implementation bael-6949 (#15643)

* implementation

* feedbacks

---------

Co-authored-by: technoddy <mail.technoddy@gmail.com>

persistence-modules/core-java-persistence-3/pom.xml

@@ -6,6 +6,18 @@
     <artifactId>core-java-persistence-3</artifactId>
     <version>0.1.0-SNAPSHOT</version>
     <name>core-java-persistence-3</name>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>17</source>
+                    <target>17</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
     <packaging>jar</packaging>
 
     <parent>

persistence-modules/core-java-persistence-3/src/main/java/jdbcpagination/PaginationLogic.java

@@ -0,0 +1,33 @@
+package jdbcpagination;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+
+public class PaginationLogic {
+
+    public static ResultSet readPageWithLimitAndOffset(Connection connection, int offset, int pageSize) throws SQLException {
+        String sql = """
+             SELECT * FROM employees
+             LIMIT ? OFFSET ?
+            """;
+        PreparedStatement preparedStatement = connection.prepareStatement(sql);
+        preparedStatement.setInt(1, pageSize);
+        preparedStatement.setInt(2, offset);
+
+        return preparedStatement.executeQuery();
+    }
+
+    public static ResultSet readPageWithSortedKeys(Connection connection, int lastFetchedId, int pageSize) throws SQLException {
+        String sql = """
+             SELECT * FROM employees
+             WHERE id > ? LIMIT ?
+            """;
+        PreparedStatement preparedStatement = connection.prepareStatement(sql);
+        preparedStatement.setInt(1, lastFetchedId);
+        preparedStatement.setInt(2, pageSize);
+
+        return preparedStatement.executeQuery();
+    }
+}

persistence-modules/core-java-persistence-3/src/test/java/jdbcpagination/PaginationLogicUnitTest.java

@@ -0,0 +1,134 @@
+package jdbcpagination;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.IntStream;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class PaginationLogicUnitTest {
+    private static Connection connection = null;
+    private static final String JDBC_URL = "jdbc:h2:mem:testDB";
+    private static final String USERNAME = "dbUser";
+    private static final String PASSWORD = "dbPassword";
+
+    @BeforeAll
+    public static void setup() throws Exception {
+        connection = connect(JDBC_URL, USERNAME, PASSWORD);
+        populateDB();
+    }
+
+    @AfterAll
+    public static void tearDown() throws SQLException {
+        destroyDB();
+    }
+
+    @Test
+    public void givenDBPopulated_WhenReadPaginatedWithLimitAndOffset_ThenReturnsPaginatedResult() throws SQLException {
+        int offset = 0;  // offset is set to 0 and keep updating with pageSize
+        int pageSize = 100_000;
+        int totalPages = 0;
+        while (true) {
+            ResultSet resultSet = PaginationLogic.readPageWithLimitAndOffset(connection, offset, pageSize);
+            if (!resultSet.next())
+                break;
+            List<String> resultPage = new ArrayList<>();
+
+            do {
+                resultPage.add(resultSet.getString("first_name"));
+            } while (resultSet.next());
+            assertEquals("firstname" + (resultPage.size() * (totalPages + 1)), resultPage.get(resultPage.size() - 1));
+            offset += pageSize;
+            totalPages++;
+        }
+        assertEquals(10, totalPages);
+    }
+
+    @Test
+    public void givenDBPopulated_WhenReadPaginatedWithSortedKeys_ThenReturnsPaginatedResult() throws SQLException {
+        // find min and max ID
+        PreparedStatement preparedStatement = connection.prepareStatement("SELECT min(id) as min_id, max(id) as max_id FROM employees");
+        ResultSet resultSet = preparedStatement.executeQuery();
+        resultSet.next();
+
+        int minId = resultSet.getInt("min_id");
+        int maxId = resultSet.getInt("max_id");
+        int lastFetchedId = 0; // assign lastFetchedId to minId
+
+        int pageSize = 100_000;
+        int totalPages = 0;
+
+        while ((lastFetchedId + pageSize) <= maxId) {
+            resultSet = PaginationLogic.readPageWithSortedKeys(connection, lastFetchedId, pageSize);
+            if (!resultSet.next())
+                break;
+            List<String> resultPage = new ArrayList<>();
+            do {
+                resultPage.add(resultSet.getString("first_name"));
+                lastFetchedId = resultSet.getInt("id");
+            } while (resultSet.next());
+            assertEquals("firstname" + (resultPage.size() * (totalPages + 1)), resultPage.get(resultPage.size() - 1));
+            totalPages++;
+        }
+        assertEquals(10, totalPages);
+    }
+
+    private static void destroyDB() throws SQLException {
+        String destroy = """
+              DROP table IF EXISTS EMPLOYEES;
+            """;
+        connection.prepareStatement(destroy)
+            .execute();
+    }
+
+    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();
+
+        String load = """
+            INSERT INTO EMPLOYEES (first_name, last_name, salary)
+            VALUES(?,?,?)
+            """;
+        IntStream.rangeClosed(1, 1_000_000)
+            .forEach(i -> {
+                PreparedStatement preparedStatement1 = null;
+                try {
+                    preparedStatement1 = connection.prepareStatement(load);
+                    preparedStatement1.setString(1, "firstname" + i);
+                    preparedStatement1.setString(2, "lastname" + i);
+                    preparedStatement1.setDouble(3, 100_000 + (1_000_000 - 100_000) + Math.random());
+
+                    preparedStatement1.execute();
+                } catch (SQLException e) {
+                    throw new RuntimeException(e);
+                }
+            });
+    }
+
+    public static Connection connect(String url, String user, String password) throws SQLException {
+        Connection connection = DriverManager.getConnection(url, user, password);
+        if (connection != null) {
+            System.out.println("Connected to database");
+        }
+
+        return connection;
+    }
+
+}