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Decrement only a single value in MongoDB?
Let us first create a collection with documents −
>db.decrementingOperationDemo.insertOne({"ProductName":"Product-1","ProductPrice":756}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7a8ae6d78f205348bc63c") } >db.decrementingOperationDemo.insertOne({"ProductName":"Product-2","ProductPrice":890}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7a8b86d78f205348bc63d") } >db.decrementingOperationDemo.insertOne({"ProductName":"Product-3","ProductPrice":994}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7a8c66d78f205348bc63e") } >db.decrementingOperationDemo.insertOne({"ProductName":"Product-4","ProductPrice":1000}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7a8d06d78f205348bc63f") }
Following is the query to display all documents from a collection with the help of find() method −
> db.decrementingOperationDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5cd7a8ae6d78f205348bc63c"), "ProductName" : "Product-1", "ProductPrice" : 756 } { "_id" : ObjectId("5cd7a8b86d78f205348bc63d"), "ProductName" : "Product-2", "ProductPrice" : 890 } { "_id" : ObjectId("5cd7a8c66d78f205348bc63e"), "ProductName" : "Product-3", "ProductPrice" : 994 } { "_id" : ObjectId("5cd7a8d06d78f205348bc63f"), "ProductName" : "Product-4", "ProductPrice" : 1000 }
Following is the query decrement a single value −
> db.decrementingOperationDemo.update({_id: ObjectId("5cd7a8d06d78f205348bc63f"), ProductPrice: {$gt: 0}}, {$inc: {ProductPrice: -10}}); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
Let us check the document once again −
> db.decrementingOperationDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5cd7a8ae6d78f205348bc63c"), "ProductName" : "Product-1", "ProductPrice" : 756 } { "_id" : ObjectId("5cd7a8b86d78f205348bc63d"), "ProductName" : "Product-2", "ProductPrice" : 890 } { "_id" : ObjectId("5cd7a8c66d78f205348bc63e"), "ProductName" : "Product-3", "ProductPrice" : 994 } { "_id" : ObjectId("5cd7a8d06d78f205348bc63f"), "ProductName" : "Product-4", "ProductPrice" : 990 }
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