MongoDB query with conditional group by statement

问题

I need to export customer records from database of mongoDB. Exported customer records should not have duplicated values. "firstName+lastName+code" is the key to DE-duped the record and If there are two records present in database with same key then I need to give preference to source field with value other than email.

customer (id,firstName,lastName,code,source) collection is this.

If there are record 3 records with same unique key and 3 different sources then i need to choose only one record between 2 sources(TV,internet){or if there are n number of sources i need the one record only}not with the 'email'(as email will be choosen when only one record is present with the unique key and source is email) query using:

`db.customer.aggregate([
 { "$match" : { "active" : true , "dealerCode" : { "$in" : [ "111391"]} , "source" : { "$in" : [ "email","TV","internet"]}}},
   {$group:{"_id":{
                  "firstName":"$personalInfo.firstName",
                  "lastName":"$personalInfo.lastName",
                  "code":"$vehicle.code"},              
        "source":{
                   $addToSet:{"source":"$source"}
                 }
        }
    },
    {$redact: 
        {$cond:[{$eq:[{$ifNull:["$source","other"]},"email"]},"$$PRUNE","$$DESCEND"]}
    },
   {$project:
        {"source":
            {$map:
                  {"input":
                       {$cond:[
                         {$eq:[{$size:"$source"},0]},[{"source":"email"}],"$source"]
                        },"as":"inp","in":"$$inp.source"}
            },
            "record":{"_id":1}
        }
    } ])`

sample output: { "_id" : { "firstName" : "sGI6YaJ36WRfI4xuJQzI7A==", "lastName" : "99eQ7i+uTOqO8X+IPW+NOA==", "code" : "1GTHK23688F113955" }, "source" : [ "internet" ] } { "_id" : { "firstName" : "WYDROTF/9vs9O7XhdIKd5Q==", "lastName" : "BM18Uq/ltcbdx0UJOXh7Sw==", "code" : "1G4GE5GV5AF180133" }, "source" : [ "internet" ] } { "_id" : { "firstName" : "id+U2gYNHQaNQRWXpe34MA==", "lastName" : "AIs1G33QnH9RB0nupJEvjw==", "code" : "1G4GE5EV0AF177966" }, "source" : [ "internet" ] } { "_id" : { "firstName" : "qhreJVuUA5l8lnBPVhMAdw==", "lastName" : "petb0Qx3YPfebSioY0wL9w==", "code" : "1G1AL55F277253143" }, "source" : [ "TV" ] } { "_id" : { "firstName" : "qhreJVuUA5l8lnBPVhMAdw==", "lastName" : "6LB/NmhbfqTagbOnHFGoog==", "code" : "1GCVKREC0EZ168134" }, "source" : [ "TV", "internet" ] }

This is a problem with this query please suggest :(

回答1:

Your code doesn't work, because $cond is not an accumulator operator. Only these accumulator operators, can be used in a $group stage.

Assuming your records contain not more than two possible values of source as you mention in your question, you could add a conditional $project stage and modify the $group stage as,

Code:

db.customer.aggregate([
{$group:{"_id":{"id":"$id",
                "firstName":"$firstName",
                "lastName":"$lastName",
                "code":"$code"},
         "sourceA":{$first:"$source"},
         "sourceB":{$last:"$source"}}},
{$project:{"source":{$cond:[{$eq:["$sourceA","email"]},
                            "$sourceB",
                            "$sourceA"]}}}
])

In case there can be more that two possible values for source, then you could do the following:

• Group by the id, firstName, lastName and code. Accumulate the unique values of source, using the $addToSet operator.
• Use $redact to keep only the values other than email.
• Project the required fields, if the source array is empty(all the elements have been removed), add a value email to it.
• Unwind the source field to list it as a field and not an array. (optional)

Code:

db.customer.aggregate([
{$group:{"_id":{"id":"$id",
                "firstName":"$firstName",
                "lastName":"$lastName",
                "code":"$code"},
         "sourceArr":{$addToSet:{"source":"$source"}}}},
{$redact:{$cond:[{$eq:[{$ifNull:["$source","other"]},"email"]},
          "$$PRUNE",
          "$$DESCEND"]}},
{$project:{"source":{$map:{"input":
                           {$cond:[{$eq:[{$size:"$sourceArr"},
                                         0]},
                                   [{"source":"item"}],
                                   "$sourceArr"]},
                           "as":"inp",
                           "in":"$$inp.source"}}}}
])

来源：https://stackoverflow.com/questions/28191069/mongodb-query-with-conditional-group-by-statement