2

我想使用 Spring Data JDBC 和 PostgreSQL 对一对一关系进行建模，但我无法以正确的方式设置根聚合。

有以下场景：图片，SQL
每个引擎都是唯一的，car有唯一的列engine_id是 的外键engine.id，同样适用truck。因此汽车和卡车应该是根聚合，所以当汽车或卡车被删除时，引擎表中的引用行也应该被删除。

根据我对Spring Data JDBC Aggregates的理解

如果多个聚合引用同一个实体，则该实体不能是引用它的那些聚合的一部分，因为它只能是一个聚合的一部分。

所以问题是：

  • 由于上面的解释，解决方法是否可行，以便通过执行 CRUD 操作car并将truck更改也反映到engine？
  • 使用 Spring Data JDBC 在 java 中实现这种关系的最佳方法是什么？

这是我的看法，它不起作用，但应该澄清我想要完成的事情。

汽车.java

package com.example.dao.model;

import org.springframework.data.annotation.Id;
import org.springframework.data.domain.Persistable;
import org.springframework.data.relational.core.mapping.Column;
import org.springframework.data.relational.core.mapping.Table;

import java.util.UUID;

@Table("car")
public class Car implements Persistable<UUID> {

    @Id
    private UUID id;

    String brand;

    String model;

    @Column("engine_id")
    Engine engine;

    public void setId(UUID id) {
        this.id = id;
    }

    @Override
    public UUID getId() {
        return id;
    }

    @Override
    public boolean isNew() {
        return id == null;
    }
}

引擎.java

package com.example.dao.model;

import org.springframework.data.annotation.Id;
import org.springframework.data.domain.Persistable;
import org.springframework.data.relational.core.mapping.Table;

import java.time.LocalDateTime;
import java.util.UUID;

@Table("engine")
public class Engine implements Persistable<UUID> {

    @Id
    private UUID id;

    String name;

    LocalDateTime dateCreated;

    String type;

    public void setId(UUID id) {
        this.id = id;
    }

    @Override
    public UUID getId() {
        return id;
    }

    @Override
    public boolean isNew() {
        return id == null;
    }
}

卡车.java

package com.example.dao.model;

import org.springframework.data.annotation.Id;
import org.springframework.data.domain.Persistable;
import org.springframework.data.relational.core.mapping.Column;
import org.springframework.data.relational.core.mapping.Table;

import java.util.UUID;

@Table("truck")
public class Truck implements Persistable<UUID> {

    @Id
    private UUID id;

    String brand;

    String model;

    Integer cargoMaxWeight;

    String truckType;

    @Column("engine_id")
    Engine engine;

    public void setId(UUID id) {
        this.id = id;
    }

    @Override
    public UUID getId() {
        return id;
    }

    @Override
    public boolean isNew() {
        return id == null;
    }
}
4

2 回答 2

6

我看到了用 Java 建模的四个选项。请注意，它们中的大多数都需要调整您的数据库模式。

一般的问题是 Spring Data JDBC 假定被引用的实体 ( Engine) 在其表中有一个引用拥有实体 ( Car/ Vehicle) 的列。这有一个问题：https : //jira.spring.io/browse/DATAJDBC-128 从这里开始，您有以下选项：

  1. 将列添加到引擎表中，生成如下所示的实体和架构（所有实体都减少到与问题相关的最小值）：

    public class Car {

    @Id
    Long id;
    String name;

    Engine engine;
}

public class Truck {

    @Id
    Long id;
    String name;

    Engine engine;
}

public class Engine {

    String name;
}

CREATE TABLE CAR (
  id   BIGINT IDENTITY,
  NAME VARCHAR(200)
);

CREATE TABLE TRUCK (
  ID   BIGINT IDENTITY,
  NAME VARCHAR(200)
);

CREATE TABLE ENGINE (
  TRUCK BIGINT,
  CAR   BIGINT,
  NAME  VARCHAR(200),
  FOREIGN KEY (TRUCK) REFERENCES TRUCK (ID),
  FOREIGN KEY (CAR) REFERENCES CAR (ID)
);

    我在 GitHub 上提供了一个完整的示例：https ://github.com/schauder/so-sd-jdbc-multipleonetoone 。

  2. 如果您不喜欢这两列，您可以修改映射以将同一列用于两个引用。但是你必须确保 和 的 idCar是Vehicle不同的。即使这样，这种方法也存在一个大问题：

    deleteAll在Car存储库或Truck车辆上将删除所有引擎！！！ 因此不推荐这种方法！

    如果您仍想在此处使用它，这里是模式和实体的代码。

    public class Car {

    @Id
    Long id;
    String name;

    @Column(value = "vehicle")
    Engine engine;
}

public class Truck {

    @Id
    Long id;
    String name;

    @Column(value = "vehicle")
    Engine engine;
}

public class Engine {

    String name;
}


CREATE TABLE CAR (
  id   BIGINT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY ,
  NAME VARCHAR(200)
);

CREATE TABLE TRUCK (
  ID   BIGINT GENERATED BY DEFAULT AS IDENTITY (START WITH -1, INCREMENT BY -1) PRIMARY KEY ,
  NAME VARCHAR(200)
);

CREATE TABLE ENGINE (
  VEHICLE   BIGINT,
  NAME  VARCHAR(200),
);

    完整的示例在此提交上：https ://github.com/schauder/so-sd-jdbc-multipleonetoone/tree/5570979ef85e30fe7a17a8ce48d867fdb79e212a 。

  3. 有两个单独的Engine类和表。一个给Cars，一个给Trucks。

  4. 如果您不想或不能更改您的数据库架构，您可以考虑Engine、Car和Truck三个单独的聚合。你会有一个Long engineIdinCar和 in Truck。然后可以使用事件侦听器AfterDeleteEvent来完成级联删除。

于 2018-12-05T09:03:39.087 回答
1

设法找到解决方案，问题是当在数据库中模型不同时，我无法理解来自 的引用Car和Truck类。Engine

汽车.java

package com.backend.dao.model;

import org.springframework.data.annotation.Id;
import org.springframework.data.domain.Persistable;

import java.util.Objects;
import java.util.UUID;

public class Car implements Persistable<UUID> {

    @Id
    private UUID id;

    private String brand;

    private String model;

    public void setId(UUID id) {
        this.id = id;
    }

    @Override
    public UUID getId() {
        return id;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    @Override
    public boolean isNew() {
        return id == null;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Car)) {
            return false;
        }
        Car car = (Car) o;
        return Objects.equals(id, car.id) &&
            Objects.equals(brand, car.brand) &&
            Objects.equals(model, car.model);
    }

    @Override
    public int hashCode() {

        return Objects.hash(id, brand, model);
    }
}

卡车.java

package com.backend.dao.model;

import org.springframework.data.annotation.Id;
import org.springframework.data.domain.Persistable;
import org.springframework.data.relational.core.mapping.Table;

import java.util.Objects;
import java.util.UUID;

@Table("truck")
public class Truck implements Persistable<UUID> {

    @Id
    private UUID id;

    private String brand;

    private String model;

    private Integer cargoMaxWeight;

    private String truckType;

    public void setId(UUID id) {
        this.id = id;
    }

    @Override
    public UUID getId() {
        return id;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public Integer getCargoMaxWeight() {
        return cargoMaxWeight;
    }

    public void setCargoMaxWeight(Integer cargoMaxWeight) {
        this.cargoMaxWeight = cargoMaxWeight;
    }

    public String getTruckType() {
        return truckType;
    }

    public void setTruckType(String truckType) {
        this.truckType = truckType;
    }

    @Override
    public boolean isNew() {
        return id == null;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Truck)) {
            return false;
        }
        Truck truck = (Truck) o;
        return Objects.equals(id, truck.id) &&
            Objects.equals(brand, truck.brand) &&
            Objects.equals(model, truck.model) &&
            Objects.equals(cargoMaxWeight, truck.cargoMaxWeight) &&
            Objects.equals(truckType, truck.truckType);
    }

    @Override
    public int hashCode() {

        return Objects.hash(id, brand, model, cargoMaxWeight, truckType);
    }
}

引擎.java

package com.backend.dao.model;

import org.springframework.data.annotation.Id;
import org.springframework.data.domain.Persistable;
import org.springframework.data.relational.core.mapping.Column;
import org.springframework.data.relational.core.mapping.Table;

import java.time.LocalDateTime;
import java.util.Objects;
import java.util.UUID;

@Table("engine")
public class Engine implements Persistable<UUID> {

    @Id
    private UUID id;

    private String name;

    private LocalDateTime dateCreated;

    private String type;

    @Column("engine_id")
    private Car car;

    @Column("engine_id")
    private Truck truck;

    public void setId(UUID id) {
        this.id = id;
    }

    @Override
    public UUID getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public LocalDateTime getDateCreated() {
        return dateCreated;
    }

    public void setDateCreated(LocalDateTime dateCreated) {
        this.dateCreated = dateCreated;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    @Override
    public boolean isNew() {
        return id == null;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Engine)) {
            return false;
        }
        Engine engine = (Engine) o;
        return Objects.equals(id, engine.id) &&
            Objects.equals(name, engine.name) &&
            Objects.equals(dateCreated, engine.dateCreated) &&
            Objects.equals(type, engine.type);
    }

    @Override
    public int hashCode() {

        return Objects.hash(id, name, dateCreated, type);
    }

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    public Truck getTruck() {
        return truck;
    }

    public void setTruck(Truck truck) {
        this.truck = truck;
    }
}

但是，此解决方案不满足要求 - 执行的 CRUD 操作Engine.java反映在Car.java和上Truck.java。Car.java而且 我想实现Truck.java在Engine.java.

如果有人有更好的解决方案，请发布。

于 2018-12-04T16:07:28.207 回答