休眠收集缓存问题

问题描述

| 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\",length = 1000)
  public String getName() {
    return name;
  }

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

  ...

}

我有以下用于测试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);

有人可以解释一下为什么最后一行失败吗？     

解决方法

        它肯定会失败，因为您正在同一事务中执行所有这些操作，因此始终从会话缓存中返回同一VehicleBrand实例。 由于您在创建VehicleModel时忘记了维护关联的双方（即，您将品牌分配给了新模型，但是却忘记了将创建的模型添加到品牌的模型集合中），因此相同的模型集是始终返回，并且不包含新创建的模型。