Getting the Insert ID in JDBC

1. Introduction

When working with JDBC to insert data into a database, retrieving the auto-generated primary key is a common requirement. JDBC provides a mechanism to fetch the insert ID immediately after an insert operation.

This tutorial discusses how to get the insert ID immediately after an insert operation.

2. Setup

Before discussing and implementing logic to get the insert ID, we’ll first discuss the necessary setup steps.

To test our implementation, we’ll use an in-memory H2 database. We can add the h2 database dependency in the pom.xml file:

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>2.1.214</version>
</dependency>

In our test setup, we can connect to the H2 database and populate the database with our sample table, i.e., the Employees table.

private static void populateDB() throws SQLException {
    String createTable = """
        CREATE TABLE EMPLOYEES (
            id SERIAL PRIMARY KEY ,
            first_name VARCHAR(50),
            last_name VARCHAR(50),
            salary DECIMAL(10, 2)
        );
        """;
    PreparedStatement preparedStatement = connection.prepareStatement(createTable);
    preparedStatement.execute();
}

3. Retrieving Insert IDs

When executing the insert statement, if the table has an auto-generated key (such as AUTO_INCREMENT in MySQL, a SERIAL in PostgreSQL, or IDENTITY in the H2 database), JDBC can retrieve these keys using the getGeneratedKeys() method.

For inserting a record, we can use preparedStatement.executeUpdate() which returns the number of rows updated. To fetch the insert IDs we can use Statement.RETURN_GENERATED_KEYS:

String sql = "INSERT INTO employees (first_name, last_name, salary) VALUES (?, ?, ?)";
PreparedStatement statement = connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
statement.setString(1, "first");
statement.setString(2, "last");
statement.setDouble(3, 100.0);
int numRows = statement.executeUpdate();

Now, we can call statement.getGeneratedKeys() to get the ResultSet, which allows us to fetch the inserted IDs using getLong():

ResultSet generatedKeys = statement.getGeneratedKeys();
List<Long> insertIds = new ArrayList<>();
while(generatedKeys.next()){
    insertIds.add(generatedKeys.getLong(1));
 }

In the above code, getLong(1) retrieves the first generated key from ResultSet. If the insert operation produces multiple generated keys, we can access them using their respective positions. For instance, getLong(2) would fetch the second generated key in the row, getLong(3) would generate get third, and so on. Additionally, we can also access the generated keys with column labels, for example, getLong(“id1”), getLong(“id2”), and so on.

We can verify the result by writing a unit test:

@Test
public void givenDBPopulated_WhenGetInsertIds_ThenReturnsIds() throws SQLException {
    GetInsertIds getInsertIds = new GetInsertIds();
    List<Long> actualIds = getInsertIds.insertAndReturnIds(connection);
    ResultSet resultSet = connection.prepareStatement("select id from employees").executeQuery();
    List<Long> expectedIds = new ArrayList<>();
    while (resultSet.next()){
        expectedIds.add(resultSet.getLong(1));
    }
    assertEquals(expectedIds, actualIds);
}

4. Conclusion

In this article, we discuss the mechanism to get the insert IDs of inserted records using JDBC PreparedStatement. We also implemented the logic and verified it using a unit test.

As usual, the complete source code for the examples is available over on GitHub.