请问jpa删除实体有级联关系删不掉怎么办？

/**  
 * many to one 一对多关联 
 */ 

import java.util.HashSet;   
import java.util.Set;   
import javax.persistence.CascadeType;   
import javax.persistence.Column;   
import javax.persistence.Entity;   
import javax.persistence.FetchType;   
import javax.persistence.GeneratedValue;   
import javax.persistence.Id;   
import javax.persistence.OneToMany;   
@Entity  
public class Garage {   
    private Integer gid;   
    private String garagenum;   
    private Set<Auto> autos = new HashSet<Auto>();         
    @Id @GeneratedValue  
    public Integer getGid() {   
        return gid;   
    }   
    public void setGid(Integer gid) {   
        this.gid = gid;   
    }   
    @Column(length=20)   
    public String getGaragenum() {   
        return garagenum;   
    }   
    public void setGaragenum(String garagenum) {   
        this.garagenum = garagenum;   
    }   
    //CascadeType属性有四个值，其中REMOVE属性是实现级联删除，要实现级联删除
    //在父栏必需添加CascadeType.REMOVE标注，这是级联删除的关键
    @OneToMany(cascade={CascadeType.REMOVE},mappedBy="garage")  
    public Set<Auto> getAutos() {   
        return autos;   
    }   
    public void setAutos(Set<Auto> autos) {   
        this.autos = autos;   
    }   
    public void addGarageAuto(Auto auto) {   
        auto.setGarage(this);   
        this.autos.add(auto);   
    }   
}

Auto.java

/**  
 * one to many 多对一关联  
 */ 

import javax.persistence.CascadeType;   
import javax.persistence.Entity;   
import javax.persistence.GeneratedValue;   
import javax.persistence.Id;   
import javax.persistence.JoinColumn;   
import javax.persistence.ManyToOne;   
@Entity  
public class Auto {    
    private Integer autoId;   
    private String autotype;   
    private String autonum;   
    private Garage garage;   
    @Id @GeneratedValue  
    public Integer getAutoId() {   
        return autoId;   
    }   
    public void setAutoId(Integer autoId) {   
        this.autoId = autoId;   
    }   
    public String getAutotype() {   
        return autotype;   
    }   
    public void setAutotype(String autotype) {   
        this.autotype = autotype;   
    }   
    public String getAutonum() {   
        return autonum;   
    }   
    public void setAutonum(String autonum) {   
        this.autonum = autonum;   
    }   
    @ManyToOne()   
    @JoinColumn(name="garageid")   
    public Garage getGarage() {   
        return garage;   
    }   
    public void setGarage(Garage garage) {   
        this.garage = garage;   
    }   
}