JPA entityManager.merge 将 LocalDateTime 转换为 SQLServer 2012 DATETIME2

Question

我有一个以 DateTime 列作为主键的表：

USE [idatest]
GO

CREATE TABLE [dbo].[DatesTbl](
    [creationDate] [datetime] NOT NULL
 CONSTRAINT [PK_DatesTbl] PRIMARY KEY CLUSTERED
(
    [creationDate] ASC
))
GO

当我执行 entityManager.merge 时，我得到重复，PK 违规，因为 datetime 为 milisec 保留 3 位数字，但 hibernet 将其转换为 datetime2，它为 milisec 保留 7 位数字。 在 java 代码中，我使用 LocaDatetime，它包含 10 位毫秒数。

我已经尝试了在Hibernate MSSQL datetime2 映射中解释的解决方案，但它不起作用：Java 代码如下所示：pom.xml

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.3.RELEASE</version>
</parent>

<groupId>com.example</groupId>
<artifactId>spring-jap-test</artifactId>
<version>1.0-SNAPSHOT</version>
<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
    </plugins>
</build>

<dependencies>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
    </dependency>
    <dependency>
        <groupId>com.microsoft.sqlserver</groupId>
        <artifactId>mssql-jdbc</artifactId>
        <version>7.0.0.jre8</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
    </dependency>
</dependencies>

DatesTbl 类

@Entity
@NoArgsConstructor
@AllArgsConstructor
public class DatesTbl {

    @Column(columnDefinition = "DATETIME", nullable = false)
    @Id
    private LocalDateTime creationDate;
}

主类

@EnableTransactionManagement
public class Main {

    public static void main(String[] args) {

        ApplicationContext context = new AnnotationConfigApplicationContext(Main.class);

        EntityManagerFactory entityManagerFactory = context.getBean(EntityManagerFactory.class);
        final EntityManager entityManager = entityManagerFactory.createEntityManager();
        final LocalDateTime creationDate = LocalDateTime.of(2018, 12, 26, 8, 10, 40, 340);
        entityManager.getTransaction().begin();
        final DatesTbl datesTbl = entityManager.merge(new DatesTbl(creationDate));
        entityManager.getTransaction().commit();

        System.out.println("test");
    }

    @Bean
    @Primary
    public DataSource getDataSource() {

        SQLServerDataSource ds = null;
        try {
            ds = new SQLServerDataSource();
            ds.setServerName("localhost");
            ds.setDatabaseName("idatest");
            ds.setIntegratedSecurity(true);
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }
        return ds;
    }


    @Bean
    public JpaVendorAdapter jpaVendorAdapter() {
        HibernateJpaVendorAdapter hibernateJpaVendorAdapter = new HibernateJpaVendorAdapter();
        hibernateJpaVendorAdapter.setShowSql(true);
        hibernateJpaVendorAdapter.setGenerateDdl(true);
        hibernateJpaVendorAdapter.setDatabase(Database.SQL_SERVER);
        return hibernateJpaVendorAdapter;
    }


    @Bean
    public LocalContainerEntityManagerFactoryBean abstractEntityManagerFactoryBean(
            JpaVendorAdapter jpaVendorAdapter) {

        Properties properties = new Properties();
         properties.setProperty(FORMAT_SQL, String.valueOf(true));
        properties.setProperty(SHOW_SQL, String.valueOf(true));
        properties.setProperty(DIALECT, ModifiedSQLServerDialect.class.getTypeName());
        LocalContainerEntityManagerFactoryBean localContainerEntityManagerFactoryBean =
                new LocalContainerEntityManagerFactoryBean();

        localContainerEntityManagerFactoryBean.setDataSource(getDataSource());
        localContainerEntityManagerFactoryBean.setJpaVendorAdapter(jpaVendorAdapter);
        localContainerEntityManagerFactoryBean.setJpaProperties(properties);
        localContainerEntityManagerFactoryBean.setPackagesToScan("enteties");

        return localContainerEntityManagerFactoryBean;
    }


    @Bean
    public PlatformTransactionManager platformTransactionManager(EntityManagerFactory emf) {
        return new JpaTransactionManager(emf);
    }
}


public class ModifiedSQLServerDialect extends SQLServer2012Dialect {


    public ModifiedSQLServerDialect () {
        super();
        registerColumnType(Types.TIMESTAMP, "timestamp");
        registerColumnType(Types.DATE, "timestamp");
        registerColumnType(Types.TIME, "timestamp");
        registerHibernateType(Types.TIMESTAMP, "timestamp");
        registerHibernateType(Types.DATE, "timestamp");
        registerHibernateType(Types.TIME, "timestamp");
    }
}

但我仍然在 SQLServer 分析器中看到：

exec sp_executesql N'select datestbl0_.creationDate as creation1_0_0_ from DatesTbl datestbl0_ where datestbl0_.creationDate=@P0        ',N'@P0 `datetime2`','2018-12-26 08:10:40.0000003'

解决方案有什么问题？

Answer 1

我不认为使用DATETIME列作为 PK 是个好主意。 在同一纳秒内可能会创建两个实体，这两个实体会发生冲突。

您应该使用 IDENTITY 列或 SEQUENCE 并仅索引 DATETIME 列以加快查询速度。

这是一个遗留系统 - 我无法更改它。 主键由 2 个 int 字段和这个 datetime 列组成。

在这种情况下，您需要使用composite identifier 。

另外，我认为您不需要这些：

registerColumnType(Types.TIMESTAMP, "timestamp");
registerColumnType(Types.DATE, "timestamp");
registerColumnType(Types.TIME, "timestamp");

registerHibernateType(Types.TIMESTAMP, "timestamp");
registerHibernateType(Types.DATE, "timestamp");
registerHibernateType(Types.TIME, "timestamp");

SQL Server 方言应提供正确类型的映射。

Answer 2

解释

该问题与 mssql-jdbc（版本 4.x 和 6.x）中的一个问题有关， PreparedStatement.setTimestamp(index, timestamp, calendar) 存在数据类型转换问题，它始终将数据类型为datetime2的LocalDateTime参数发送到 SQL Server （忽略表的列类型）。 由于datetime （0.00333sec）和datetime2 （100 纳秒）的精度不同，并且使用datetime作为 PK，Hibernate 在这种情况下工作错误。

当我们运行主程序时， creationDate的值为2018-12-26 08:10:40.000000340 ，该值在数据库中保存为2018-12-26 08:10:40.000 ，因为 Hibernate 在数据库中找不到具有相同键的记录. 当我们再次运行主程序时，Hibernate 首先检查是否有具有相同键的记录，使用

'select datestbl0_.creationDate as creation1_0_0_ from DatesTbl datestbl0_ where datestbl0_.creationDate=@P0 ',N'@P0 'datetime2'','2018-12-26 08:10:40.0000003'

SQL Server似乎将表中的datetime值upcast为datetime2进行比较，没有返回记录。 因此 Hibernate 再次插入记录，并导致 Primary Key Violation。

解决方法

正如 Vlad Mihalcea 所建议的那样，将 DATETIME 列用作 PK 并不是一个好主意。
但是，假设我们仍然需要datetime列作为 PK，以下解决方法应该有效。 解决这个问题的关键是让datetime和datetime2比较返回true。 为此，我们可以在传递给 DB 之前将datetime2值截断/舍入为相应的datetime时间值。 以下对主程序的改动在SQL Server 2012 Express上测试无误。

public static void main(String[] args) {
    ApplicationContext context = new AnnotationConfigApplicationContext(Main.class);

    EntityManagerFactory entityManagerFactory = context.getBean(EntityManagerFactory.class);
    final EntityManager entityManager = entityManagerFactory.createEntityManager();

    LocalDateTime creationDate0 = LocalDateTime.of(2018, 12, 26, 8, 10, 40, 341340340);
    LocalDateTime creationDate3 = LocalDateTime.of(2018, 12, 26, 8, 10, 40, 343340340);
    LocalDateTime creationDate7 = LocalDateTime.of(2018, 12, 26, 8, 10, 40, 346670340);
    LocalDateTime creationDate10 = LocalDateTime.of(2018, 12, 26, 8, 10, 40, 349670340);
    entityManager.getTransaction().begin();
    final DatesTbl datesTbl0 = entityManager.merge(new DatesTbl(roundNanoSecForDateTime(creationDate0)));
    final DatesTbl datesTbl3 = entityManager.merge(new DatesTbl(roundNanoSecForDateTime(creationDate3)));
    final DatesTbl datesTbl7 = entityManager.merge(new DatesTbl(roundNanoSecForDateTime(creationDate7)));
    final DatesTbl datesTbl10 = entityManager.merge(new DatesTbl(roundNanoSecForDateTime(creationDate10)));
    entityManager.getTransaction().commit();
    System.out.println("test");
}

private static LocalDateTime roundNanoSecForDateTime(LocalDateTime localDateTime) {
    int nanoSec = localDateTime.getNano();
    // The rounding is based on following results on SQL server 2012 express
    // select cast(cast('2018-12-26 08:10:40.3414999' as datetime2) as datetime);
    // 2018-12-26 08:10:40.340
    // select cast(cast('2018-12-26 08:10:40.3415000' as datetime2) as datetime);
    // select cast(cast('2018-12-26 08:10:40.3444999' as datetime2) as datetime);
    // 2018-12-26 08:10:40.343
    // select cast(cast('2018-12-26 08:10:40.3445000' as datetime2) as datetime);
    // select cast(cast('2018-12-26 08:10:40.3484999' as datetime2) as datetime);
    // 2018-12-26 08:10:40.347
    // select cast(cast('2018-12-26 08:10:40.3485000' as datetime2) as datetime);
    // 2018-12-26 08:10:40.350
    int last7DigitOfNano = nanoSec - (nanoSec / 10000000) * 10000000;
    int roundedNanoSec = 0;
    if (last7DigitOfNano < 1500000) {
        roundedNanoSec = nanoSec - last7DigitOfNano;
    } else if (last7DigitOfNano < 4500000) {
        roundedNanoSec = nanoSec - last7DigitOfNano + 3000000;
    } else if (last7DigitOfNano < 8500000) {
        roundedNanoSec = nanoSec - last7DigitOfNano + 7000000;
    } else {
        roundedNanoSec = nanoSec - last7DigitOfNano + 10000000;
    }
    System.out.println("Before Rounding" + nanoSec);
    System.out.println("After Rounding" + roundedNanoSec);
    return localDateTime.withNano(roundedNanoSec);
}

参考：
1. SQL Server 中的 DateTime2 与 DateTime
2. 日期和时间数据类型和函数（Transact-SQL）