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How to merge multiple documents in MongoDB?
To merge multiple documents in MongoDB, use aggregate(). Let us create a collection with documents −
> db.demo436.insertOne( ... { ... "_id" : "101", ... "Name": "Chris", ... "details" : [ ... { ... "CountryName" : "US", ... "Age" : 21 ... } ... ], ... "Price" : 50 ... } ... ); { "acknowledged" : true, "insertedId" : "101" } > db.demo436.insertOne( ... { ... "_id" : "102", ... "Name": "Chris", ... "details" : [ ... { ... "CountryName" : "UK", ... "Age" : 22 ... } ... ], ... "Price" : 78 ... } ... ); { "acknowledged" : true, "insertedId" : "102" } > db.demo436.insertOne( ... { ... "_id" : "103", ... "Name": "Chris", ... "details" : [ ... { ... "CountryName" : "US", ... "Age" : 21 ... } ... ], .. . "Price" : 50 ... } ... ); { "acknowledged" : true, "insertedId" : "103" }
Display all documents from a collection with the help of find() method −
> db.demo436.find();
This will produce the following output −
{ "_id" : "101", "Name" : "Chris", "details" : [ { "CountryName" : "US", "Age" : 21 } ], "Price" : 50 } { "_id" : "102", "Name" : "Chris", "details" : [ { "CountryName" : "UK", "Age" : 22 } ], "Price" : 78 } { "_id" : "103", "Name" : "Chris", "details" : [ { "CountryName" : "US", "Age" : 21 } ], "Price" : 50 }
Following is the query to merge multiple documents in MongoDB −
> db.demo436.aggregate([ ... {$sort: {_id: 1, Name: 1}}, ... {$unwind: '$details'}, ... {$group: {_id: '$Name', details: {$push: '$details'}, ... Price: {$sum: '$Price'}, ... id: {$last: {$concat: ["$_id", "_", "AppendedValue" ]}}, ... Name: {$last: '$Name'}}}, ... {$addFields: {Id: 'NewIdAppped', _id: '$id'}}, ... {$project: {"id": 0 }}])
This will produce the following output −
{ "_id" : "103_AppendedValue", "details" : [ { "CountryName" : "US", "Age" : 21 }, { "CountryName" : "UK", "Age" : 22 }, { "CountryName" : "US", "Age" : 21 } ], "Price" : 178, "Name" : "Chris", "Id" : "NewIdAppped" }
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