MongoDB-তে প্রজেক্ট ফিল্ড ব্যবহার করা

MongoDB-তে ফিল্ড প্রজেক্ট করতে $project ব্যবহার করুন। একটি কালেকশন তৈরি করি:

> db.demo439.insertOne( ...    { ...       "Name" : "Chris", ...       "MarksInformation" : { ...          "Marks1" : 67, ...          "Marks2" :45, ...          "Marks3" : 78 ...       } ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e77833abbc41e36cc3caeab") } > db.demo439.insertOne( ...    { ...       "Name" : "David", ...       "MarksInformation" : { ...          "Marks1" : 50, ...          "Marks2" :57, ...          "Marks3" : 68 ...       } ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e77833abbc41e36cc3caeac") } > db.demo439.insertOne( ...    { ...       "Name" : "Bob", ...       "MarksInformation" : { ...          "Score1" : 65, ...          "Score2" :71, ... ...       } ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e77833bbbc41e36cc3caead") }

find() মেথড দিয়ে সব ডকুমেন্ট দেখান:

> db.demo439.find();

আউটপুট:

{ "_id" : ObjectId("5e77833abbc41e36cc3caeab"), "Name" : "Chris", "MarksInformation" : { "Marks1" : 67, "Marks2" : 45, "Marks3" : 78 } } { "_id" : ObjectId("5e77833abbc41e36cc3caeac"), "Name" : "David", "MarksInformation" : { "Marks1" : 50, "Marks2" : 57, "Marks3" : 68 } } { "_id" : ObjectId("5e77833bbbc41e36cc3caead"), "Name" : "Bob", "MarksInformation" : { "Score1" : 65, "Score2" : 71 } }

ফিল্ড প্রজেক্ট করার কোয়ারি:

> db.demo439.aggregate({ ...    $project: { ...       "Name" : 1, ...       "Marks1": { $cond: [ { $eq:[ { $ifNull: [ "$MarksInformation.Marks1", 0 ] }, 0 ] },{ $ifNull: [ "$MarksInformation.Score1", 0 ] }, "$MarksInformation.Marks1" ] }, ...       "Marks2": { $cond: [ { $eq:[ { $ifNull: [ "$MarksInformation.Marks2", 0 ] }, 0 ] }, { $ifNull: [ "$MarksInformation.Score2", 0 ] }, "$MarksInformation.Marks2" ] }, ...    "Marks3": { $cond: [ { $eq:[ { $ifNull: [ "$MarksInformation.Marks3", 0] }, 0 ] }, { $ifNull: [ "$MarksInformation.Score3", 0 ] }, "$MarksInformation.Marks3" ] } ... }})

আউটপুট:

{ "_id" : ObjectId("5e77833abbc41e36cc3caeab"), "Name" : "Chris", "Marks1" : 67, "Marks2" : 45, "Marks3" : 78 } { "_id" : ObjectId("5e77833abbc41e36cc3caeac"), "Name" : "David", "Marks1" : 50, "Marks2" : 57, "Marks3" : 68 } { "_id" : ObjectId("5e77833bbbc41e36cc3caead"), "Name" : "Bob", "Marks1" : 65, "Marks2" : 71, "Marks3" : 0 }