如何将sql DATE映射到LocalDate [英] How to map sql DATE to LocalDate

问题描述

我想在 DATE 列中存储 LocalDate 并保持不变。根据定义， DATE 和 LocalDate 都是本地类型。因此， timezone 的概念不应以任何方式干扰。

I want to store a LocalDate in a DATE column and retrieve it unchanged. Both DATE and LocalDate are "local" types by definition. Therefore, the concept of timezone should not interfere in any way.

下面的代码是创建一个<$的表的最小示例c $ c> DATE 内存数据库中的列。 maven工件 com.h2database：h2：1.4.192 必须在类路径中。

The code below is a minimal example that creates a table with a DATE column in a in-memory database. The maven artifact com.h2database:h2:1.4.192 must be in the classpath.

首先，定义方法 insert 和 retrieve ：

static void insert(DataSource ds, String date) throws SQLException {
  try (Connection conn = ds.getConnection();
       Statement stmt = conn.createStatement()) {
    stmt.execute("CREATE TABLE people (id BIGINT NOT NULL AUTO_INCREMENT"
      + ", born DATE NOT NULL, PRIMARY KEY (id) );");
    stmt.execute("INSERT INTO people (born) VALUES ('" + date + "')");
  }
}

static LocalDate retrieve(DataSource ds) throws SQLException {
  try (Connection conn = ds.getConnection();
       Statement stmt = conn.createStatement();
       ResultSet rs = stmt.executeQuery("SELECT * FROM people limit 1")) {
    if (rs.next()) {
      java.sql.Date retrieved = java.sql.Date.valueOf(rs.getString("born"));
      return retrieved.toLocalDate();
    }
    throw new IllegalStateException("No data");
  }
}

请注意插入方法在单引号中使用 LocalDate 的 toString 值，因此Java没有机会™创造时区歧义。现在调用插入一次，然后多次检索，每次使用不同的timzone设置：

Notice that the insert method uses the toString value of the LocalDate in single quotes, so there's no opportunity for Java™ to create timezone ambiguity. Now call insert once and then several times retrieve, with different timzone settings each time:

public static void main(String[] args) throws Exception {
  DataSource ds = JdbcConnectionPool.create("jdbc:h2:mem:test", "sa", "sa");
  LocalDate born = LocalDate.parse("2015-05-20");
  insert(ds, born.toString());
  System.out.println("Inserted:  " + born);
  for (int i : new int[]{-14, 0, 12}) {
    TimeZone z = TimeZone.getTimeZone(String.format("Etc/GMT%+02d", i));
    TimeZone.setDefault(z);
    System.out.println("Retrieved: " + retrieve(ds));
  }
}

然后打印以下内容：

Inserted:  2015-05-20
Retrieved: 2015-05-20
Retrieved: 2015-05-19
Retrieved: 2015-05-18

如何编写检索方法，以便假设数据库表没有改变，它返回与无条件相同的值？

How to write the retrieve method so that it returns the same value that was inserted unconditionally, assuming that the database table doesn't change?

推荐答案

<我只是尝试对你的检索方法进行以下修改，它对我有用：

I just tried the following modification to your retrieve method and it worked for me:

DATE类型的H2文档表示它是

日期数据类型。格式是yyyy-MM-dd。

The date data type. The format is yyyy-MM-dd.

所以，而不是你的......

So, instead of your ...

java.sql.Date retrieved = (java.sql.Date) rs.getObject("born");
return retrieved.toLocalDate();

...我刚刚使用过......

... I just used ...

return LocalDate.parse(rs.getString("born"));

...我的代码已生成

... and my code produced

Inserted:  2015-05-20
Retrieved: 2015-05-20
Retrieved: 2015-05-20
Retrieved: 2015-05-20

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