jpa的级联删除 在SSH2框架内执行失败，求指导啊解决方案

package wxm.domain;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToMany;//城市类@Entitypublic class City {    @Id    @GeneratedValue    private Integer cId;    @Column(length = 20)    private String cName;    // 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 = "city")    private Set<Garage> garages = new HashSet<Garage>(0);    public Integer getcId() {        return cId;    }    public void setcId(Integer cId) {        this.cId = cId;    }    public String getcName() {        return cName;    }    public void setcName(String cName) {        this.cName = cName;    }    public Set<Garage> getGarages() {        return garages;    }    public void setGarages(Set<Garage> garages) {        this.garages = garages;    }}

package wxm.domain;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.OneToMany;//车库类@Entitypublic class Garage {    private Integer gid;    private String garagenum;    private City city;    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;    }    @ManyToOne()    @JoinColumn(name = "cityId")    public City getCity() {        return city;    }    public void setCity(City city) {        this.city = city;    }    public void addGarageAuto(Auto auto) {        auto.setGarage(this);        this.autos.add(auto);    }}

package wxm.domain;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;//汽车类 @Entitypublic 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;    }}