Question

我设计的数据库使用 Table Per Class 的继承策略，其中公共字段存在于派生表中以及父表中。一些简单的模型看起来像这样。

Vehicle.java

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Vehicle {

    @Id @GeneratedValue
    private int id;

    private String name;

    private String brand;

}

Car.java

@Entity
public class Car extends Vehicle {

    private String oil;

}

Bike.java

@Entity
public class Bike extends Vehicle {

    private String frame;

}

现在，我想对所有类型的VehicleRepository个对象进行统一Vehicle，包括Car和Bike。

存储库可能看起来像这样。

VehicleRepository.java

@Repository
public interface VehicleRepository extends CrudRepository<Vehicle, Integer> {

    @Query("SELECT v FROM Vehicle e WHERE v.vehicleId = ?1")
    public Vehicle findById(Integer vehicleId);

}

所以我希望能够做类似的事情。

int carId = 3; // I know that in the DB there's a car with that ID
int bikeId = 7; // I know that in the DB there's a bike with that ID

// the important part
Car car = (Car) repo.findById(carId);
Bike bike = (Bike) repo.findById(bikeId);

// now I want to be able to call:
car.getOil();
bike.getFrame();

问题是：这是否有效，这是一个很好的模式吗？

Answer 1

您可以在Vehicle中添加所有字段，并尝试使用Car Bike和@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) public class Vehicle { @Id @GeneratedValue private int id; private String name; private String brand; private String oil; private String frame; }。

Car

对于Bike和public interface VehicleProjection { public int getId(); public String getBrand(); public String getName(); } public interface Car extends VehicleProjection { public String getOil(); } public interface Bike extends VehicleProjection { public String getFrame(); }，您可以使用投影：

public interface CarRepository extends Repository<Vehicle, Integer> {
    public Car findById(Integer carId);

}

您的存储库应如下所示：

Bike

import os import glob import csv def check(filename): if 'DELIVERY NOTIFICATION' in open(filename).read(): isDenied = True print ("This claim was Denied") print (isDenied) elif 'Dear Customer:' in open(filename).read(): isDenied = False print("This claim was Approved") print (isDenied) else: print("I don't know if this is approved or denied") def iterate(): path = 'text/' for infile in glob.glob(os.path.join(path, '*.txt')): print ('current file is:' + infile) filename = infile check(filename) iterate()存储库

相同

从数据库查询获取派生类

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