How do you update objects in a document's array (nested updating)

mongodb

Solution

For question #1, let's break it into two parts. First, increment any document that has "items.item_name" equal to "my_item_two". For this you'll have to use the positional "$" operator. Something like:

 db.bar.update( {user_id : 123456 , "items.item_name" : "my_item_two" } , 
                {$inc : {"items.$.price" : 1} } , 
                false , 
                true);

Note that this will only increment the first matched subdocument in any array (so if you have another document in the array with "item_name" equal to "my_item_two", it won't get incremented). But this might be what you want.

The second part is trickier. We can push a new item to an array without a "my_item_two" as follows:

 db.bar.update( {user_id : 123456, "items.item_name" : {$ne : "my_item_two" }} , 
                {$addToSet : {"items" : {'item_name' : "my_item_two" , 'price' : 1 }} } ,
                false , 
                true);

For your question #2, the answer is easier. To increment the total and the price of item_three in any document that contains "my_item_three," you can use the $inc operator on multiple fields at the same time. Something like:

db.bar.update( {"items.item_name" : {$ne : "my_item_three" }} ,
               {$inc : {total : 1 , "items.$.price" : 1}} ,
               false ,
               true);

Problem

Assume we have the following collection, which I have few questions about: ``` { "_id" : ObjectId("4faaba123412d654fe83hg876"), "user_id" : 123456, "total" : 100, "items" : [ { "item_name" : "my_item_one", "price" : 20 }, { "item_name" : "my_item_two", "price" : 50 }, { "item_name" : "my_item_three", "price" : 30 } ] } ``` I want to increase the price for "item_name":"my_item_two" and if it doesn't exists, it should be appended to the "items" array. How can I update two fields at the same time? For example, increase the price for "my_item_three" and at the same time increase the "total" (with the same value). I prefer to do this on the MongoDB side, otherwise I have to load the document in client-side (Python) and construct the updated document and replace it with the existing one in MongoDB. This is what I have tried and works fine if the object exists: ``` db.test_invoice.update({user_id : 123456 , "items.item_name":"my_item_one"} , {$inc: {"items.$.price": 10}}) ``` However, if the key doesn't exist, it does nothing. Also, it only updates the nested object. There is no way with this command to update the "total" field as well.

Original source