItem(String id, String caption, double price) {
+		this.id = id;
+		this.caption = caption;
+		this.price = price;
+	}
+
+	public LineItem(String id, String caption, double price, int quantity) {
+		this(id, caption, price);
+		this.quantity = quantity;
+	}
+}

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/Order.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2014 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
+ *
+ *      http://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.core.aggregation;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Date;
+import java.util.List;
+
+/**
+ * @author Thomas Darimont
+ */
+public class Order {
+
+	final String id;
+
+	final String customerId;
+
+	final Date orderDate;
+
+	final List<LineItem> items;
+
+	public Order(String id, String customerId, Date orderDate) {
+		this(id, customerId, orderDate, new ArrayList<LineItem>());
+	}
+
+	public Order(String id, String customerId, Date orderDate, List<LineItem> items) {
+		this.id = id;
+		this.customerId = customerId;
+		this.orderDate = orderDate;
+		this.items = items;
+	}
+
+	public Order addItem(LineItem item) {
+
+		List<LineItem> newItems = new ArrayList<LineItem>(items != null ? items : Collections.<LineItem> emptyList());
+		newItems.add(item);
+
+		return new Order(id, customerId, orderDate, newItems);
+	}
+
+	public String getId() {
+		return id;
+	}
+
+	public String getCustomerId() {
+		return customerId;
+	}
+
+	public Date getOrderDate() {
+		return orderDate;
+	}
+
+	public List<LineItem> getItems() {
+		return items;
+	}
+}

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/SpelExpressionTransformerUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2014 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.
@@ -21,6 +21,7 @@ import static org.junit.Assert.*;
 import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Test;
+import org.springframework.data.mongodb.core.Person;
 
 /**
  * Unit tests for {@link SpelExpressionTransformer}.
@@ -174,6 +175,26 @@ public class SpelExpressionTransformerUnitTests {
 				is("{ \"$multiply\" : [ { \"$add\" : [ 1 , 42 , 1.2345]} , 23]}"));
 	}
 
+	/**
+	 * @see DATAMONGO-840
+	 */
+	@Test
+	public void shouldRenderCompoundExpressionsWithIndexerAndFieldReference() {
+
+		Person person = new Person();
+		person.setAge(10);
+		assertThat(transform("[0].age + a.c", person), is("{ \"$add\" : [ 10 , \"$a.c\"]}"));
+	}
+
+	/**
+	 * @see DATAMONGO-840
+	 */
+	@Test
+	public void shouldRenderCompoundExpressionsWithOnlyFieldReferences() {
+
+		assertThat(transform("a.b + a.c"), is("{ \"$add\" : [ \"$a.b\" , \"$a.c\"]}"));
+	}
+
 	@Test
 	public void shouldRenderStringFunctions() {