父属性上的Mongodb聚合筛选器查找

给定这样一个对象，如果

isAnonymous

字段为

false

，我如何使其成为lookup users info

{ 
"_id" : ObjectId(""), 
"user" : ObjectId(""), 
"title" : "This is an idea", 
"shortDescription" : "Pretty cool stuff",
"downVoteCount" : NumberInt(0), 
"upVoteCount" : NumberInt(12), 
"voteTotalCount" : NumberInt(12), 
"deleted" : false, 
"ideaNumber" : NumberInt(5),
"isAnonymous" : false, 
"created" : ISODate("2018-01-19T23:37:10.949+0000")
}

以下是我当前的查询：

db.ideas.aggregate(
{
    $match: { "deleted": false }
},
{
    $lookup: {
        "from" : "users",
        "localField" : "user",
        "foreignField" : "_id",
        "as" : "user"
    }
},
{
    $unwind: {
        path : "$user",
        includeArrayIndex : "arrayIndex", // optional
        preserveNullAndEmptyArrays : false // optional
    }
},
{
    $project: {
        "ideaNumber": 1,
        "title": 1,
        "isAnonymous": 1,
        "shortDescription": 1,
        "upVoteCount": 1,
        "created": 1,
        "user.email": 1,
        "user.name": 1,
        "user.createdAt": 1
    }
},
);

生成如下对象：

{ 
"_id" : ObjectId(""), 
"user" : {
    "createdAt" : ISODate("2018-01-19T21:50:02.758+0000"), 
    "email" : "blah", 
    "name" : "Foo Bar"
}, 
"title" : "This is an idea", 
"shortDescription" : "Pretty cool stuff", 
"upVoteCount" : NumberInt(12), 
"ideaNumber" : NumberInt(5), 
"isAnonymous" : false, 
"created" : ISODate("2018-01-19T23:37:10.949+0000")

}

我想看看像这样的物体

{ 
"_id" : ObjectId(""), 
"user" : {
    "createdAt" : "anonymous", 
    "email" : "anonymous", 
    "name" : "anonymous"
}, 
"title" : "This is an idea", 
"shortDescription" : "Pretty cool stuff", 
"upVoteCount" : NumberInt(12), 
"ideaNumber" : NumberInt(5), 
"isAnonymous" : false, 
"created" : ISODate("2018-01-19T23:37:10.949+0000")
}

---

可以对投影字段使用$cond语句：

db.ideas.aggregate(
    {
        $match: { "deleted": false }
    },
    {
        $lookup: {
            "from": "users",
            "localField": "user",
            "foreignField": "_id",
            "as": "user"
        }
    },
    {
        $unwind: {
            path: "$user",
            includeArrayIndex: "arrayIndex", // optional
            preserveNullAndEmptyArrays: false // optional
        }
    },
    {
        $project: {
            "ideaNumber": 1,
            "title": 1,
            "isAnonymous": 1,
            "shortDescription": 1,
            "upVoteCount": 1,
            "created": 1,
            "user.email": {
                $cond: {
                    if: { $eq: ["$isAnonymous", true] },
                    then: "anonymous",
                    else: "$user.email"
                }
            },
            "user.name": 1,
            "user.createdAt": 1
        }
    },
);

当然，您应该将其应用于其他两个字段。如果您甚至不想向他们显示结果，请在最后一个阶段使用筛选器$match

{
    $match: { isAnonymous: { $ne: "anonymous" } }
} 

---

可以对投影字段使用$cond语句：

db.ideas.aggregate(
    {
        $match: { "deleted": false }
    },
    {
        $lookup: {
            "from": "users",
            "localField": "user",
            "foreignField": "_id",
            "as": "user"
        }
    },
    {
        $unwind: {
            path: "$user",
            includeArrayIndex: "arrayIndex", // optional
            preserveNullAndEmptyArrays: false // optional
        }
    },
    {
        $project: {
            "ideaNumber": 1,
            "title": 1,
            "isAnonymous": 1,
            "shortDescription": 1,
            "upVoteCount": 1,
            "created": 1,
            "user.email": {
                $cond: {
                    if: { $eq: ["$isAnonymous", true] },
                    then: "anonymous",
                    else: "$user.email"
                }
            },
            "user.name": 1,
            "user.createdAt": 1
        }
    },
);

当然，您应该将其应用于其他两个字段。如果您甚至不想向他们显示结果，请在最后一个阶段使用筛选器$match

{
    $match: { isAnonymous: { $ne: "anonymous" } }
} 

---

实际上，您可以在聚合管道中使用条件来更改投影

以下查询应以所需格式投影

db.T.aggregate([
{
    $match: { "deleted": false }
},
{
    $lookup: {
        "from" : "users",
        "localField" : "user",
        "foreignField" : "_id",
        "as" : "user"
    }
},
{
    $unwind: {
        path : "$user",
        includeArrayIndex : "arrayIndex", // optional
        preserveNullAndEmptyArrays : false // optional
    }
},
{ 
    $project:{
        "ideaNumber": 1,
        "title": 1,
        "isAnonymous": 1,
        "shortDescription": 1,
        "upVoteCount": 1,
        "created": 1,
         user : {$cond: [{$eq:["$isAnonymous", true]}, 
         {
            "createdAt" : "anonymous", 
            "email" : "anonymous", 
            "name" : "anonymous"
         }, 
         {
            "createdAt" : "$user.createdAt", 
            "email" : "$user.email", 
            "name" : "$user.name"
         }]}
    }
}]);

上述查询导致的结果如下：

{ 
    "_id" : ObjectId("5a876fae304c013cbf854766"), 
    "title" : "This is an idea", 
    "shortDescription" : "Pretty cool stuff", 
    "upVoteCount" : NumberInt(12), 
    "ideaNumber" : NumberInt(5), 
    "isAnonymous" : false, 
    "created" : ISODate("2018-01-19T23:37:10.949+0000"), 
    "user" : {
        "createdAt" : ISODate("2018-01-19T23:37:10.949+0000"), 
        "email" : "abc@cde.com", 
        "name" : "user A"
    }
}

---

实际上，您可以在聚合管道中使用条件来更改投影

以下查询应以所需格式投影

db.T.aggregate([
{
    $match: { "deleted": false }
},
{
    $lookup: {
        "from" : "users",
        "localField" : "user",
        "foreignField" : "_id",
        "as" : "user"
    }
},
{
    $unwind: {
        path : "$user",
        includeArrayIndex : "arrayIndex", // optional
        preserveNullAndEmptyArrays : false // optional
    }
},
{ 
    $project:{
        "ideaNumber": 1,
        "title": 1,
        "isAnonymous": 1,
        "shortDescription": 1,
        "upVoteCount": 1,
        "created": 1,
         user : {$cond: [{$eq:["$isAnonymous", true]}, 
         {
            "createdAt" : "anonymous", 
            "email" : "anonymous", 
            "name" : "anonymous"
         }, 
         {
            "createdAt" : "$user.createdAt", 
            "email" : "$user.email", 
            "name" : "$user.name"
         }]}
    }
}]);

上述查询导致的结果如下：

{ 
    "_id" : ObjectId("5a876fae304c013cbf854766"), 
    "title" : "This is an idea", 
    "shortDescription" : "Pretty cool stuff", 
    "upVoteCount" : NumberInt(12), 
    "ideaNumber" : NumberInt(5), 
    "isAnonymous" : false, 
    "created" : ISODate("2018-01-19T23:37:10.949+0000"), 
    "user" : {
        "createdAt" : ISODate("2018-01-19T23:37:10.949+0000"), 
        "email" : "abc@cde.com", 
        "name" : "user A"
    }
}

---

所以当anonymous为false时，您需要用户信息否？只是想看看问题出在哪里。顺便说一句，如果您正在寻找条件查找，则不可能。@Veeram条件查找在v3.6中可用，我对此版本没有经验，但您可以在文档中找到它：@Veeram确实可以在mongodb中进行条件查找。@RaulRueda这怎么可能？我认为应该有一个表达式来决定是否应该执行查找。你们能给我举个例子吗？3.6是基于多个条件的连接。条件$lookup与在后续阶段（如$projection或$match）中应用过滤器完全不同。请阅读我发布的链接，其中有很多关于它们如何工作以及它们具有哪些属性的示例。因此，当anonymous为false时，您需要用户信息否？只是想看看问题出在哪里。顺便说一句，如果您正在寻找条件查找，则不可能。@Veeram条件查找在v3.6中可用，我对此版本没有经验，但您可以在文档中找到它：@Veeram确实可以在mongodb中进行条件查找。@RaulRueda这怎么可能？我认为应该有一个表达式来决定是否应该执行查找。你们能给我举个例子吗？3.6是基于多个条件的连接。条件$lookup与在后续阶段（如$projection或$match）中应用过滤器完全不同。请阅读我发布的链接，其中有很多关于它们如何工作以及它们具有哪些属性的示例。