在不更改Core Data对象的情况下，从NSFectchRequest修改结果数组的正确方法

I am retrieving a fetch from my core data database and trying to iterate through the data and make changes to the data, if necessary. When I change the data in the results array, it turns out that my database is changing in the back end as well, without doing a save. I am wondering what would be a good practice to use to change the data without affecting the back end data.I am retrieving a fetch from my core data datab