mongo数组查询，如何仅返回当前匹配数组？

Question

db.test.find();
{
_id:ObjectId('55e99a2190df7a911d6ed1f1'),
list:[
{
"aa":10,
"data":"test"
},
{
"aa":1,
"data":"test"
}
]
}
db.test.find({_id:ObjectId('55e99a2190df7a911d6ed1f1'),list:{'$elemMatch':{'aa':1}}})
预期结果：
{_id:ObjectId('55e99a2190df7a911d6ed1f1'),
list:{
"aa":1,
"data":"test"
}

Answer 1

>db.customer.find().pretty(){"_id":ObjectId("559bb1d1d39f0dcac2658f8e"),"cust_id":"abc123","ord_date":ISODate("2012-10-03T16:00:00Z"),"status":"A","price":25,"items":[{"sku":"mmm","qty":5,"price":2.5},{"sku":"nnn","qty":5,"price":2.5}]}{"_id":ObjectId("559bb1ead39f0dcac2658f8f"),"cust_id":"abc123","ord_date":ISODate("2012-10-03T16:00:00Z"),"status":"B","price":30,"items":[{"sku":"mmm","qty":6,"price":3.5},{"sku":"nnn","qty":6,"price":3.5}]}{"_id":ObjectId("559bb200d39f0dcac2658f90"),"cust_id":"abc123","ord_date":ISODate("2012-10-03T16:00:00Z"),"status":"C","price":35,"items":[{"sku":"mmm","qty":7,"price":4.5},{"sku":"nnn","qty":7,"price":4.5}]}>db.customer.find({"items.qty":6},{"items.$":1}).pretty()//只返回和查询条件匹配的那一个元素{"_id":ObjectId("559bb1ead39f0dcac2658f8f"),"items":[{"sku":"mmm","qty":6,"price":3.5}]}查询匹配的内嵌文档，你也可以直接查询，如：>db.customer.find({"items.qty":6}).pretty(){"_id":ObjectId("559bb1ead39f0dcac2658f8f"),"cust_id":"abc123","ord_date":ISODate("2012-10-03T16:00:00Z"),"status":"B","price":30,"items":[{"sku":"mmm","qty":6,"price":3.5},{"sku":"nnn","qty":6,"price":3.5}]}对应你上面的查询实现：>db.customer.find({"_id":ObjectId("559bb1ead39f0dcac2658f8f"),items:{'$elemMatch':{'sku':"mmm"}}},{"items.$":1}).pretty(){"_id":ObjectId("559bb1ead39f0dcac2658f8f"),"items":[{"sku":"mmm","qty":6,"price":3.5}]}db.test.find({_id:ObjectId('55e99a2190df7a911d6ed1f1'),list:{'$elemMatch':{'aa':1}}},{"list.$":1}).pretty()