java - @SingleValueResult は何をしますか?

Question

何をし@SingleValueResultますか？「単一値の結果」という制約を課しますか?

フルネーム：org.skife.jdbi.v2.sqlobject.customizers.SingleValueResult

これに関するいくつかのリンクを次に示します。

• https://groups.google.com/forum/#!topic/jdbi/tQge_FNUoiw
• https://news.ycombinator.com/item?id=8134591

Answer 1

No, it doesn't.

Instead it just provides some more type information for Optional or Maybe return types.

When JDBI recognizes that only a single row will be needed from the database, it will tell the database that only one row will be needed (see addStatementCustomizer(StatementCustomizers.MAX_ROW_ONE) in the Query class).

This will let the database optimize the returned data. But your Java application will never know if there was ever a second row.