多对一映射@ManyToOne添加数据问题

Question

两个实体类ProjectBudget.java,Project.java，双向一对多，多对一映射映射
如下：
ProjectBudget.java@Entity
@Table(name="project_budgets")
public class ProjectBudget{
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="project_id",nullable = false)
@JsonIgnore
private Project project;
getter and setter...
}Project.java@Entity
@Table(name = "projects")
@JsonIgnoreProperties(ignoreUnknown=true)
public class Project{
@OneToMany(fetch = FetchType.LAZY, mappedBy = "project")
private List<ProjectBudget> projectBudgets;
getter and setter...
}@RequestMapping(value="/add")
public ResponseEntity<HttpEntity> addProjectBudget(@Valid @RequestBody ProjectBudget projectBudget,Model model){

projectBudgetService.addBudget(projectBudget);
return new ResponseEntity(model,HttpStatus.OK);
}
project_budgets表中存储的是project Id
如何从页面添加一个Json格式的ProjectBudget实体?
关键是ProjectBudget实体中的project属性怎么添加？