更新mongodb中的子文檔？

Question

如何爲authors陣列定位子文檔，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

通過指定這樣的嵌入文檔的實際位置：

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

或通過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" }})