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Calculate average of ratings in array and then include the field to original document in MongoDB?
You can use $avg operator along with aggregate framework. Let us first create a collection with documents −
> db.averageOfRatingsInArrayDemo.insertOne(
... {
... "StudentDetails":[
... {
... "StudentId":1,
... "StudentScore":45
... },
... {
... "StudentId":2,
... "StudentScore":58
... },
... {
... "StudentId":3,
... "StudentScore":67
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd427dc2cba06f46efe9ee4")
}Following is the query to display all documents from a collection with the help of find() method −
> db.averageOfRatingsInArrayDemo.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5cd427dc2cba06f46efe9ee4"),
"StudentDetails" : [
{
"StudentId" : 1,
"StudentScore" : 45
},
{
"StudentId" : 2,
"StudentScore" : 58
},
{
"StudentId" : 3,
"StudentScore" : 67
}
]
}Following is the query to calculate average of ratings in array and then include field to original document in MongoDB −
> db.averageOfRatingsInArrayDemo.aggregate([ {$addFields : {StudentScoreAverage : {$avg : "$StudentDetails.StudentScore"}}} ]);This will produce the following output −
{ "_id" : ObjectId("5cd427dc2cba06f46efe9ee4"), "StudentDetails" : [ { "StudentId" : 1, "StudentScore" : 45 }, { "StudentId" : 2, "StudentScore" : 58 }, { "StudentId" : 3, "StudentScore" : 67 } ], "StudentScoreAverage" : 56.666666666666664 }
Updated on: 30-Jul-2019
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