provide an initial implementation - not tested (iluwatar#79)

active-record/src/main/java/com/iluwatar/activerecord/Customer.java

@@ -1,37 +1,38 @@
 package com.iluwatar.activerecord;
 
+import java.sql.ResultSet;
 import java.util.List;
-import lombok.EqualsAndHashCode;
+import javax.sql.DataSource;
 import lombok.Getter;
-import lombok.RequiredArgsConstructor;
 import lombok.Setter;
 
 @Getter
 @Setter
-@RequiredArgsConstructor
-@EqualsAndHashCode(onlyExplicitlyIncluded = true)
-public class Customer {
+public class Customer extends RecordBase {
 
   private Long id;
   private String customerNumber;
   private String firstName;
   private String lastName;
   private List<Order> orders;
 
-  public Customer findById(Long id) {
-    return new Customer();
+  public Customer(DataSource dataSource) {
+    super(dataSource);
   }
 
   public Customer findByNumber(String customerNumber) {
-    return new Customer();
+    // TODO
+    return null;
+//    return new Customer();
   }
 
-  public List<Customer> findAll() {
-    return List.of();
+  @Override
+  protected String getTableName() {
+    return "customer";
   }
 
-  public void save(Customer customer) {
+  @Override
+  protected void setFieldsFromResultSet(ResultSet rs) {
 
   }
-
 }

active-record/src/main/java/com/iluwatar/activerecord/RecordBase.java

@@ -1,5 +1,12 @@
 package com.iluwatar.activerecord;
 
+import java.lang.reflect.InvocationTargetException;
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.List;
 import javax.sql.DataSource;
 import lombok.RequiredArgsConstructor;
 
@@ -8,4 +15,78 @@ public abstract class RecordBase {
 
   private final DataSource dataSource;
 
+  protected Connection getConnection() throws SQLException {
+    return dataSource.getConnection();
+  }
+
+  /**
+   * Returns an underlying table name defined within the domain model.
+   *
+   * @return the table name.
+   */
+  protected abstract String getTableName();
+
+  protected abstract void setFieldsFromResultSet(ResultSet rs);
+
+  public <T extends RecordBase> List<T> findAll(Class<T> clazz) {
+    List<T> recordList = new ArrayList<>();
+    try (Connection conn = getConnection();
+        PreparedStatement pstmt = conn.prepareStatement(constructGetByIdQuery(clazz))) {
+      try (ResultSet rs = pstmt.executeQuery()) {
+        while (rs.next()) {
+          T record = getDeclaredClassInstance(clazz);
+          record.setFieldsFromResultSet(rs);
+          recordList.add(record);
+        }
+        return recordList;
+      }
+    } catch (SQLException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /**
+   * Find a domain model by its ID.
+   *
+   * @param id    domain model identifier.
+   * @param clazz domain model class.
+   * @param <T>   domain model type.
+   * @return the domain model.
+   */
+  public <T extends RecordBase> T findById(Long id, Class<T> clazz) {
+    try (Connection conn = getConnection();
+        PreparedStatement pstmt = conn.prepareStatement(constructGetByIdQuery(clazz))) {
+      pstmt.setLong(1, id);
+      try (ResultSet rs = pstmt.executeQuery()) {
+        if (rs.next()) {
+          T record = getDeclaredClassInstance(clazz);
+          record.setFieldsFromResultSet(rs);
+          return record;
+        }
+        return getDeclaredClassInstance(clazz);
+      }
+    } catch (SQLException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  public void save() {
+    // TODO
+  }
+
+  private <T extends RecordBase> String constructGetByIdQuery(Class<T> clazz) {
+    return "SELECT * FROM " + getDeclaredClassInstance(clazz).getTableName()
+        + " WHERE id = ?";
+  }
+
+  private <T extends RecordBase> T getDeclaredClassInstance(Class<T> clazz) {
+    try {
+      return clazz.getDeclaredConstructor().newInstance();
+    } catch (InvocationTargetException | NoSuchMethodException | IllegalAccessException |
+             InstantiationException e) {
+      throw new IllegalStateException(
+          "Unable to create a new instance of the class=" + clazz.getName(), e);
+    }
+  }
+
 }