Access to auto increment identity field after SQL insert in Java

Question

Any advice on how to read auto-incrementing identity field assigned to newly created record from call through java.sql.Statement.executeUpdate?

I know h

Answer 1

I've always had to make a second call using query after the insert.

You could use an ORM like hibernate. I think it does this stuff for you.

Answer 2

@ScArcher2

Making a second call is extremely dangerous. The process of INSERTing and selecting the resultant auto-generated keys must be atomic, otherwise you may receive inconsistent results on the key select. Consider two asynchronous INSERTs where they both complete before either has a chance to select the generated keys. Which process gets which list of keys? Most cross-database ORMs have to do annoying things like in-process thread locking in order to keep results deterministic. This is not something you want to do by hand, especially if you are using a database which does support atomic generated key retrieval (HSQLDB is the only one I know of which does not).

Answer 3

The following snibblet of code should do ya':

PreparedStatement stmt = conn.prepareStatement(sql, 
                                 Statement.RETURN_GENERATED_KEYS);
// ...

ResultSet res = stmt.getGeneratedKeys();
while (res.next())
    System.out.println("Generated key: " + res.getInt(1));

This is known to work on the following databases

• Derby
• MySQL
• SQL Server

For databases where it doesn't work (HSQLDB, Oracle, PostgreSQL, etc), you will need to futz with database-specific tricks. For example, on PostgreSQL you would make a call to SELECT NEXTVAL(...) for the sequence in question.

Note that the parameters for executeUpdate(...) are analogous.

Answer 4

ResultSet keys = statement.getGeneratedKeys();

Later, just iterate over ResultSet.

Answer 5

@ScArcher2 : I agree, Hibernate needs to make a second call to get the newly generated identity UNLESS an advanced generator strategy is used (sequence, hilo...)