How to Obtain Auto-Generated Keys With Hibernate

How to obtain auto-generated keys in a Hibernate - Spring Boot application.

Anghel Leonard

CORE ·

Sep. 16, 20 · Tutorial

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Consider the following Author entity that delegates the keys generation to the database system:

    Java
   
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@Entity public class Author implements Serializable { 
    
  @Id @GeneratedValue(strategy = GenerationType.IDENTITY) 
  private Long id; 
  
  private int age; 
  private String name; 
  private String genre; 
  ... 
}

Now, let's see how to retrieve the database auto-generated primary keys via getId(), JdbcTemplate and SimpleJdbcInsert.

Retrieve Auto-Generated Keys via getId()

In JPA style, retrieving the auto-generated keys can be done via getId() as in the following example:

    Java
   
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public void insertAuthorGetAutoGeneratedKeyViaGetId() {
  Author author = new Author(); 
  
  author.setAge(38); 
  author.setName("Alicia Tom"); 
  author.setGenre("Anthology"); 
  
  authorRepository.save(author); 
  
  long pk = author.getId(); 
  
  System.out.println("Auto generated key: " + pk); 
}

Retrieve Auto-Generated Keys via JdbcTemplate

Using JdbcTemplate to retrieve the auto-generated keys can be done via the update() method. This method comes in different flavors, but the signature needed here is:

public int update(PreparedStatementCreator ps,KeyHolder generatedKeyHolder) throws DataAccessException

The PreparedStatementCreator is a functional interface that takes an instance of java.sql.Connection and return a java.sql.PreparedStatement object. The KeyHolder object contains the auto-generated key returned by the update() method. In code lines:

    Java
   
 

     
    
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@Repository public class JdbcTemplateDao implements AuthorDao {
  
  private static final String SQL_INSERT
    = "INSERT INTO author (age, name, genre) VALUES (?, ?, ?);"; 
  
  private final JdbcTemplate jdbcTemplate; 
  
  public JdbcTemplateDao(JdbcTemplate jdbcTemplate) { 
    this.jdbcTemplate = jdbcTemplate; 
  } 
  
  @Override 
  @Transactional 
  public long insertAuthor(int age, String name, String genre) { 
    KeyHolder keyHolder = new GeneratedKeyHolder(); 
    jdbcTemplate.update(connection -> { 
      PreparedStatement ps = connection .prepareStatement(SQL_INSERT,
         Statement.RETURN_GENERATED_KEYS); 
      
      ps.setInt(1, age); 
      ps.setString(2, name); 
      ps.setString(3, genre); 
      
      return ps; 
    }, keyHolder); 
    
    return keyHolder.getKey().longValue(); 
  } 
}

In the above example, the PreparedStatement is instructed to return the auto-generated keys via Statement.RETURN_GENERATED_KEYS. Alternatively, the same thing can be accomplished as follows:

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// alternative 1 
PreparedStatement ps = connection .prepareStatement(SQL_INSERT, new String[]{"id"}); 
   
// alternative 2 
PreparedStatement ps = connection .prepareStatement(SQL_INSERT, new int[] {1});

Retrieve auto-generated keys via SimpleJdbcInsert

Consequently, calling SimpleJdbcInsert.executeAndReturnKey() method to insert a new record to author table and get back the auto-generated key:

    Java
   
 

     
    
x

            
          
@Repository 
public class SimpleJdbcInsertDao implements AuthorDao {
  private final SimpleJdbcInsert simpleJdbcInsert; 
  
  public SimpleJdbcInsertDao(DataSource dataSource) {
    this.simpleJdbcInsert = new SimpleJdbcInsert(dataSource) 
      .withTableName("author").usingGeneratedKeyColumns("id"); 
  }
  
  @Override
  @Transactional 
  public long insertAuthor(int age, String name, String genre) {
    return simpleJdbcInsert.executeAndReturnKey( 
      Map.of("age", age, "name", name, "genre", genre)).longValue(); 
  } 
}

The complete application is available on GitHub.

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