DATAMONGO-757 - Align output of projection operation with MongoDB defaults.

Adjusted FieldProjection to generate an appropriate representation of included / excluded fields (namely :1 for included and :0 for excluded).
Polished guards to handle only _id is allowed to be excluded (DATAMONGO-758).

Original pull request: #76.

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

@@ -44,6 +44,8 @@ import com.mongodb.DBObject;
 public class ProjectionOperation implements FieldsExposingAggregationOperation {
 
 	private static final List<Projection> NONE = Collections.emptyList();
+	private static final String EXCLUSION_ERROR = "Exclusion of field %s not allowed. Projections by the mongodb "
+			+ "aggregation framework only support the exclusion of the %s field!";
 
 	private final List<Projection> projections;
 
@@ -60,7 +62,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 	 * @param fields must not be {@literal null}.
 	 */
 	public ProjectionOperation(Fields fields) {
-		this(NONE, ProjectionOperationBuilder.FieldProjection.from(fields, true));
+		this(NONE, ProjectionOperationBuilder.FieldProjection.from(fields));
 	}
 
 	/**
@@ -117,23 +119,29 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 	/**
 	 * Excludes the given fields from the projection.
 	 * 
-	 * @param fields must not be {@literal null}.
+	 * @param fieldNames must not be {@literal null}.
 	 * @return
 	 */
-	public ProjectionOperation andExclude(String... fields) {
+	public ProjectionOperation andExclude(String... fieldNames) {
-		List<FieldProjection> excludeProjections = FieldProjection.from(Fields.fields(fields), false);
+
+		for (String fieldName : fieldNames) {
+			Assert.isTrue(Fields.UNDERSCORE_ID.equals(fieldName),
+					String.format(EXCLUSION_ERROR, fieldName, Fields.UNDERSCORE_ID));
+		}
+
+		List<FieldProjection> excludeProjections = FieldProjection.from(Fields.fields(fieldNames), false);
 		return new ProjectionOperation(this.projections, excludeProjections);
 	}
 
 	/**
 	 * Includes the given fields into the projection.
 	 * 
-	 * @param fields must not be {@literal null}.
+	 * @param fieldNames must not be {@literal null}.
 	 * @return
 	 */
-	public ProjectionOperation andInclude(String... fields) {
+	public ProjectionOperation andInclude(String... fieldNames) {
 
-		List<FieldProjection> projections = FieldProjection.from(Fields.fields(fields), true);
+		List<FieldProjection> projections = FieldProjection.from(Fields.fields(fieldNames), true);
 		return new ProjectionOperation(this.projections, projections);
 	}
 
@@ -387,31 +395,31 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 				this.value = value;
 			}
 
+			/**
+			 * Factory method to easily create {@link FieldProjection}s for the given {@link Fields}. Fields are projected as
+			 * references with their given name. A field {@code foo} will be projected as: {@code foo : 1 } .
+			 * 
+			 * @param fields the {@link Fields} to in- or exclude, must not be {@literal null}.
+			 * @return
+			 */
+			public static List<? extends Projection> from(Fields fields) {
+				return from(fields, null);
+			}
+
 			/**
 			 * Factory method to easily create {@link FieldProjection}s for the given {@link Fields}.
 			 * 
 			 * @param fields the {@link Fields} to in- or exclude, must not be {@literal null}.
-			 * @param include whether to include or exclude the fields.
+			 * @param value to use for the given field.
 			 * @return
 			 */
-			public static List<FieldProjection> from(Fields fields, boolean include) {
+			public static List<FieldProjection> from(Fields fields, Object value) {
 
 				Assert.notNull(fields, "Fields must not be null!");
 				List<FieldProjection> projections = new ArrayList<FieldProjection>();
 
 				for (Field field : fields) {
-
+					projections.add(new FieldProjection(field, value));
-					if (!include) {
-						if (!Fields.UNDERSCORE_ID.equals(field.getName())) {
-							throw new IllegalArgumentException(
-									String
-											.format(
-													"Exclusion of field %s not allowed. Projections by the mongodb aggregation framework only support the exclusion of the %s field!",
-													field.getName(), Fields.UNDERSCORE_ID));
-						}
-					}
-
-					projections.add(new FieldProjection(field, include ? null : 0));
 				}
 
 				return projections;
@@ -423,13 +431,32 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 			 */
 			@Override
 			public DBObject toDBObject(AggregationOperationContext context) {
+				return new BasicDBObject(field.getName(), renderFieldValue(context));
+			}
 
-				if (value != null) {
+			private Object renderFieldValue(AggregationOperationContext context) {
-					return new BasicDBObject(field.getName(), value);
+
+				// implicit reference or explicit include?
+				if (value == null || Boolean.TRUE.equals(value)) {
+
+					// check whether referenced field exists in the context
+					FieldReference reference = context.getReference(field.getTarget());
+
+					if (field.getName().equals(field.getTarget())) {
+
+						// render field as included
+						return 1;
+					}
+
+					// render field reference
+					return reference.toString();
+				} else if (Boolean.FALSE.equals(value)) {
+
+					// render field as excluded
+					return 0;
 				}
 
-				FieldReference reference = context.getReference(field.getTarget());
+				return value;
-				return new BasicDBObject(field.getName(), reference.toString());
 			}
 		}
 

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

@@ -66,7 +66,7 @@ public class ProjectionOperationUnitTests {
 		DBObject dbObject = operation.toDBObject(Aggregation.DEFAULT_CONTEXT);
 		DBObject projectClause = DBObjectUtils.getAsDBObject(dbObject, PROJECT);
 
-		assertThat(projectClause.get("foo"), is((Object) "$foo"));
+		assertThat((Integer) projectClause.get("foo"), is(1));
 		assertThat(projectClause.get("bar"), is((Object) "$foobar"));
 	}
 
@@ -197,7 +197,7 @@ public class ProjectionOperationUnitTests {
 	 * @see DATAMONGO-758
 	 */
 	@Test
-	public void excludeShouldExclusionOfUnderscoreId() {
+	public void excludeShouldAllowExclusionOfUnderscoreId() {
 
 		ProjectionOperation projectionOp = new ProjectionOperation().andExclude(Fields.UNDERSCORE_ID);
 		DBObject dbObject = projectionOp.toDBObject(Aggregation.DEFAULT_CONTEXT);
@@ -205,6 +205,25 @@ public class ProjectionOperationUnitTests {
 		assertThat((Integer) projectClause.get(Fields.UNDERSCORE_ID), is(0));
 	}
 
+	/**
+	 * @see DATAMONGO-757
+	 */
+	@Test
+	public void usesImplictAndExplicitFieldAliasAndIncludeExclude() {
+
+		ProjectionOperation operation = Aggregation.project("foo").and("foobar").as("bar").andInclude("inc1", "inc2")
+				.andExclude("_id");
+
+		DBObject dbObject = operation.toDBObject(Aggregation.DEFAULT_CONTEXT);
+		DBObject projectClause = DBObjectUtils.getAsDBObject(dbObject, PROJECT);
+
+		assertThat(projectClause.get("foo"), is((Object) 1)); // implicit
+		assertThat(projectClause.get("bar"), is((Object) "$foobar")); // explicit
+		assertThat(projectClause.get("inc1"), is((Object) 1)); // include shortcut
+		assertThat(projectClause.get("inc2"), is((Object) 1));
+		assertThat(projectClause.get("_id"), is((Object) 0));
+	}
+
 	@Test(expected = IllegalArgumentException.class)
 	public void arithmenticProjectionOperationModByZeroException() {