将Cassandra BoundStatement的ResultSet映射/转换/转换为使用Object-mapping API构建的Java classe的最有效方法是什么？ [英] What is the most efficient way to map/transform/cast a Cassandra BoundStatement's ResultSet to a Java classe built using the Object-mapping API?

问题描述

DataStax Java中是否存在用于Apache Cassandra的内置方法，将来自BoundStatement的ResultSet映射到使用Object-mapping API构建的域对象Java类？

<我是一个从Mapper + Accessor方法转向BoundStatement方法的新手，并希望继续使用使用Object-mapping API构建的域对象的Java类，这样我在转到我的DAO方法的实现时做了很小的改动。 BoundStatement。我希望以通用方式执行此操作，并避免迭代每个ResultSet行并为每个域对象逐个执行row.get。

使用时Mapper + Accessor方法，Result.all（）做得非常好。找不到类似于BoundStatement方法的任何内容。

谢谢

IPVP

解决方案

您可以完成将 ResultSet 映射到 com.datastax.driver.mapping.Result 通过为您的对象实例化 Mapper ，然后使用 Mapper.map 。这是一个例子，取自 java驱动程序的测试从定期执行的查询中获取 ResultSet 并将其映射到结果< Post> ，然后迭代结果以访问每个映射的帖子：

  MappingManager manager = new MappingManager（session）; 
 
 Mapper< Post> m = manager.mapper（Post.class）; 
 ... 
 //使用仅检索某些字段的投影查询检索帖子
 ResultSet rs = session.execute（select user_id，post_id，title from user_id = + u1.getUserId（））; 
 
结果<发布> result = m.map（rs）; 
 for（帖子：结果）{
 assertThat（post.getUserId（））。isEqualTo（u1.getUserId（））; 
 assertThat（post.getPostId（））。isNotNull（）; 
 assertThat（post.getTitle（））。isNotNull（）; 
 
 assertThat（post.getDevice（））。isNull（）; 
 assertThat（post.getTags（））。isNull（）; 
} 
  

Is there a builtin way in DataStax Java for Apache Cassandra to map the ResultSet coming from a BoundStatement to the domain objects Java classes built with using the Object-mapping API?

I am a newbie moving from the Mapper + Accessor approach to BoundStatement approach and would like to continue using the domain objects' Java classes built with the Object-mapping API so I do minimal changes to the implementation of my DAO methods while moving to the BoundStatement. I am looking to do it in a generic way and avoid to iterate over each ResultSet row and do a row.get one by one for each domain object.

While using the Mapper + Accessor approach, the Result.all() do that very well. Could not find anything similar to the BoundStatement approach.

Thanks

IPVP

解决方案

You can accomplish mapping a ResultSet to a com.datastax.driver.mapping.Result by instantiating a Mapper for your object, and then using Mapper.map. Here is an example, taken from the java driver's tests that takes a ResultSet from a regularly executed query and maps it to a Result<Post>, and then iterates over the Result to access each mapped Post:

MappingManager manager = new MappingManager(session);

Mapper<Post> m = manager.mapper(Post.class);
...
// Retrieve posts with a projection query that only retrieves some of the fields
ResultSet rs = session.execute("select user_id, post_id, title from posts where user_id = " + u1.getUserId());

Result<Post> result = m.map(rs);
for (Post post : result) {
    assertThat(post.getUserId()).isEqualTo(u1.getUserId());
    assertThat(post.getPostId()).isNotNull();
    assertThat(post.getTitle()).isNotNull();

    assertThat(post.getDevice()).isNull();
    assertThat(post.getTags()).isNull();
}

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