java - 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 how to do this in SQL for several DB platforms, but would like to know what database independent interfaces exist in java.sql to do this, and any input on people's experience with this across DB platforms.

Answer 1

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 2

ResultSet keys = statement.getGeneratedKeys();

Later, just iterate over ResultSet.

Answer 3

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 4

@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...)

Answer 5

@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).