我有一个集合,其中包含两种类型的文档。根据我要执行查找聚合的文档类型。
Action 是一个集合,其中包含对话和消息类型的操作。我想根据 MongoDB 中存在的字段以不同方式查找对话和消息。
对话类型的 Action 文档如下
{
"_id" : ObjectId("592bdeaf45c7201421793871"),
"actionType" : "conversation",
"created" : NumberInt(1496047280),
"users" : [
ObjectId("590c53a85fba594a59fe3d0f"),
ObjectId("590c50175df715499129e41b")
],
"conversationId" : ObjectId("592bdeaf45c7201421793870"),
"missionId" : ObjectId("590c50fa5df715499129e41c")
}
消息的操作文档
{
"_id" : ObjectId("592bdeaf45c7201421793871"),
"actionType" : "message",
"created" : NumberInt(1496047280),
"messageId" : ObjectId("592bdeaf45c7201421793870")
}
我希望在特定时间后执行操作,并希望执行查找以从其对象 ID 中获取对话和消息数据。
我试过了
let matchQuery = {
users : new ObjectId(userId),
created:
{
$gt : createdTime
}};
let aggregation = [
{
$match : matchQuery
},
{$cond :
{if:
{
$users:{
$exists:true
}
},
then: {
$unwind : "$users",
$lookup: {
from : "users",
localfield:"$users",
foreignfield:"_id",
as:"userDetail"
},
$group:{
"users" : { $push : "userDetail"}
}
}
}
},
{$cond :
{if:
{
$conversationId:{
$exists:true
}
},
then: {
$lookup : {
from:"conversations",
localfield:"conversationId",
foreignfield:"_id",
as:"conversationDetail"
}
}
}
},
{$cond :
{if:
{
$missionId:{
$exists:true
}
},
then: {
$lookup : {
from:"services_v2",
localfield:"missionId",
foreignfield:"_id",
as:"missionDetail"
}
}
}
},
{$cond :
{if:
{
$messageId:{
$exists:true
}
},
then: {
$lookup : {
from:"messagev2",
localfield:"messageId",
foreignfield:"_id",
as:"messageDetail"
}
}
}
},
{
$project : {
"_id" : 1,
"actionType" : 1,
"userDetail":1,
"conversationDetail":1,
"missionDetail":1,
"messageDetail":1
}}
];
connection.collection('actions')
.aggregate(aggregation).toArray((err,result)=> {
if(err){
console.log(err);
}
console.log(result);
})
};
最佳答案
我认为您对此有点想多了,您不需要“条件查找”,最好通过示例来演示。
将这些文档放在单独的集合中,首先是对话:
> db.conversation.find()
{ "_id" : ObjectId("592ccbf8fceb6b40e6489759"), "message" : "I'm here" }
然后是消息集合:
> db.message.find()
{ "_id" : ObjectId("592ccc0bfceb6b40e648975a"), "text" : "Something here" }
然后我有一个主集合,其中包含对单独文档中每个文档的引用:
> db.master.find()
{
"_id" : ObjectId("592ccc73fceb6b40e648975b"),
"a" : 1,
"conversation" : ObjectId("592ccbf8fceb6b40e6489759")
}
{
"_id" : ObjectId("592ccc95fceb6b40e648975c"),
"a" : 2,
"message" : ObjectId("592ccc0bfceb6b40e648975a")
}
现在,如果我执行 $lookup
操作(有点类似于“左连接”):
db.master.aggregate([
{ "$lookup": {
"from": "conversation",
"localField": "conversation",
"foreignField": "_id",
"as": "conversation"
}}
])
然后我得到这样的结果,它当然会在文档上投影一个没有 "localField"
匹配的空数组:
{
"_id" : ObjectId("592ccc73fceb6b40e648975b"),
"a" : 1,
"conversation" : [
{
"_id" : ObjectId("592ccbf8fceb6b40e6489759"),
"message" : "I'm here"
}
]
}
{
"_id" : ObjectId("592ccc95fceb6b40e648975c"),
"a" : 2,
"message" : ObjectId("592ccc0bfceb6b40e648975a"),
"conversation" : [ ]
}
如果我现在向管道添加“第二个”$lookup
链接到消息集合的操作:
db.master.aggregate([
{ "$lookup": {
"from": "conversation",
"localField": "conversation",
"foreignField": "_id",
"as": "conversation"
}},
{ "$lookup": {
"from": "message",
"localField": "message",
"foreignField": "_id",
"as": "message"
}}
])
然后我们看到类似的效果,没有属性的文档现在有一个空数组,但是在确实存在属性的地方,我们现在有了来自特定集合的条目:
{
"_id" : ObjectId("592ccc73fceb6b40e648975b"),
"a" : 1,
"conversation" : [
{
"_id" : ObjectId("592ccbf8fceb6b40e6489759"),
"message" : "I'm here"
}
],
"message" : [ ]
}
{
"_id" : ObjectId("592ccc95fceb6b40e648975c"),
"a" : 2,
"message" : [
{
"_id" : ObjectId("592ccc0bfceb6b40e648975a"),
"text" : "Something here"
}
],
"conversation" : [ ]
}
您可以保持原样(这似乎是您迄今为止所尝试的理想最终状态),或者现在对它进行其他操作,例如组合成一个数组:
db.master.aggregate([
{ "$lookup": {
"from": "conversation",
"localField": "conversation",
"foreignField": "_id",
"as": "conversation"
}},
{ "$lookup": {
"from": "message",
"localField": "message",
"foreignField": "_id",
"as": "message"
}},
{ "$project": {
"a": 1,
"combined": {
"$concatArrays": [
{ "$map": {
"input": "$conversation",
"as": "el",
"in": {
"type": "conversation",
"_id": "$$el._id",
"message": "$$el.message"
}
}},
{ "$map": {
"input": "$message",
"as": "el",
"in": {
"type": "message",
"_id": "$$el._id",
"text": "$$el.text"
}
}}
]
}
}}
])
输出如下:
{
"_id" : ObjectId("592ccc73fceb6b40e648975b"),
"a" : 1,
"combined" : [
{
"type" : "conversation",
"_id" : ObjectId("592ccbf8fceb6b40e6489759"),
"message" : "I'm here"
}
]
}
{
"_id" : ObjectId("592ccc95fceb6b40e648975c"),
"a" : 2,
"combined" : [
{
"type" : "message",
"_id" : ObjectId("592ccc0bfceb6b40e648975a"),
"text" : "Something here"
}
]
}
关键是$lookup
如果 "localField"
或 "foreignField"
表达式不匹配任何元素,则会故意简单地留下一个“空数组”。除了为目标添加空数组属性外,这不会影响返回的文档结果。
现在您可以使用 $unwind
“松散”文档, 但只有在省略 "preserveNullAndEmptyArrays"
时才会发生这种情况选项,用于处理此类事件。
但是对于基于“鉴别器”的一般用法$lookup
,然后只需为要“链接”到的每个集合使用单独的管道阶段。
关于mongodb - 仅当本地字段存在时才执行条件查找?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/44241188/