$elemmatch只返回一个结果[duplicate]

假设我的收藏中有以下文档:

{  
   "_id":ObjectId("562e7c594c12942f08fe4192"),
   "shapes":[  
      {  
         "shape":"square",
         "color":"blue"
      },
      {  
         "shape":"circle",
         "color":"red"
      }
   ]
},
{  
   "_id":ObjectId("562e7c594c12942f08fe4193"),
   "shapes":[  
      {  
         "shape":"square",
         "color":"black"
      },
      {  
         "shape":"circle",
         "color":"green"
      }
   ]
}

执行查询:

db.test.find({"shapes.color": "red"}, {"shapes.color": 1})

db.test.find({shapes: {"$elemMatch": {color: "red"}}}, {"shapes.color": 1})

返回匹配的文档 ,但始终包含所有数组项 shapes :

{ "shapes": 
  [
    {"shape": "square", "color": "blue"},
    {"shape": "circle", "color": "red"}
  ] 
}

不过,我想拿到文件 (文件1) 只包含 color=red :

{ "shapes": 
  [
    {"shape": "circle", "color": "red"}
  ] 
}

我该怎么做?