如何将 Builder 模式用于带有 JPA 的实体

Question

我读到，当你有一个带有很多参数的类时，使用构建器模式很有用。我想知道如何使用构建器模式来实现实体。如果您能提供示例代码那就太好了。

Answer 1

当然这是可能的，您只需为每个实体提供一个（可能是嵌套的）构建器即可。

这是一个有效的示例：

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class FluentEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String someName;
    private int someNumber;
    private boolean someFlag;

    protected FluentEntity(){}

    private FluentEntity(String someName, int someNumber, boolean someFlag) {
        this.someName = someName;
        this.someNumber = someNumber;
        this.someFlag = someFlag;
    }

    public long getId() {
        return id;
    }

    public String getSomeName() {
        return someName;
    }

    public int getSomeNumber() {
        return someNumber;
    }

    public boolean isSomeFlag() {
        return someFlag;
    }

    public static FluentEntityBuilder builder() {
        return new FluentEntityBuilder();
    }

    public static class FluentEntityBuilder {

        private String someName;
        private int someNumber;
        private boolean someFlag;

        public FluentEntityBuilder setSomeName(final String someName) {
            this.someName = someName;
            return this;
        }

        public FluentEntityBuilder setSomeNumber(final int someNumber) {
            this.someNumber = someNumber;
            return this;
        }

        public FluentEntityBuilder setSomeFlag(final boolean someFlag) {
            this.someFlag = someFlag;
            return this;
        }

        public FluentEntity build() {
            return new FluentEntity(someName, someNumber, someFlag);
        }

    }

}

使用它的代码如下：

FluentEntity entity = FluentEntity.builder().setSomeName(someName).setSomeNumber(someNumber)
                .setSomeFlag(someFlag).build();

请记住，如果有的话，您必须排除自动生成的字段，例如主键（在此示例中 id）。

如果您想摆脱为每个实体创建构建器类的“样板”代码，我会推荐一个方便的库，例如 Lombok。然后，您只需注释您的实体即可获得您的构建器（甚至更多），也许需要花费一些额外的工作来排除 id 字段。

您应该看看 Project Lombok

不过，这里有一些代码测试此构建器（使用 Spring Boot 和 Hibernate 实现）。

存储库：

import org.springframework.data.repository.CrudRepository;

import com.example.model.FluentEntity;

public interface FluentEntityRepository extends CrudRepository<FluentEntity, Long> {

}

这里有一些测试：

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.CoreMatchers.notNullValue;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.greaterThan;

import java.util.stream.StreamSupport;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Transactional;

import com.example.model.FluentEntity;

@RunWith(SpringRunner.class)
@Transactional
@SpringBootTest
public class FluentEntityRepositoryTests {

    @Autowired
    private FluentEntityRepository fluentEntityRepository;

    @Test
    public void insertAndReceiveFluentEntityCreatedWithBuilder() {
        final String someName = "name";
        final int someNumber = 1;
        final boolean someFlag = true;

        FluentEntity entity = FluentEntity.builder().setSomeName(someName).setSomeNumber(someNumber)
                .setSomeFlag(someFlag).build();

        entity = fluentEntityRepository.save(entity);
        assertThat("Entity did not get a generated Id!", entity.getId(), greaterThan(-1L));
        assertThat("Entity name did not match!", entity.getSomeName(), is(someName));
        assertThat("Entity number did not match!", entity.getSomeNumber(), is(someNumber));
        assertThat("Entity flag did not match!", entity.isSomeFlag(), is(someFlag));
    }

    @Test
    public void insertSomeAndReceiveFirst() {
        fluentEntityRepository.save(FluentEntity.builder().setSomeName("A").setSomeNumber(1).setSomeFlag(true).build());
        fluentEntityRepository
                .save(FluentEntity.builder().setSomeName("B").setSomeNumber(2).setSomeFlag(false).build());
        fluentEntityRepository.save(FluentEntity.builder().setSomeName("C").setSomeNumber(3).setSomeFlag(true).build());

        final Iterable<FluentEntity> findAll = fluentEntityRepository.findAll();
        assertThat("Should get some iterable!", findAll, notNullValue());

        final FluentEntity fluentEntity = StreamSupport.stream(findAll.spliterator(), false).findFirst().get();
        assertThat("Should get some entity!", fluentEntity, notNullValue());
    }

}