DATAMONGO-1326 - Add support for $lookup to aggregation.

Original Pull Request: #344
CLA: 164120160221125037 (Alessio Fachechi)

Author: alessiofachechi

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

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2013 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;
+
+/**
+ * {@link AggregationOperation} that exposes <b>additional</b> {@link ExposedFields} that can be used for later
+ * aggregation pipeline {@code AggregationOperation}s, e.g. lookup operation produces a field which has to be added to
+ * the current ones.
+ *
+ * @author Alessio Fachechi
+ */
+public interface AdditionalFieldsExposingAggregationOperation extends FieldsExposingAggregationOperation {
+
+}

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

@@ -37,10 +37,11 @@
 /**
  * An {@code Aggregation} is a representation of a list of aggregation steps to be performed by the MongoDB Aggregation
  * Framework.
- * 
+ *
  * @author Tobias Trelle
  * @author Thomas Darimont
  * @author Oliver Gierke
+ * @author Alessio Fachechi
  * @since 1.3
  */
 public class Aggregation {
@@ -65,7 +66,7 @@ public class Aggregation {
 
 	/**
 	 * Creates a new {@link Aggregation} from the given {@link AggregationOperation}s.
-	 * 
+	 *
 	 * @param operations must not be {@literal null} or empty.
 	 */
 	public static Aggregation newAggregation(List<? extends AggregationOperation> operations) {
@@ -74,7 +75,7 @@ public static Aggregation newAggregation(List<? extends AggregationOperation> op
 
 	/**
 	 * Creates a new {@link Aggregation} from the given {@link AggregationOperation}s.
-	 * 
+	 *
 	 * @param operations must not be {@literal null} or empty.
 	 */
 	public static Aggregation newAggregation(AggregationOperation... operations) {
@@ -84,7 +85,7 @@ public static Aggregation newAggregation(AggregationOperation... operations) {
 	/**
 	 * Returns a copy of this {@link Aggregation} with the given {@link AggregationOptions} set. Note that options are
 	 * supported in MongoDB version 2.6+.
-	 * 
+	 *
 	 * @param options must not be {@literal null}.
 	 * @return
 	 * @since 1.6
@@ -97,7 +98,7 @@ public Aggregation withOptions(AggregationOptions options) {
 
 	/**
 	 * Creates a new {@link TypedAggregation} for the given type and {@link AggregationOperation}s.
-	 * 
+	 *
 	 * @param type must not be {@literal null}.
 	 * @param operations must not be {@literal null} or empty.
 	 */
@@ -107,7 +108,7 @@ public static <T> TypedAggregation<T> newAggregation(Class<T> type, List<? exten
 
 	/**
 	 * Creates a new {@link TypedAggregation} for the given type and {@link AggregationOperation}s.
-	 * 
+	 *
 	 * @param type must not be {@literal null}.
 	 * @param operations must not be {@literal null} or empty.
 	 */
@@ -117,7 +118,7 @@ public static <T> TypedAggregation<T> newAggregation(Class<T> type, AggregationO
 
 	/**
 	 * Creates a new {@link Aggregation} from the given {@link AggregationOperation}s.
-	 * 
+	 *
 	 * @param aggregationOperations must not be {@literal null} or empty.
 	 */
 	protected Aggregation(AggregationOperation... aggregationOperations) {
@@ -137,7 +138,7 @@ protected static List<AggregationOperation> asAggregationList(AggregationOperati
 
 	/**
 	 * Creates a new {@link Aggregation} from the given {@link AggregationOperation}s.
-	 * 
+	 *
 	 * @param aggregationOperations must not be {@literal null} or empty.
 	 */
 	protected Aggregation(List<AggregationOperation> aggregationOperations) {
@@ -146,7 +147,7 @@ protected Aggregation(List<AggregationOperation> aggregationOperations) {
 
 	/**
 	 * Creates a new {@link Aggregation} from the given {@link AggregationOperation}s.
-	 * 
+	 *
 	 * @param aggregationOperations must not be {@literal null} or empty.
 	 * @param options must not be {@literal null} or empty.
 	 */
@@ -162,7 +163,7 @@ protected Aggregation(List<AggregationOperation> aggregationOperations, Aggregat
 
 	/**
 	 * A pointer to the previous {@link AggregationOperation}.
-	 * 
+	 *
 	 * @return
 	 */
 	public static String previousOperation() {
@@ -171,7 +172,7 @@ public static String previousOperation() {
 
 	/**
 	 * Creates a new {@link ProjectionOperation} including the given fields.
-	 * 
+	 *
 	 * @param fields must not be {@literal null}.
 	 * @return
 	 */
@@ -181,7 +182,7 @@ public static ProjectionOperation project(String... fields) {
 
 	/**
 	 * Creates a new {@link ProjectionOperation} includeing the given {@link Fields}.
-	 * 
+	 *
 	 * @param fields must not be {@literal null}.
 	 * @return
 	 */
@@ -191,7 +192,7 @@ public static ProjectionOperation project(Fields fields) {
 
 	/**
 	 * Factory method to create a new {@link UnwindOperation} for the field with the given name.
-	 * 
+	 *
 	 * @param fieldName must not be {@literal null} or empty.
 	 * @return
 	 */
@@ -201,7 +202,7 @@ public static UnwindOperation unwind(String field) {
 
 	/**
 	 * Creates a new {@link GroupOperation} for the given fields.
-	 * 
+	 *
 	 * @param fields must not be {@literal null}.
 	 * @return
 	 */
@@ -211,7 +212,7 @@ public static GroupOperation group(String... fields) {
 
 	/**
 	 * Creates a new {@link GroupOperation} for the given {@link Fields}.
-	 * 
+	 *
 	 * @param fields must not be {@literal null}.
 	 * @return
 	 */
@@ -221,7 +222,7 @@ public static GroupOperation group(Fields fields) {
 
 	/**
 	 * Factory method to create a new {@link SortOperation} for the given {@link Sort}.
-	 * 
+	 *
 	 * @param sort must not be {@literal null}.
 	 * @return
 	 */
@@ -231,7 +232,7 @@ public static SortOperation sort(Sort sort) {
 
 	/**
 	 * Factory method to create a new {@link SortOperation} for the given sort {@link Direction} and {@code fields}.
-	 * 
+	 *
 	 * @param direction must not be {@literal null}.
 	 * @param fields must not be {@literal null}.
 	 * @return
@@ -242,7 +243,7 @@ public static SortOperation sort(Direction direction, String... fields) {
 
 	/**
 	 * Creates a new {@link SkipOperation} skipping the given number of elements.
-	 * 
+	 *
 	 * @param elementsToSkip must not be less than zero.
 	 * @return
 	 */
@@ -252,7 +253,7 @@ public static SkipOperation skip(int elementsToSkip) {
 
 	/**
 	 * Creates a new {@link LimitOperation} limiting the result to the given number of elements.
-	 * 
+	 *
 	 * @param maxElements must not be less than zero.
 	 * @return
 	 */
@@ -262,28 +263,48 @@ public static LimitOperation limit(long maxElements) {
 
 	/**
 	 * Creates a new {@link MatchOperation} using the given {@link Criteria}.
-	 * 
+	 *
 	 * @param criteria must not be {@literal null}.
 	 * @return
 	 */
 	public static MatchOperation match(Criteria criteria) {
 		return new MatchOperation(criteria);
 	}
 
+	/**
+	 * Creates a new {@link LookupOperation} for the given fields.
+	 *
+	 * @param fields must not be {@literal null}.
+	 * @return
+	 */
+	public static LookupOperation lookup(String from, String localField, String foreignField, String as) {
+		return lookup(field(from), field(localField), field(foreignField), field(as));
+	}
+
+	/**
+	 * Creates a new {@link LookupOperation} for the given {@link Fields}.
+	 *
+	 * @param fields must not be {@literal null}.
+	 * @return
+	 */
+	public static LookupOperation lookup(Field from, Field localField, Field foreignField, Field as) {
+		return new LookupOperation(from, localField, foreignField, as);
+	}
+
 	/**
 	 * Creates a new {@link Fields} instance for the given field names.
-	 * 
-	 * @see Fields#fields(String...)
+	 *
 	 * @param fields must not be {@literal null}.
 	 * @return
+	 * @see Fields#fields(String...)
 	 */
 	public static Fields fields(String... fields) {
 		return Fields.fields(fields);
 	}
 
 	/**
 	 * Creates a new {@link Fields} instance from the given field name and target reference.
-	 * 
+	 *
 	 * @param name must not be {@literal null} or empty.
 	 * @param target must not be {@literal null} or empty.
 	 * @return
@@ -295,7 +316,7 @@ public static Fields bind(String name, String target) {
 	/**
 	 * Creates a new {@link GeoNearOperation} instance from the given {@link NearQuery} and the{@code distanceField}. The
 	 * {@code distanceField} defines output field that contains the calculated distance.
-	 * 
+	 *
 	 * @param query must not be {@literal null}.
 	 * @param distanceField must not be {@literal null} or empty.
 	 * @return
@@ -307,7 +328,7 @@ public static GeoNearOperation geoNear(NearQuery query, String distanceField) {
 
 	/**
 	 * Returns a new {@link AggregationOptions.Builder}.
-	 * 
+	 *
 	 * @return
 	 * @since 1.6
 	 */
@@ -317,7 +338,7 @@ public static AggregationOptions.Builder newAggregationOptions() {
 
 	/**
 	 * Converts this {@link Aggregation} specification to a {@link DBObject}.
-	 * 
+	 *
 	 * @param inputCollectionName the name of the input collection
 	 * @return the {@code DBObject} representing this aggregation
 	 */
@@ -331,8 +352,11 @@ public DBObject toDbObject(String inputCollectionName, AggregationOperationConte
 			operationDocuments.add(operation.toDBObject(context));
 
 			if (operation instanceof FieldsExposingAggregationOperation) {
+				boolean additional = operation instanceof AdditionalFieldsExposingAggregationOperation ? true : false;
+
 				FieldsExposingAggregationOperation exposedFieldsOperation = (FieldsExposingAggregationOperation) operation;
-				context = new ExposedFieldsAggregationOperationContext(exposedFieldsOperation.getFields(), rootContext);
+				context = new ExposedFieldsAggregationOperationContext(exposedFieldsOperation.getFields(), rootContext,
+						additional);
 			}
 		}
 
@@ -356,7 +380,7 @@ public String toString() {
 
 	/**
 	 * Simple {@link AggregationOperationContext} that just returns {@link FieldReference}s as is.
-	 * 
+	 *
 	 * @author Oliver Gierke
 	 */
 	private static class NoOpAggregationOperationContext implements AggregationOperationContext {
@@ -391,7 +415,7 @@ public FieldReference getReference(String name) {
 
 	/**
 	 * Describes the system variables available in MongoDB aggregation framework pipeline expressions.
-	 * 
+	 *
 	 * @author Thomas Darimont
 	 * @see http://docs.mongodb.org/manual/reference/aggregation-variables
 	 */
@@ -404,7 +428,7 @@ enum SystemVariable {
 		/**
 		 * Return {@literal true} if the given {@code fieldRef} denotes a well-known system variable, {@literal false}
 		 * otherwise.
-		 * 
+		 *
 		 * @param fieldRef may be {@literal null}.
 		 * @return
 		 */