When To Use MongoDB's $elemMatch

You have an e-commerce database. You want to find all orders where a customer bought a laptop for more than $1000. Simple query, right? db . orders . find ({ " items.category " : " laptop " , " items.price " : { $gt : 1000 } }) Except this returns orders where the customer bought any laptop AND any item over $1000 - even if the laptop itself cost $50. This is MongoDB's most common query mistake. Let's see why it happens and how to fix it. The Problem: Array Query Logic Here's sample data from an e-commerce orders collection: { _id : 1 , customer : " Alice " , items : [ { category : " laptop " , price : 1200 , name : " MacBook Pro " }, { category : " mouse " , price : 25 , name : " Wireless Mouse " } ] } { _id : 2 , customer : " Bob " , items : [ { category : " laptop " , price : 500 , name : " Chromebook " }, { category : " monitor " , price : 1500 , name : " 4K Display " } ] } What you want: Orders where someone bought a laptop costing more than $1000 (Alice's order only) What this qu