Json – org.codehaus.jackson.map.JsonMappingException: Can not instantiate value of type [simple type, class models.Job] from JSON String

i use the playframework and tried to deserialize some json into a java object.
It worked fine, exept the relationship in the model. I got the following exception

enter code hereorg.codehaus.jackson.map.JsonMappingException: Can not
instantiate value of type [simple type, class models.Job] from JSON
String; no single-String constructor/factory method (through reference
chain: models.Docfile["job"])

i thought jackson in combination with play could do that:

this is the json

{"name":"asd","filepath":"blob","contenttype":"image/png","description":"asd","job":"1"}

and this my code, nothing special:

public static Result getdata(String dataname) {
        ObjectMapper mapper = new ObjectMapper();
        try {
            Docfile docfile = mapper.readValue((dataname), Docfile.class);
            System.out.println(docfile.name);
            docfile.save();

        } catch (JsonGenerationException e) {

            e.printStackTrace();

        } catch (JsonMappingException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        }

        return ok();
    }

Hope there is help for me, thanks
Markus

UPDATE:

Docfile Bean:

package models;

import java.util.*;

import play.db.jpa.*;
import java.lang.Object.*;
import play.data.format.*;
import play.db.ebean.*;
import play.db.ebean.Model.Finder;
import play.data.validation.Constraints.*;
import play.data.validation.Constraints.Validator.*;

import javax.persistence.*;

import com.avaje.ebean.Page;

@Entity
public class Docfile extends Model {

    @Id
    public Long id;

    @Required
    public String name;

    @Required
    public String description;

    public String filepath;

    public String contenttype;

    @ManyToOne
    public Job job;

    public static Finder<Long,Docfile> find = new Model.Finder(
            Long.class, Docfile.class
            );




    public static List<Docfile> findbyJob(Long job) {
        return find.where()
                .eq("job.id", job)
                .findList();
    }

    public static Docfile create (Docfile docfile, Long jobid) {
        System.out.println(docfile);
        docfile.job = Job.find.ref(jobid);
        docfile.save();
        return docfile;
    }
}