在mongodb中更新子文档？

Question

如何定位authors数组中的子文档，如下所示，以便更新它？

collection.update({'_id': "4f44af6a024342300e000001"}, {$set: { 'authors.?' }} )

文件：

{
    _id:     "4f44af6a024342300e000001",
    title:   "A book", 
    created: "2012-02-22T14:12:51.305Z"
    authors: [{"_id":"4f44af6a024342300e000002"}] 
}

Answer 1

通过指定嵌入文档的实际位置，如下所示：

// update _id field of first author    
collection.update({'_id': "4f44af6a024342300e000001"}, 
                  {$set: { 'authors.0._id': "1" }} )

或通过positional operator：

// update _id field of first matched by _id author    
collection.update({'_id': "4f44af6a024342300e000001",
                    //you should specify query for embedded document
                    'authors._id' : "4f44af6a024342300e000002" }, 
     // you can update only one nested document matched by query                   
                    {$set: { 'authors.$._id': "1" }} )