Can Jersey find a POJO from an ID when mapping from JSON?

Question

It's hard to put this into words, but I'll do my best.

High Level: I am writing a web service to add a new PrblFldr entity to the database, but I need to associate the proper PrblTmplt with it (please ignore the terrible naming scheme, I didn't do it). I am POSTing JSON, which Jersey maps to the correct POJOs. But, instead of calling the POJO's constructor for one of the fields, I want it to use the EntityManager to find the correct object based on an ID.

Low Level: Here's a sample of the JSON I am currently trying to pass to my web service:

{
    fldrNm: "test",
    prblTmplt: {
        tmpltSeqId: 4
    }
}

Here's the code on the other side, where the web service sits:

@POST
@Consumes(MediaType.APPLICATION_JSON)
@Path("/folders/create")
public Response createFolder(PrblFldr folder) {
    em.persist(folder);
    return Response.ok(gson.toJson(folder), MediaType.APPLICATION_JSON).build();
}

Now, here's what the PrblFldr entity looks like, with a lot of irrelevant fields omitted:

@Entity
@Table(name="PRBL_FLDR")
@NamedQuery(name="PrblFldr.findAll", query="SELECT p FROM PrblFldr p")
public class PrblFldr implements Serializable {

    @Expose
    @Column(name="FLDR_NM")
    private String fldrNm;

    //bi-directional many-to-one association to PrblTmplt
    @Expose
    @ManyToOne
    @JoinColumn(name="FLDR_TYP_SEQ_ID", insertable=false, updatable=false)
    private PrblTmplt prblTmplt;

    // other fields...
}

See how that prblTmplt field is joined on FLDR_TYP_SEQ_ID? I need to get from that ID to the object. Lastly, here is what our PrblTmplt class looks like, again with only relevant information included:

@Entity
@Table(name="PRBL_TMPLT")
@NamedQuery(name="PrblTmplt.findAll", query="SELECT p FROM PrblTmplt p")
public class PrblTmplt implements Serializable {

    @Expose
    @SerializedName("id")
    @Id
    @Column(name="TMPLT_SEQ_ID")
    private long tmpltSeqId;

    // other fields...
}

The ultimate goal is to prevent the need for creating some intermediate POJO that Jersey maps to, only to turn right around to fill out the relevant fields in a new PrblFldr object (and use em.find() to actually find the PrblTmplt we're using). I'm not sure if what I'm talking about is possible, but after searching for hours, I figured I would ask you guys.

EDIT: To more clearly specify my situation, the above code (when I log what the web service sends back) outputs JSON like this:

{
    fldrNm: "test",
    prblTmplt: {
        tmpltSeqId: 4
    }
}

... which is exactly what I put in. Instead, I want that tmpltSeqId to be used as a lookup PK to fetch the object that exists with that ID in the DB, so a return might look something like this:

{
    fldrNm: "test",
    prblTmplt: {
        tmpltSeqId: 4,
        tmpltDesc: "sample description",
        tmpltNm: "sample template name",
        // etc...
    }
}

Answer 1

I decided against my original thought of having all this happen automatically. Instead, I created my own "intermediate entity" POJOs that I have allowed JAXB to map to. I will then perform my own JPA lookups and build my actual entity manually. Looking back, this is probably a more proper way to do this since you avoid ambiguity by performing the process by hand.