hibernate-demo/src/test/java/com/ankurm/hibernatedemo/testdb/DbCloseDelayTest.java

package com.ankurm.hibernatedemo.testdb;

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.jupiter.api.Assertions.assertThrows;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Backs docs/09-testing-in-memory-databases.md, chapter "What DB_CLOSE_DELAY=-1 actually does". Raw JDBC, no
 * Hibernate, to isolate exactly the H2-specific behaviour rather than anything the ORM layer
 * might paper over.
 */
class DbCloseDelayTest {

    private static final Logger DEMO = LoggerFactory.getLogger("DEMO");

    @Test
    void withoutCloseDelay_dataDisappearsWhenTheLastConnectionCloses() throws Exception {
        String url = "jdbc:h2:mem:no-close-delay-demo"; // no DB_CLOSE_DELAY at all
        try (Connection c1 = DriverManager.getConnection(url, "sa", "")) {
            try (Statement st = c1.createStatement()) {
                st.execute("create table t (id integer)");
                st.execute("insert into t values (1)");
            }
        } // c1 closes here -- this is H2's LAST open connection to this in-memory DB

        // A brand new connection to the SAME url now gets a BRAND NEW, EMPTY database --
        // querying the table we just created throws, because it no longer exists.
        try (Connection c2 = DriverManager.getConnection(url, "sa", "");
             Statement st = c2.createStatement()) {
            SQLException ex = assertThrows(SQLException.class, () -> st.execute("select * from t"));
            DEMO.info("without DB_CLOSE_DELAY=-1, reconnecting after the last close throws: {}: {}",
                    ex.getClass().getSimpleName(), ex.getMessage());
        }
    }

    @Test
    void withCloseDelayMinusOne_dataSurvivesAcrossConnectionCloses() throws Exception {
        String url = "jdbc:h2:mem:with-close-delay-demo;DB_CLOSE_DELAY=-1";
        try (Connection c1 = DriverManager.getConnection(url, "sa", "")) {
            try (Statement st = c1.createStatement()) {
                st.execute("create table t (id integer)");
                st.execute("insert into t values (1)");
            }
        } // c1 closes -- but DB_CLOSE_DELAY=-1 tells H2 to keep the in-memory DB alive anyway

        try (Connection c2 = DriverManager.getConnection(url, "sa", "");
             Statement st = c2.createStatement()) {
            var rs = st.executeQuery("select id from t");
            assertThat(rs.next()).isTrue();
            assertThat(rs.getInt(1)).isEqualTo(1);
            DEMO.info("with DB_CLOSE_DELAY=-1, reconnecting after the last close still sees the row inserted earlier");
        }
    }
}