mongodb 查询问题。

{class:“技术类” title=“xxxxxx” content:“xxxxxx” } {class:“招聘类” title=“xxxxxx” content:“xxxxxx” } {class:“分享类” title=“xxxxxx” content:“xxxxxx” } {class:“分享类” title=“xxxxxx” content:“xxxxxx” } {class:“招聘类” title=“xxxxxx” content:“xxxxxx” }

我怎么通过查询一次性取出结果是:

[ {class:“技术类”}, {class:“招聘类”}, {class:“分享类”}]