Update Field in MongoDB but need to consider old value-CodePudding

How to Update a field by reading the old value from the document then update a new value to that field in MongoDB.

suppose in a document i have a field named Qty and it already has a value like Qty = 2; now i need to update the Qty = 5; So after update i need the Qty be 2 5 = 7; no directly replace 2 with 5. please help me.

CodePudding user response：

Suppose you have a model like below.

    db.products.insertOne(
       {
         _id: 1,
         sku: "foo",
         quantity: 2,
        
       }
    )

The following updateOne() operation uses the $inc operator to:

increase the quantity field by 2

    db.products.updateOne(
       { sku: "foo" },
       { $inc: { quantity: 2 } }
    )