JPA to JSON with only primary key/normalize data

Question

I have two JPA Entities (Patient and Clinic) with OneToMany ManyToOne relationship. I would like to return the data in JSON format (currently with org.apache.cxf.jaxrs.provider.JSONProvider). Below is a patient info and its associated clinic. However, it returns all fields for clinic. How could I just return primary key/id (@Id) for the clinic?

{
    "Patient": {
        "age": 0,
        "clinic": {
            "address": "long address here",
            "otherKeys": "other values",
            "id": 5
        },
        "ic": "010101",
        "id": 12,
        "name": "Patient 01"
    }
}