There are several options which you can use, among which:
- Add (a) column(s) to your view which is eligible as a PK, and use that as a PK for your entity. It doesn't have to be a PK in the database.
- define a composite primary key in your entities. You can define a primary key composed of all columns in your entity if completely duplicate entities do not exist. If you can find a number of columns which will never have the same value more than once, create your composite key. It doesn't have to be a PK in the database.