DATAMONGO-861 - Polishing.

Favor usage of List over BasicDBList.
Rename ProjectionOperation.transform to applyCondition.
Add missing author and since tags, remove trailing white spaces and fix reference documentation headline clash.

Original Pull Request: #385

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

@@ -25,7 +25,7 @@ import org.springframework.data.domain.Sort;
 import org.springframework.data.domain.Sort.Direction;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.ExposedField;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
-import org.springframework.data.mongodb.core.aggregation.Fields.*;
+import org.springframework.data.mongodb.core.aggregation.Fields.AggregationField;
 import org.springframework.data.mongodb.core.aggregation.FieldsExposingAggregationOperation.InheritsFieldsAggregationOperation;
 import org.springframework.data.mongodb.core.query.Criteria;
 import org.springframework.data.mongodb.core.query.NearQuery;
@@ -331,13 +331,13 @@ public class Aggregation {
 	}
 
 	/**
-	 * Creates a new {@link OutOperation} using the given collection name. This operation must be the last operation
-	 * in the pipeline.
+	 * Creates a new {@link OutOperation} using the given collection name. This operation must be the last operation in
+	 * the pipeline.
 	 *
 	 * @param outCollectionName collection name to export aggregation results. The {@link OutOperation} creates a new
-	 * collection in the current database if one does not already exist. The collection is
-	 * not visible until the aggregation completes. If the aggregation fails, MongoDB does
-	 * not create the collection. Must not be {@literal null}.
+	 *          collection in the current database if one does not already exist. The collection is not visible until the
+	 *          aggregation completes. If the aggregation fails, MongoDB does not create the collection. Must not be
+	 *          {@literal null}.
 	 * @return
 	 */
 	public static OutOperation out(String outCollectionName) {

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

@@ -15,12 +15,14 @@
  */
 package org.springframework.data.mongodb.core.aggregation;
 
+import java.util.ArrayList;
+import java.util.List;
+
 import org.springframework.dao.InvalidDataAccessApiUsageException;
 import org.springframework.data.mongodb.core.query.CriteriaDefinition;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
-import com.mongodb.BasicDBList;
 import com.mongodb.BasicDBObject;
 import com.mongodb.DBObject;
 
@@ -32,6 +34,7 @@ import com.mongodb.DBObject;
  * 
  * @see http://docs.mongodb.com/manual/reference/operator/aggregation/cond/
  * @author Mark Paluch
+ * @author Christoph Strobl
  * @since 1.10
  */
 public class ConditionalOperator implements AggregationExpression {
@@ -42,7 +45,7 @@ public class ConditionalOperator implements AggregationExpression {
 
 	/**
 	 * Creates a new {@link ConditionalOperator} for a given {@link Field} and {@code then}/{@code otherwise} values.
-	 * 
+	 *
 	 * @param condition must not be {@literal null}.
 	 * @param thenValue must not be {@literal null}.
 	 * @param otherwiseValue must not be {@literal null}.
@@ -116,8 +119,7 @@ public class ConditionalOperator implements AggregationExpression {
 			return ((ConditionalOperator) value).toDbObject(context);
 		}
 
-		DBObject toMap = context.getMappedObject(new BasicDBObject("$set", value));
-		return toMap.get("$set");
+		return context.getMappedObject(new BasicDBObject("$set", value)).get("$set");
 	}
 
 	private Object resolveCriteria(AggregationOperationContext context, Object value) {
@@ -129,7 +131,7 @@ public class ConditionalOperator implements AggregationExpression {
 		if (value instanceof CriteriaDefinition) {
 
 			DBObject mappedObject = context.getMappedObject(((CriteriaDefinition) value).getCriteriaObject());
-			BasicDBList clauses = new BasicDBList();
+			List<Object> clauses = new ArrayList<Object>();
 
 			clauses.addAll(getClauses(context, mappedObject));
 
@@ -144,9 +146,9 @@ public class ConditionalOperator implements AggregationExpression {
 				String.format("Invalid value in condition. Supported: DBObject, Field references, Criteria, got: %s", value));
 	}
 
-	private BasicDBList getClauses(AggregationOperationContext context, DBObject mappedObject) {
+	private List<Object> getClauses(AggregationOperationContext context, DBObject mappedObject) {
 
-		BasicDBList clauses = new BasicDBList();
+		List<Object> clauses = new ArrayList<Object>();
 
 		for (String key : mappedObject.keySet()) {
 
@@ -157,15 +159,17 @@ public class ConditionalOperator implements AggregationExpression {
 		return clauses;
 	}
 
-	private BasicDBList getClauses(AggregationOperationContext context, String key, Object predicate) {
+	private List<Object> getClauses(AggregationOperationContext context, String key, Object predicate) {
 
-		BasicDBList clauses = new BasicDBList();
+		List<Object> clauses = new ArrayList<Object>();
 
-		if (predicate instanceof BasicDBList) {
+		if (predicate instanceof List) {
 
-			BasicDBList args = new BasicDBList();
-			for (Object clause : (BasicDBList) predicate) {
-				args.addAll(getClauses(context, (BasicDBObject) clause));
+			List<Object> args = new ArrayList<Object>();
+			for (Object clause : (List<?>) predicate) {
+				if (clause instanceof DBObject) {
+					args.addAll(getClauses(context, (DBObject) clause));
+				}
 			}
 
 			clauses.add(new BasicDBObject(key, args));
@@ -180,7 +184,7 @@ public class ConditionalOperator implements AggregationExpression {
 					continue;
 				}
 
-				BasicDBList args = new BasicDBList();
+				List<Object> args = new ArrayList<Object>();
 				args.add("$" + key);
 				args.add(nested.get(s));
 				clauses.add(new BasicDBObject(s, args));
@@ -188,7 +192,7 @@ public class ConditionalOperator implements AggregationExpression {
 
 		} else if (!isKeyword(key)) {
 
-			BasicDBList args = new BasicDBList();
+			List<Object> args = new ArrayList<Object>();
 			args.add("$" + key);
 			args.add(predicate);
 			clauses.add(new BasicDBObject("$eq", args));
@@ -230,6 +234,9 @@ public class ConditionalOperator implements AggregationExpression {
 		return ConditionalExpressionBuilder.newBuilder();
 	}
 
+	/**
+	 * @since 1.10
+	 */
 	public static interface WhenBuilder {
 
 		/**
@@ -257,6 +264,9 @@ public class ConditionalOperator implements AggregationExpression {
 		ThenBuilder when(CriteriaDefinition criteria);
 	}
 
+	/**
+	 * @since 1.10
+	 */
 	public static interface ThenBuilder {
 
 		/**
@@ -268,6 +278,9 @@ public class ConditionalOperator implements AggregationExpression {
 		OtherwiseBuilder then(Object value);
 	}
 
+	/**
+	 * @since 1.10
+	 */
 	public static interface OtherwiseBuilder {
 
 		/**
@@ -314,7 +327,7 @@ public class ConditionalOperator implements AggregationExpression {
 			return this;
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.ConditionalOperator.WhenBuilder#when(org.springframework.data.mongodb.core.query.CriteriaDefinition)
 		 */
@@ -327,7 +340,7 @@ public class ConditionalOperator implements AggregationExpression {
 			return this;
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.ConditionalOperator.WhenBuilder#when(org.springframework.data.mongodb.core.aggregation.Field)
 		 */
@@ -340,7 +353,7 @@ public class ConditionalOperator implements AggregationExpression {
 			return this;
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.ConditionalOperator.WhenBuilder#when(java.lang.String)
 		 */
@@ -353,7 +366,7 @@ public class ConditionalOperator implements AggregationExpression {
 			return this;
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.ConditionalOperator.ThenBuilder#then(java.lang.Object)
 		 */
@@ -366,7 +379,7 @@ public class ConditionalOperator implements AggregationExpression {
 			return this;
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.ConditionalOperator.OtherwiseBuilder#otherwise(java.lang.Object)
 		 */

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

@@ -16,16 +16,18 @@
 
 package org.springframework.data.mongodb.core.aggregation;
 
+import java.util.ArrayList;
+import java.util.List;
+
 import org.springframework.util.Assert;
 
-import com.mongodb.BasicDBList;
 import com.mongodb.BasicDBObject;
 import com.mongodb.DBObject;
 
 /**
  * Encapsulates the aggregation framework {@code $ifNull} operator. Replacement values can be either {@link Field field
  * references}, values of simple MongoDB types or values that can be converted to a simple MongoDB type.
- * 
+ *
  * @see http://docs.mongodb.com/manual/reference/operator/aggregation/ifNull/
  * @author Mark Paluch
  * @since 1.10
@@ -37,7 +39,7 @@ public class IfNullOperator implements AggregationExpression {
 
 	/**
 	 * Creates a new {@link IfNullOperator} for the given {@link Field} and replacement {@code value}.
-	 * 
+	 *
 	 * @param field must not be {@literal null}.
 	 * @param value must not be {@literal null}.
 	 */
@@ -50,28 +52,32 @@ public class IfNullOperator implements AggregationExpression {
 		this.value = value;
 	}
 
-	/* 
+	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationExpression#toDbObject(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)
 	 */
 	@Override
 	public DBObject toDbObject(AggregationOperationContext context) {
 
-		BasicDBList list = new BasicDBList();
+		List<Object> list = new ArrayList<Object>();
 
 		list.add(context.getReference(field).toString());
-
-		if (value instanceof Field) {
-			list.add(context.getReference((Field) value).toString());
-		} else {
-
-			DBObject toMap = context.getMappedObject(new BasicDBObject("$set", value));
-			list.add(toMap.get("$set"));
-		}
+		list.add(resolve(value, context));
 
 		return new BasicDBObject("$ifNull", list);
 	}
 
+	private Object resolve(Object value, AggregationOperationContext context) {
+
+		if (value instanceof Field) {
+			return context.getReference((Field) value).toString();
+		} else if (value instanceof DBObject) {
+			return value;
+		}
+
+		return context.getMappedObject(new BasicDBObject("$set", value)).get("$set");
+	}
+
 	/**
 	 * Get a builder that allows fluent creation of {@link IfNullOperator}.
 	 *
@@ -81,6 +87,9 @@ public class IfNullOperator implements AggregationExpression {
 		return IfNullOperatorBuilder.newBuilder();
 	}
 
+	/**
+	 * @since 1.10
+	 */
 	public static interface IfNullBuilder {
 
 		/**
@@ -96,6 +105,9 @@ public class IfNullOperator implements AggregationExpression {
 		ThenBuilder ifNull(String field);
 	}
 
+	/**
+	 * @since 1.10
+	 */
 	public static interface ThenBuilder {
 
 		/**
@@ -134,11 +146,10 @@ public class IfNullOperator implements AggregationExpression {
 			return new IfNullOperatorBuilder();
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.IfNullOperator.IfNullBuilder#ifNull(org.springframework.data.mongodb.core.aggregation.Field)
 		 */
-
 		public ThenBuilder ifNull(Field field) {
 
 			Assert.notNull(field, "Field must not be null!");
@@ -147,7 +158,7 @@ public class IfNullOperator implements AggregationExpression {
 			return this;
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.IfNullOperator.IfNullBuilder#ifNull(java.lang.String)
 		 */
@@ -159,7 +170,7 @@ public class IfNullOperator implements AggregationExpression {
 			return this;
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.IfNullOperator.ThenReplaceBuilder#thenReplaceWith(org.springframework.data.mongodb.core.aggregation.Field)
 		 */
@@ -171,7 +182,7 @@ public class IfNullOperator implements AggregationExpression {
 			return new IfNullOperator(this.field, replacementField);
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.IfNullOperator.ThenReplaceBuilder#thenReplaceWith(java.lang.Object)
 		 */

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

@@ -42,6 +42,7 @@ import com.mongodb.DBObject;
  * @author Thomas Darimont
  * @author Oliver Gierke
  * @author Christoph Strobl
+ * @author Mark Paluch
  * @since 1.3
  */
 public class ProjectionOperation implements FieldsExposingAggregationOperation {
@@ -244,20 +245,20 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		/**
 		 * Apply a conditional projection using {@link ConditionalOperator}.
 		 *
-		 * @param conditional must not be {@literal null}.
+		 * @param conditionalOperator must not be {@literal null}.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
-		public abstract ProjectionOperation transform(ConditionalOperator conditional);
+		public abstract ProjectionOperation applyCondition(ConditionalOperator conditionalOperator);
 
 		/**
 		 * Apply a conditional value replacement for {@literal null} values using {@link IfNullOperator}.
 		 *
-		 * @param ifNull must not be {@literal null}.
+		 * @param ifNullOperator must not be {@literal null}.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
-		public abstract ProjectionOperation transform(IfNullOperator ifNull);
+		public abstract ProjectionOperation applyCondition(IfNullOperator ifNullOperator);
 	}
 
 	/**
@@ -359,7 +360,8 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 				return new BasicDBObject(getExposedField().getName(), toMongoExpression(context, expression, params));
 			}
 
-			protected static Object toMongoExpression(AggregationOperationContext context, String expression, Object[] params) {
+			protected static Object toMongoExpression(AggregationOperationContext context, String expression,
+					Object[] params) {
 				return TRANSFORMER.transform(expression, context, params);
 			}
 		}
@@ -455,22 +457,26 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 			return this.operation.and(new FieldProjection(Fields.field(alias, name), null));
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.ProjectionOperation.AbstractProjectionOperationBuilder#transform(org.springframework.data.mongodb.core.aggregation.ConditionalOperator)
 		 */
 		@Override
-		public ProjectionOperation transform(ConditionalOperator conditional) {
-			return this.operation.and(new ExpressionProjection(Fields.field(name), conditional));
+		public ProjectionOperation applyCondition(ConditionalOperator conditionalOperator) {
+
+			Assert.notNull(conditionalOperator, "ConditionalOperator must not be null!");
+			return this.operation.and(new ExpressionProjection(Fields.field(name), conditionalOperator));
 		}
 
-		/* 
+		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.ProjectionOperation.AbstractProjectionOperationBuilder#transform(org.springframework.data.mongodb.core.aggregation.IfNullOperator)
 		 */
 		@Override
-		public ProjectionOperation transform(IfNullOperator ifNull) {
-			return this.operation.and(new ExpressionProjection(Fields.field(name), ifNull));
+		public ProjectionOperation applyCondition(IfNullOperator ifNullOperator) {
+
+			Assert.notNull(ifNullOperator, "IfNullOperator must not be null!");
+			return this.operation.and(new ExpressionProjection(Fields.field(name), ifNullOperator));
 		}
 
 		/**

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

@@ -519,7 +519,7 @@ public class AggregationTests {
 		TypedAggregation<InventoryItem> aggregation = newAggregation(InventoryItem.class, //
 				project("item") //
 						.and("discount")//
-						.transform(ConditionalOperator.newBuilder().when(Criteria.where("qty").gte(250)) //
+						.applyCondition(ConditionalOperator.newBuilder().when(Criteria.where("qty").gte(250)) //
 								.then(30) //
 								.otherwise(20)));
 
@@ -594,7 +594,7 @@ public class AggregationTests {
 		TypedAggregation<ZipInfo> aggregation = newAggregation(ZipInfo.class, //
 				project() //
 						.and("largePopulation")//
-						.transform(ConditionalOperator.newBuilder().when(Criteria.where("population").gte(20000)) //
+						.applyCondition(ConditionalOperator.newBuilder().when(Criteria.where("population").gte(20000)) //
 								.then(true) //
 								.otherwise(false)) //
 						.and("population").as("population"));
@@ -619,7 +619,7 @@ public class AggregationTests {
 		TypedAggregation<ZipInfo> aggregation = newAggregation(ZipInfo.class, //
 				project() //
 						.and("size")//
-						.transform(ConditionalOperator.newBuilder().when(Criteria.where("population").gte(20000)) //
+						.applyCondition(ConditionalOperator.newBuilder().when(Criteria.where("population").gte(20000)) //
 								.then(ConditionalOperator.newBuilder().when(Criteria.where("population").gte(200000)).then("huge")
 										.otherwise("small")) //
 								.otherwise("small")) //
@@ -648,7 +648,7 @@ public class AggregationTests {
 		TypedAggregation<LineItem> aggregation = newAggregation(LineItem.class, //
 				project("id") //
 						.and("caption")//
-						.transform(ifNull(field("caption"), "unknown")),
+						.applyCondition(ifNull(field("caption"), "unknown")),
 				sort(ASC, "id"));
 
 		assertThat(aggregation.toString(), is(notNullValue()));
@@ -675,7 +675,7 @@ public class AggregationTests {
 		TypedAggregation<LineItem> aggregation = newAggregation(LineItem.class, //
 				project("id") //
 						.and("caption")//
-						.transform(ifNull(field("caption"), field("id"))),
+						.applyCondition(ifNull(field("caption"), field("id"))),
 				sort(ASC, "id"));
 
 		assertThat(aggregation.toString(), is(notNullValue()));
@@ -798,11 +798,12 @@ public class AggregationTests {
 		assertThat((Double) resultList.get(0).get("netPriceMul2"), is(product.netPrice * 2));
 		assertThat((Double) resultList.get(0).get("netPriceDiv119"), is(product.netPrice / 1.19));
 		assertThat((Integer) resultList.get(0).get("spaceUnitsMod2"), is(product.spaceUnits % 2));
-		assertThat((Integer) resultList.get(0).get("spaceUnitsPlusSpaceUnits"), is(product.spaceUnits + product.spaceUnits));
+		assertThat((Integer) resultList.get(0).get("spaceUnitsPlusSpaceUnits"),
+				is(product.spaceUnits + product.spaceUnits));
 		assertThat((Integer) resultList.get(0).get("spaceUnitsMinusSpaceUnits"),
 				is(product.spaceUnits - product.spaceUnits));
-		assertThat((Integer) resultList.get(0).get("spaceUnitsMultiplySpaceUnits"), is(product.spaceUnits
-				* product.spaceUnits));
+		assertThat((Integer) resultList.get(0).get("spaceUnitsMultiplySpaceUnits"),
+				is(product.spaceUnits * product.spaceUnits));
 		assertThat((Double) resultList.get(0).get("spaceUnitsDivideSpaceUnits"),
 				is((double) (product.spaceUnits / product.spaceUnits)));
 		assertThat((Integer) resultList.get(0).get("spaceUnitsModSpaceUnits"), is(product.spaceUnits % product.spaceUnits));
@@ -891,8 +892,8 @@ public class AggregationTests {
 		DBObject firstItem = resultList.get(0);
 		assertThat((String) firstItem.get("_id"), is(product.id));
 		assertThat((String) firstItem.get("name"), is(product.name));
-		assertThat((Double) firstItem.get("salesPrice"), is((product.netPrice * (1 - product.discountRate) + shippingCosts)
-				* (1 + product.taxRate)));
+		assertThat((Double) firstItem.get("salesPrice"),
+				is((product.netPrice * (1 - product.discountRate) + shippingCosts) * (1 + product.taxRate)));
 	}
 
 	@Test
@@ -914,7 +915,7 @@ public class AggregationTests {
 
 	/**
 	 * @see DATAMONGO-753
-	 * @see http 
+	 * @see http
 	 *      ://stackoverflow.com/questions/18653574/spring-data-mongodb-aggregation-framework-invalid-reference-in-group
 	 *      -operati
 	 */
@@ -944,7 +945,7 @@ public class AggregationTests {
 
 	/**
 	 * @see DATAMONGO-753
-	 * @see http 
+	 * @see http
 	 *      ://stackoverflow.com/questions/18653574/spring-data-mongodb-aggregation-framework-invalid-reference-in-group
 	 *      -operati
 	 */
@@ -979,12 +980,13 @@ public class AggregationTests {
 		data.stringValue = "ABC";
 		mongoTemplate.insert(data);
 
-		TypedAggregation<Data> agg = newAggregation(Data.class, project() //
-				.andExpression("concat(stringValue, 'DE')").as("concat") //
-				.andExpression("strcasecmp(stringValue,'XYZ')").as("strcasecmp") //
-				.andExpression("substr(stringValue,1,1)").as("substr") //
-				.andExpression("toLower(stringValue)").as("toLower") //
-				.andExpression("toUpper(toLower(stringValue))").as("toUpper") //
+		TypedAggregation<Data> agg = newAggregation(Data.class,
+				project() //
+						.andExpression("concat(stringValue, 'DE')").as("concat") //
+						.andExpression("strcasecmp(stringValue,'XYZ')").as("strcasecmp") //
+						.andExpression("substr(stringValue,1,1)").as("substr") //
+						.andExpression("toLower(stringValue)").as("toLower") //
+						.andExpression("toUpper(toLower(stringValue))").as("toUpper") //
 		);
 
 		AggregationResults<DBObject> results = mongoTemplate.aggregate(agg, DBObject.class);
@@ -1010,17 +1012,18 @@ public class AggregationTests {
 		data.dateValue = new SimpleDateFormat("dd.MM.yyyy HH:mm:ss.SSSZ").parse("29.08.1983 12:34:56.789+0000");
 		mongoTemplate.insert(data);
 
-		TypedAggregation<Data> agg = newAggregation(Data.class, project() //
-				.andExpression("dayOfYear(dateValue)").as("dayOfYear") //
-				.andExpression("dayOfMonth(dateValue)").as("dayOfMonth") //
-				.andExpression("dayOfWeek(dateValue)").as("dayOfWeek") //
-				.andExpression("year(dateValue)").as("year") //
-				.andExpression("month(dateValue)").as("month") //
-				.andExpression("week(dateValue)").as("week") //
-				.andExpression("hour(dateValue)").as("hour") //
-				.andExpression("minute(dateValue)").as("minute") //
-				.andExpression("second(dateValue)").as("second") //
-				.andExpression("millisecond(dateValue)").as("millisecond") //
+		TypedAggregation<Data> agg = newAggregation(Data.class,
+				project() //
+						.andExpression("dayOfYear(dateValue)").as("dayOfYear") //
+						.andExpression("dayOfMonth(dateValue)").as("dayOfMonth") //
+						.andExpression("dayOfWeek(dateValue)").as("dayOfWeek") //
+						.andExpression("year(dateValue)").as("year") //
+						.andExpression("month(dateValue)").as("month") //
+						.andExpression("week(dateValue)").as("week") //
+						.andExpression("hour(dateValue)").as("hour") //
+						.andExpression("minute(dateValue)").as("minute") //
+						.andExpression("second(dateValue)").as("second") //
+						.andExpression("millisecond(dateValue)").as("millisecond") //
 		);
 
 		AggregationResults<DBObject> results = mongoTemplate.aggregate(agg, DBObject.class);
@@ -1132,7 +1135,7 @@ public class AggregationTests {
 						.and("orderId").previousOperation() //
 						.andExpression("netAmount * [0]", taxRate).as("taxAmount") //
 						.andExpression("netAmount * (1 + [0])", taxRate).as("totalAmount") //
-				), Invoice.class);
+		), Invoice.class);
 
 		Invoice invoice = results.getUniqueMappedResult();
 
@@ -1723,12 +1726,14 @@ public class AggregationTests {
 		public InventoryItem() {}
 
 		public InventoryItem(int id, String item, int qty) {
+
 			this.id = id;
 			this.item = item;
 			this.qty = qty;
 		}
 
 		public InventoryItem(int id, String item, String description, int qty) {
+
 			this.id = id;
 			this.item = item;
 			this.description = description;

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

@@ -24,6 +24,7 @@ import static org.springframework.data.mongodb.core.query.Criteria.*;
 import static org.springframework.data.mongodb.test.util.IsBsonObject.*;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 import org.junit.Rule;
@@ -31,9 +32,7 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.springframework.data.domain.Sort.Direction;
 import org.springframework.data.mongodb.core.query.Criteria;
-import org.springframework.data.mongodb.test.util.BasicDbListBuilder;
 
-import com.mongodb.BasicDBList;
 import com.mongodb.BasicDBObject;
 import com.mongodb.BasicDBObjectBuilder;
 import com.mongodb.DBObject;
@@ -247,25 +246,6 @@ public class AggregationUnitTests {
 		assertThat(fields.get("foosum"), is((Object) new BasicDBObject("$sum", "$foo")));
 	}
 
-	/**
-	 * @see DATAMONGO-861
-	 */
-	@Test
-	public void conditionExpressionBasedFieldsShouldBeReferencableInFollowingOperations() {
-
-		DBObject agg = newAggregation( //
-				project("a"), //
-				group("a").first(conditional(Criteria.where("a").gte(42), "answer", "no-answer")).as("foosum") //
-		).toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
-
-		@SuppressWarnings("unchecked")
-		DBObject secondProjection = ((List<DBObject>) agg.get("pipeline")).get(1);
-		DBObject fields = getAsDBObject(secondProjection, "$group");
-		assertThat(getAsDBObject(fields, "foosum"), isBsonObject().containing("$first"));
-		assertThat(getAsDBObject(fields, "foosum"), isBsonObject().containing("$first.$cond.then", "answer"));
-		assertThat(getAsDBObject(fields, "foosum"), isBsonObject().containing("$first.$cond.else", "no-answer"));
-	}
-
 	/**
 	 * @see DATAMONGO-908
 	 */
@@ -331,15 +311,16 @@ public class AggregationUnitTests {
 		DBObject agg = newAggregation( //
 				project().and("a").as("aa") //
 		) //
-		.withOptions(aggregationOptions) //
+				.withOptions(aggregationOptions) //
 				.toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
-		assertThat(agg.toString(), is("{ \"aggregate\" : \"foo\" , " //
-				+ "\"pipeline\" : [ { \"$project\" : { \"aa\" : \"$a\"}}] , " //
-				+ "\"allowDiskUse\" : true , " //
-				+ "\"explain\" : true , " //
-				+ "\"cursor\" : { \"foo\" : 1}}" //
-		));
+		assertThat(agg.toString(),
+				is("{ \"aggregate\" : \"foo\" , " //
+						+ "\"pipeline\" : [ { \"$project\" : { \"aa\" : \"$a\"}}] , " //
+						+ "\"allowDiskUse\" : true , " //
+						+ "\"explain\" : true , " //
+						+ "\"cursor\" : { \"foo\" : 1}}" //
+				));
 	}
 
 	/**
@@ -357,8 +338,8 @@ public class AggregationUnitTests {
 		).toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject projection0 = extractPipelineElement(agg, 0, "$project");
-		assertThat(projection0, is((DBObject) new BasicDBObject("someKey", 1).append("a1", "$a")
-				.append("a2", "$$CURRENT.a")));
+		assertThat(projection0,
+				is((DBObject) new BasicDBObject("someKey", 1).append("a1", "$a").append("a2", "$$CURRENT.a")));
 
 		DBObject sort = extractPipelineElement(agg, 1, "$sort");
 		assertThat(sort, is((DBObject) new BasicDBObject("a", -1)));
@@ -379,7 +360,7 @@ public class AggregationUnitTests {
 						.and("tags").minus(10).as("tags_count")//
 				, group("date")//
 						.sum("tags_count").as("count")//
-				).toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
+		).toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject group = extractPipelineElement(agg, 1, "$group");
 		assertThat(getAsDBObject(group, "count"), is(new BasicDBObjectBuilder().add("$sum", "$tags_count").get()));
@@ -396,12 +377,31 @@ public class AggregationUnitTests {
 						.andExpression("tags-10")//
 				, group("date")//
 						.sum("tags_count").as("count")//
-				).toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
+		).toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject group = extractPipelineElement(agg, 1, "$group");
 		assertThat(getAsDBObject(group, "count"), is(new BasicDBObjectBuilder().add("$sum", "$tags_count").get()));
 	}
 
+	/**
+	 * @see DATAMONGO-861
+	 */
+	@Test
+	public void conditionExpressionBasedFieldsShouldBeReferencableInFollowingOperations() {
+
+		DBObject agg = newAggregation( //
+				project("a"), //
+				group("a").first(conditional(Criteria.where("a").gte(42), "answer", "no-answer")).as("foosum") //
+		).toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
+
+		@SuppressWarnings("unchecked")
+		DBObject secondProjection = ((List<DBObject>) agg.get("pipeline")).get(1);
+		DBObject fields = getAsDBObject(secondProjection, "$group");
+		assertThat(getAsDBObject(fields, "foosum"), isBsonObject().containing("$first"));
+		assertThat(getAsDBObject(fields, "foosum"), isBsonObject().containing("$first.$cond.then", "answer"));
+		assertThat(getAsDBObject(fields, "foosum"), isBsonObject().containing("$first.$cond.else", "no-answer"));
+	}
+
 	/**
 	 * @see DATAMONGO-861
 	 */
@@ -432,7 +432,7 @@ public class AggregationUnitTests {
 
 		DBObject agg = Aggregation.newAggregation(//
 				project().and("color")
-						.transform(ConditionalOperator.newBuilder() //
+						.applyCondition(ConditionalOperator.newBuilder() //
 								.when("isYellow") //
 								.then("bright") //
 								.otherwise("dark")))
@@ -456,12 +456,12 @@ public class AggregationUnitTests {
 		DBObject agg = Aggregation
 				.newAggregation(project()//
 						.and("color")//
-						.transform(conditional(Criteria.where("key").gt(5), "bright", "dark"))) //
+						.applyCondition(conditional(Criteria.where("key").gt(5), "bright", "dark"))) //
 				.toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject project = extractPipelineElement(agg, 0, "$project");
 		DBObject expectedCondition = new BasicDBObject() //
-				.append("if", new BasicDBObject("$gt", new BasicDbListBuilder().add("$key").add(5).get())) //
+				.append("if", new BasicDBObject("$gt", Arrays.<Object> asList("$key", 5))) //
 				.append("then", "bright") //
 				.append("else", "dark");
 
@@ -478,7 +478,7 @@ public class AggregationUnitTests {
 				.newAggregation(//
 						project().and("color").as("chroma"),
 						project().and("luminosity") //
-								.transform(conditional(field("chroma"), "bright", "dark"))) //
+								.applyCondition(conditional(field("chroma"), "bright", "dark"))) //
 				.toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject project = extractPipelineElement(agg, 1, "$project");
@@ -500,12 +500,12 @@ public class AggregationUnitTests {
 				.newAggregation(//
 						project().and("color").as("chroma"),
 						project().and("luminosity") //
-								.transform(conditional(Criteria.where("chroma").is(100), "bright", "dark"))) //
+								.applyCondition(conditional(Criteria.where("chroma").is(100), "bright", "dark"))) //
 				.toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject project = extractPipelineElement(agg, 1, "$project");
 		DBObject expectedCondition = new BasicDBObject() //
-				.append("if", new BasicDBObject("$eq", new BasicDbListBuilder().add("$chroma").add(100).get())) //
+				.append("if", new BasicDBObject("$eq", Arrays.<Object> asList("$chroma", 100))) //
 				.append("then", "bright") //
 				.append("else", "dark");
 
@@ -522,16 +522,13 @@ public class AggregationUnitTests {
 				.newAggregation(//
 						project().and("color"), //
 						project().and("luminosity") //
-								.transform(ifNull(field("chroma"), "unknown"))) //
+								.applyCondition(ifNull(field("chroma"), "unknown"))) //
 				.toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject project = extractPipelineElement(agg, 1, "$project");
-		BasicDBList expectedCondition = new BasicDbListBuilder() //
-				.add("$chroma") //
-				.add("unknown")//
-				.get();
 
-		assertThat(getAsDBObject(project, "luminosity"), isBsonObject().containing("$ifNull", expectedCondition));
+		assertThat(getAsDBObject(project, "luminosity"),
+				isBsonObject().containing("$ifNull", Arrays.<Object> asList("$chroma", "unknown")));
 	}
 
 	/**
@@ -544,16 +541,13 @@ public class AggregationUnitTests {
 				.newAggregation(//
 						project("fallback").and("color").as("chroma"),
 						project().and("luminosity") //
-								.transform(ifNull(field("chroma"), field("fallback")))) //
+								.applyCondition(ifNull(field("chroma"), field("fallback")))) //
 				.toDbObject("foo", Aggregation.DEFAULT_CONTEXT);
 
 		DBObject project = extractPipelineElement(agg, 1, "$project");
-		BasicDBList expectedCondition = new BasicDbListBuilder() //
-				.add("$chroma") //
-				.add("$fallback")//
-				.get();
 
-		assertThat(getAsDBObject(project, "luminosity"), isBsonObject().containing("$ifNull", expectedCondition));
+		assertThat(getAsDBObject(project, "luminosity"),
+				isBsonObject().containing("$ifNull", Arrays.asList("$chroma", "$fallback")));
 	}
 
 	private DBObject extractPipelineElement(DBObject agg, int index, String operation) {

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

@@ -19,9 +19,10 @@ import static org.junit.Assert.*;
 import static org.springframework.data.mongodb.core.aggregation.ConditionalOperator.*;
 import static org.springframework.data.mongodb.test.util.IsBsonObject.*;
 
+import java.util.Arrays;
+
 import org.junit.Test;
 import org.springframework.data.mongodb.core.query.Criteria;
-import org.springframework.data.mongodb.test.util.BasicDbListBuilder;
 
 import com.mongodb.BasicDBObject;
 import com.mongodb.DBObject;
@@ -30,6 +31,7 @@ import com.mongodb.DBObject;
  * Unit tests for {@link ConditionalOperator}.
  *
  * @author Mark Paluch
+ * @author Christoph Strobl
  */
 public class ConditionalOperatorUnitTests {
 
@@ -117,7 +119,7 @@ public class ConditionalOperatorUnitTests {
 		DBObject dbObject = operator.toDbObject(Aggregation.DEFAULT_CONTEXT);
 
 		DBObject expectedCondition = new BasicDBObject() //
-				.append("if", new BasicDBObject("$gte", new BasicDbListBuilder().add("$luminosity").add(100).get())) //
+				.append("if", new BasicDBObject("$gte", Arrays.<Object> asList("$luminosity", 100))) //
 				.append("then", "bright") //
 				.append("else", "dark");
 
@@ -138,14 +140,12 @@ public class ConditionalOperatorUnitTests {
 
 		DBObject dbObject = operator.toDbObject(Aggregation.DEFAULT_CONTEXT);
 
-		BasicDBObject luminosity = new BasicDBObject("$gte", new BasicDbListBuilder().add("$luminosity").add(100).get());
-		BasicDBObject hue = new BasicDBObject("$eq", new BasicDbListBuilder().add("$hue").add(50).get());
-		BasicDBObject saturation = new BasicDBObject("$lt", new BasicDbListBuilder().add("$saturation").add(11).get());
+		BasicDBObject luminosity = new BasicDBObject("$gte", Arrays.<Object> asList("$luminosity", 100));
+		BasicDBObject hue = new BasicDBObject("$eq", Arrays.<Object> asList("$hue", 50));
+		BasicDBObject saturation = new BasicDBObject("$lt", Arrays.<Object> asList("$saturation", 11));
 
 		DBObject expectedCondition = new BasicDBObject() //
-				.append("if",
-						new BasicDbListBuilder().add(luminosity)
-								.add(new BasicDBObject("$and", new BasicDbListBuilder().add(hue).add(saturation).get())).get()) //
+				.append("if", Arrays.<Object> asList(luminosity, new BasicDBObject("$and", Arrays.asList(hue, saturation)))) //
 				.append("then", "bright") //
 				.append("else", "dark");
 
@@ -164,11 +164,11 @@ public class ConditionalOperatorUnitTests {
 
 		DBObject dbObject = operator.toDbObject(Aggregation.DEFAULT_CONTEXT);
 
-		BasicDBObject gte = new BasicDBObject("$gte", new BasicDbListBuilder().add("$luminosity").add(100).get());
-		BasicDBObject is = new BasicDBObject("$eq", new BasicDbListBuilder().add("$chroma").add(200).get());
+		BasicDBObject gte = new BasicDBObject("$gte", Arrays.<Object> asList("$luminosity", 100));
+		BasicDBObject is = new BasicDBObject("$eq", Arrays.<Object> asList("$chroma", 200));
 
 		DBObject expectedCondition = new BasicDBObject() //
-				.append("if", new BasicDbListBuilder().add(gte).add(is).get()) //
+				.append("if", Arrays.asList(gte, is)) //
 				.append("then", "bright") //
 				.append("else", "dark");
 
@@ -195,12 +195,12 @@ public class ConditionalOperatorUnitTests {
 		DBObject dbObject = operator.toDbObject(Aggregation.DEFAULT_CONTEXT);
 
 		DBObject trueCondition = new BasicDBObject() //
-				.append("if", new BasicDBObject("$gte", new BasicDbListBuilder().add("$luminosity").add(200).get())) //
+				.append("if", new BasicDBObject("$gte", Arrays.<Object> asList("$luminosity", 200))) //
 				.append("then", "verybright") //
 				.append("else", "not-so-bright");
 
 		DBObject falseCondition = new BasicDBObject() //
-				.append("if", new BasicDBObject("$lt", new BasicDbListBuilder().add("$luminosity").add(50).get())) //
+				.append("if", new BasicDBObject("$lt", Arrays.<Object> asList("$luminosity", 50))) //
 				.append("then", "very-dark") //
 				.append("else", "not-so-dark");
 

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

@@ -19,16 +19,17 @@ package org.springframework.data.mongodb.core.aggregation;
 import static org.junit.Assert.*;
 import static org.springframework.data.mongodb.test.util.IsBsonObject.*;
 
-import org.junit.Test;
-import org.springframework.data.mongodb.test.util.BasicDbListBuilder;
+import java.util.Arrays;
+
+import org.junit.Test;
 
-import com.mongodb.BasicDBList;
 import com.mongodb.DBObject;
 
 /**
  * Unit tests for {@link IfNullOperator}.
  *
  * @author Mark Paluch
+ * @author Christoph Strobl
  */
 public class IfNullOperatorUnitTests {
 
@@ -60,12 +61,8 @@ public class IfNullOperatorUnitTests {
 
 		DBObject dbObject = operator.toDbObject(Aggregation.DEFAULT_CONTEXT);
 
-		BasicDBList expected = new BasicDbListBuilder() //
-				.add("$optional") //
-				.add("a more sophisticated value")//
-				.get();
-
-		assertThat(dbObject, isBsonObject().containing("$ifNull", expected));
+		assertThat(dbObject,
+				isBsonObject().containing("$ifNull", Arrays.<Object> asList("$optional", "a more sophisticated value")));
 	}
 
 	/**
@@ -80,11 +77,6 @@ public class IfNullOperatorUnitTests {
 
 		DBObject dbObject = operator.toDbObject(Aggregation.DEFAULT_CONTEXT);
 
-		BasicDBList expected = new BasicDbListBuilder() //
-				.add("$optional") //
-				.add("$never-null")//
-				.get();
-
-		assertThat(dbObject, isBsonObject().containing("$ifNull", expected));
+		assertThat(dbObject, isBsonObject().containing("$ifNull", Arrays.<Object> asList("$optional", "$never-null")));
 	}
 }

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

@@ -291,7 +291,7 @@ public class TypeBasedAggregationOperationContextUnitTests {
 		TypedAggregation<FooPerson> agg = newAggregation(FooPerson.class,
 				project("name") //
 						.and("age") //
-						.transform(conditional(Criteria.where("age.value").lt(10), new Age(0), field("age"))) //
+						.applyCondition(conditional(Criteria.where("age.value").lt(10), new Age(0), field("age"))) //
 		);
 
 		DBObject dbo = agg.toDbObject("person", context);
@@ -317,7 +317,7 @@ public class TypeBasedAggregationOperationContextUnitTests {
 		TypedAggregation<FooPerson> agg = newAggregation(FooPerson.class,
 				project("name") //
 						.and("age") //
-						.transform(ifNull("age", new Age(0))) //
+						.applyCondition(ifNull("age", new Age(0))) //
 		);
 
 		DBObject dbo = agg.toDbObject("person", context);

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/test/util/IsBsonObject.java

@@ -83,7 +83,15 @@ public class IsBsonObject<T extends BSONObject> extends TypeSafeMatcher<T> {
 			}
 
 			if (expectation.type != null && !ClassUtils.isAssignable(expectation.type, o.getClass())) {
-				return false;
+
+				if (o instanceof List) {
+					if (!ClassUtils.isAssignable(List.class, expectation.type)) {
+						return false;
+					}
+				} else {
+					return false;
+				}
+
 			}
 
 			if (expectation.value != null && !new IsEqual<Object>(expectation.value).matches(o)) {

src/main/asciidoc/reference/mongodb.adoc

@@ -1988,8 +1988,8 @@ List<DBObject> resultList = result.getMappedResults();
 
 Note that we can also refer to other fields of the document within the SpEL expression.
 
-[[mongo.aggregation.examples.example6]]
-.Aggregation Framework Example 6
+[[mongo.aggregation.examples.example7]]
+.Aggregation Framework Example 7
 
 This example uses conditional projection. It's derived from the https://docs.mongodb.com/manual/reference/operator/aggregation/cond/[$cond reference documentation].
 
@@ -2019,7 +2019,7 @@ import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
 
 TypedAggregation<InventoryItem> agg = newAggregation(InventoryItem.class,
   project("item").and("discount")
-    .transform(ConditionalOperator.newBuilder().when(Criteria.where("qty").gte(250))
+    .applyCondition(ConditionalOperator.newBuilder().when(Criteria.where("qty").gte(250))
       .then(30)
       .otherwise(20))
     .and(ifNull("description", "Unspecified")).as("description")
@@ -2029,7 +2029,7 @@ AggregationResults<InventoryItemProjection> result = mongoTemplate.aggregate(agg
 List<InventoryItemProjection> stateStatsList = result.getMappedResults();
 ----
 
-* This one-step aggregation uses a projection operation with the `inventory` collection. We project the `discount` field using a conditional transformation for all inventory items that have a `qty` greater or equal to `250`. An second conditional projection is performed for the `description` field. We apply the description `Unspecified` to all items that either do not have a `description` field of items that have a `null` description.
+* This one-step aggregation uses a projection operation with the `inventory` collection. We project the `discount` field using a conditional operation for all inventory items that have a `qty` greater or equal to `250`. An second conditional projection is performed for the `description` field. We apply the description `Unspecified` to all items that either do not have a `description` field of items that have a `null` description.
 
 
 [[mongo.custom-converters]]