仅在mongodb聚合中返回带有最新子文档的文档

您可以使用

$unwind

$sort

$group

Thread.aggregate([    // Duplicate the docs, one per messages element.    {$unwind: '$messages'},     // Sort the pipeline to bring the most recent message to the front    {$sort: {'messages.date_added': -1}},     // Group by _id+title, taking the first (most recent) message per group    {$group: {        _id: { _id: '$_id', title: '$title' },         message: {$first: '$messages'}    }},    // Reshape the document back into the original style    {$project: {_id: '$_id._id', title: '$_id.title', message: 1}}]);