mongodb中的嵌套查询

Question

如何在mongoDB 2或3中查询以下文档中的所有标签:

{
    "_id" : ObjectId("55dc45017137a4e70b8b4569"),
    "campainName" : "",
    "themeName" : "theme1",
    "emailListName" : "eiEmails",
    "emailSubject" : "",
    "emailFrom" : "",
    "allNews" : [ 
        {
            "type" : "1",
            "tag" : ['aa','bb','cc'],
            "link" : "",
            "image" : ""
        }
    ]
},
{
    "_id" : ObjectId("55dc45017137a4e70b8b4570"),
    "campainName" : "",
    "themeName" : "theme2",
    "emailListName" : "afaeiEmails",
    "emailSubject" : "",
    "emailFrom" : "",
    "allNews" : [ 
        {
            "type" : "1",
            "tag" : ['da','db','dc'],
            "link" : "",
            "image" : ""
        }
    ]
}

我需要这样的结果:

{['aa','bb','cc'], ['da','db','dc']}

我需要在doctrine odm中的查询样式。

Answer 1

试试这样:

db.collection.find({}, {"allNews.tag" : 1, _id : 0})