使用JDBI SQL Object API同时检索或创建新行

Question

I'm using JDBI and would like to use the SQL Object API in order to, given a field value, search if a row exists for this value, return its key if found, create it if not found and return the generated key (talking to a MySQL database).

Is it possible to do this using SQL Object API without any stored procedure?

Answer 1

There is no magic in the JDBI SQL Object API whch will do this for you. You will need several SQL statements, just as you would in a stored procedure.

If you want to combine it in a single method in your DAO class, you can make it an abstract class rather than an interface, then it can have a concrete method containing the logic you need, and annotate that to make it occur within a transaction:

  public abstract class MyDAO {

    @Transaction
    public long getId(String value) {
      Thing thing = findByValue(value);
      if (thing != null) {
        return thing.getId();
      } else {
        return addNewRecord(value);
      } 

    }

    @SqlQuery("select * from mytable where value = :value")
    public Thing findByValue(@Bind("value") String value);

    @SqlUpdate("insert into mytable (value) values (:value)")
    @GetGeneratedKeys
    public long addNewRecord(String value);

  }

Answer 2

To do this correctly, you need to handle the concurrency inside the database. Create the table where value is a unique index:

CREATE TABLE mytable (
  id bigint NOT NULL PRIMARY KEY,
  value varchar(100) NOT NULL UNIQUE
);

You can then use MySQL's INSERT IGNORE syntax, which skips errors such as duplicate keys:

INSERT IGNORE INTO mytable VALUES (:value);

After the insert, read the row:

SELECT * FROM mytable WHERE value = :value;

If always running the extra insert is a performance concern, you can perform the read first and only insert if the record does not exist.