Get the array of _id in MongoDB?

MongoDBDatabaseBig Data Analytics

The _id in MongoDB is a field, which is mandatory. In MongoDB, each document stored in a collection requires a unique _id field that acts as a primary key. Following is the syntax to get the array of all the ids i.e. _id in MongoDB

db.yourCollectionName.find({ _id : { $in : [yourValue1,yourValue2,yourValue3,.......N] } } ); Let us first implement the following query to create a collection with documents > db.selectInWhereIdDemo.insertOne({"_id":23}); { "acknowledged" : true, "insertedId" : 23 } > db.selectInWhereIdDemo.insertOne({"_id":28}); { "acknowledged" : true, "insertedId" : 28 } > db.selectInWhereIdDemo.insertOne({"_id":45}); { "acknowledged" : true, "insertedId" : 45 } > db.selectInWhereIdDemo.insertOne({"_id":75}); { "acknowledged" : true, "insertedId" : 75 } > db.selectInWhereIdDemo.insertOne({"_id":85}); { "acknowledged" : true, "insertedId" : 85 } > db.selectInWhereIdDemo.insertOne({"_id":145}); { "acknowledged" : true, "insertedId" : 145 } Following is the query to display all the documents from the collection with the help of find() method > db.selectInWhereIdDemo.find().pretty(); This will produce the following output { "_id" : 23 } { "_id" : 28 } { "_id" : 45 } { "_id" : 75 } { "_id" : 85 } { "_id" : 145 } Following is the query to get _id i.e. all the ids in an array > db.selectInWhereIdDemo.find({ _id : {$in : [23,45,85,145] } } );

This will produce the following output

{ "_id" : 23 }
{ "_id" : 45 }
{ "_id" : 85 }
{ "_id" : 145 }
Published on 11-Apr-2019 12:00:18