[{"_id":"root_id","products":[{"id":"p1","code":"TRAILING "},{"id":"p2","code":" LEADING"},{"id":"p3","code":"CLEAN"}]}]

db.collection.update({},[{$set:{products:{$map:{input:"$products",in:{$mergeObjects:["$$this",{code:{$trim:{input:"$$this.code"}}}]}}}}}],{multi:true})