[{"key":1,data:[{name:"Link 1",url:"hello"},{name:"Link 2",url:"world"},]},{"key":2,data:[{name:"Link 3",url:"hello"},{name:"Link 4",url:"hello"},]}]

db.collection.update({},{$set:{"data.$[element].url":"boo"}},{arrayFilters:[{"element.url":"hello"}],multi:true})