Hibernate 集合缓存问题

Question

我有以下 2 个 Hibernate 实体：

@Entity
@Table(name = "VEHICLE_BRAND")
public class VehicleBrand implements java.io.Serializable {

  ...

  @Column(name = "NAME", nullable = false, length = 1000)
  public String getName() {
    return name;
  }

  @OneToMany(fetch = FetchType.LAZY, mappedBy = "vehiclebrand")
  public Set<VehicleModel> getVehicleModels() {
    return vehicleModels;
  }

  ...

}

和

@Entity
@Table(name = "VEHICLE_MODEL")
public class VehicleModel implements java.io.Serializable {

  ...

  @Column(name = "NAME", nullable = false, length = 1000)
  public String getName() {
    return name;
  }

  @ManyToOne(fetch=FetchType.LAZY)
  @JoinColumn(name="VECHILE_BRAND_ID")
  public VehicleBrand getVehicleBrand() {
    return this.vehicleBrand;
  }

  ...

}

我有以下测试 VehicleBrand 和 VehicleModel 的单元测试：

DefaultTransactionDefinition txDef = new DefaultTransactionDefinition();
txDef.setName("test1");
txDef.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED);
TransactionStatus txStatus = txManager.getTransaction(txDef);

// Load brand "1" object.
VehicleBrand brand = (VehicleBrand) factory.getVehicleBrandDAO().findFirstByName("1");
assertNotNull(brand);

// Check if model "X" exists for brand "1" through collection.
Set<VehicleModel> models = brand.getVehicleModels();
for (final VehicleModel model : models) {
  assertFalse(model.getName().equals("X"));
}

// Add model "X" to brand "1".
VehicleModel model = new VehicleModel();
model.setName("X");
model.setValidFrom(new Date());
model.setVehicleBrand(brand);
factory.getVehicleModelDAO().create(model);

txManager.commit(txStatus);

txDef = new DefaultTransactionDefinition();
txDef.setName("test2");
txDef.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED);
txStatus = txManager.getTransaction(txDef);

// Check that model is added to database.
model = (VehicleModel) factory.getVehicleModelDAO().findFirstByName("X");
assertNotNull(model);
assertEquals(model.getVehicleBrandId().longValue(), 1L);

// Check if model X exists for brand "1" through collection.
brand = (VehicleBrand) factory.getVehicleBrandDAO().findFirstByName("1");
models = brand.getVehicleModels();
boolean found = false;
for (final VehicleModel model2 : models) {
  if (model2.getName().equals("X")) {
    found = true;
  }
}
assertTrue(found);

txManager.commit(txStatus);

谁能解释一下为什么最后一行失败了？

Answer 1

它肯定会失败，因为您在同一个事务中执行所有这些，因此总是从会话缓存中返回同一个 VehicleBrand 实例。

由于您在创建 VehicleModel 时忘记维护关联的双方（即，您将品牌分配给新模型，但忘记将创建的模型添加到品牌的模型集合中），因此同一组模型是总是返回，并且不包含新创建的模型。