merge #1150

closes #1150
MorphiaOrg · Jan 19, 2019 · e55e609 · e55e609
1 parent 9d3a592
commit e55e609
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Showing 3 changed files with 53 additions and 4 deletions.
diff --git a/morphia/src/main/java/xyz/morphia/aggregation/AggregationPipelineImpl.java b/morphia/src/main/java/xyz/morphia/aggregation/AggregationPipelineImpl.java
@@ -242,7 +242,6 @@ public AggregationPipeline unwind(final String field, final UnwindOptions option
      * @param projection the project to apply
      * @return the DBObject
      */
-    @SuppressWarnings("unchecked")
     private DBObject toDBObject(final Projection projection) {
         String target;
         if (firstStage) {
@@ -262,10 +261,22 @@ private DBObject toDBObject(final Projection projection) {
         } else if (projection.getSource() != null) {
             return new BasicDBObject(target, projection.getSource());
         } else if (projection.getArguments() != null) {
+            DBObject args = toExpressionArgs(projection.getArguments());
             if (target == null) {
-                return toExpressionArgs(projection.getArguments());
+                // Unwrap for single-argument expressions
+                if (args instanceof List<?> && ((List<?>) args).size() == 1) {
+                    Object firstArg = ((List<?>) args).get(0);
+                    if (firstArg instanceof DBObject) {
+                        return (DBObject) firstArg;
+                    }
+                }
+                return args;
             } else {
-                return new BasicDBObject(target, toExpressionArgs(projection.getArguments()));
+                // Unwrap for single-argument expressions
+                if (args instanceof List<?> && ((List<?>) args).size() == 1) {
+                    return new BasicDBObject(target, ((List<?>) args).get(0));
+                }
+                return new BasicDBObject(target, args);
             }
         } else {
             return new BasicDBObject(target, projection.isSuppressed() ? 0 : 1);
@@ -312,7 +323,7 @@ private DBObject toExpressionArgs(final List<Object> args) {
                 result.add(arg);
             }
         }
-        return result.size() == 1 ? (DBObject) result.get(0) : result;
+        return result;
     }
 
     @Override

diff --git a/morphia/src/main/java/xyz/morphia/aggregation/Projection.java b/morphia/src/main/java/xyz/morphia/aggregation/Projection.java
@@ -140,6 +140,17 @@ public static  Projection divide(final Object arg1, final Object arg2) {
         return expression("$divide", arg1, arg2);
     }
 
+    /**
+     * Counts and returns the total the number of items in an array
+     *
+     * @param expression The argument for $size can be any expression as long as it resolves to an array.
+     * @return the projection
+     * @mongodb.driver.manual reference/operator/aggregation/size $size
+     */
+    public static Projection size(final Object expression) {
+        return expression("$size", expression);
+    }
+
     /**
      * Creates a modulo projection
      *

diff --git a/morphia/src/test/java/xyz/morphia/aggregation/AggregationTest.java b/morphia/src/test/java/xyz/morphia/aggregation/AggregationTest.java
@@ -62,6 +62,7 @@
 import static xyz.morphia.aggregation.Projection.divide;
 import static xyz.morphia.aggregation.Projection.expression;
 import static xyz.morphia.aggregation.Projection.projection;
+import static xyz.morphia.aggregation.Projection.size;
 import static xyz.morphia.geo.GeoJson.point;
 import static xyz.morphia.query.Sort.ascending;
 
@@ -410,6 +411,32 @@ public void testProjection() {
 
     }
 
+    @Test
+    public void testSizeProjection() {
+        getDs().save(asList(new Book("The Banquet", "Dante", 2),
+                            new Book("Divine Comedy", "Dante", 1),
+                            new Book("Eclogues", "Dante", 2),
+                            new Book("The Odyssey", "Homer", 10),
+                            new Book("Iliad", "Homer", 10)));
+
+        final AggregationPipeline pipeline = getDs().createAggregation(Book.class)
+                                                    .group("author", grouping("titles", addToSet("title")))
+                                                    .project(projection("_id").suppress(),
+                                                             projection("author", "_id"),
+                                                             projection("copies", size(projection("titles"))))
+                                                    .sort(ascending("author"));
+        Iterator<Book> aggregate = pipeline.aggregate(Book.class);
+        Book book = aggregate.next();
+        Assert.assertEquals("Dante", book.author);
+        Assert.assertEquals(3, book.copies.intValue());
+
+        final List<DBObject> stages = ((AggregationPipelineImpl) pipeline).getStages();
+        Assert.assertEquals(stages.get(0), obj("$group", obj("_id", "$author").append("titles", obj("$addToSet", "$title"))));
+        Assert.assertEquals(stages.get(1), obj("$project", obj("_id", 0)
+            .append("author", "$_id")
+            .append("copies", obj("$size", "$titles"))));
+    }
+
     @Test
     public void testSkip() {
         getDs().save(asList(new Book("The Banquet", "Dante", 2),