需要细微调整才能完成工作，以下是查询:

A minor tweak does the job, below is the query :

user1 = list(community.aggregate([{
    "$match": { "_id": ObjectId("5dc1f30abcafe70001bd0075") }
},
{
    "$lookup": {
        "from": "profile",
        "localField": "user_id",
        "foreignField": "_id",
        "as": "details"
    }
}, { "$unwind": "$details" }, { "$match": { "details.username": /eesh/i } }, {
    "$project": {
        "_id": 0,
        "username": "$details.username",
        "name": "$details.name"
    }
}]))

请根据您的要求动态传递/eesh/i.换句话说，我尝试在$lookup本身中添加此过滤器{ "details.username": /eesh/i }-这样我们就可以避免遵循$unwind& $match阶段，但是由于要检查两个过滤器-由于$match的$expr中使用regex的限制很少，因此此查询为&甚至更容易做到.

Please pass /eesh/i dynamically as per your requirement. In the other way I've tried to add this filter { "details.username": /eesh/i } in $lookup itself - that way we can avoid following $unwind & $match stages, But as we've two filters to be checked - due to few limitations on using regex in $expr of $match, this query is the one & even this is easier to do.