add comments for equals & hashCode

Author: vincentlauvlwj

ktorm-core/src/main/kotlin/org/ktorm/entity/Entity.kt

@@ -44,11 +44,11 @@ import kotlin.reflect.jvm.jvmErasure
  *
  * ### Creating Entity Objects
  *
- * As everyone knows, interfaces cannot be instantiated, so Ktorm provides [Entity.create] functions for us to
- * create entity objects. Those functions generate implementations for entity interfaces via JDK dynamic proxy
+ * As everyone knows, interfaces cannot be instantiated, so Ktorm provides a [Entity.create] function for us to
+ * create entity objects. This function generate implementations for entity interfaces via JDK dynamic proxy
  * and create their instances.
  *
- * If you don't like creating objects by [Entity.create] functions, Ktorm also provides an abstract factory class
+ * In case you don't like creating objects by [Entity.create], Ktorm also provides an abstract factory class
  * [Entity.Factory]. This class overloads the `invoke` operator of Kotlin, so we just need to add a companion
  * object to our entity class extending from [Entity.Factory], then entity objects can be created just like there
  * is a constructor: `val department = Department()`.
@@ -209,6 +209,27 @@ public interface Entity<E : Entity<E>> : Serializable {
      */
     public fun copy(): E
 
+    /**
+     * Indicate whether some other object is "equal to" this entity.
+     * Two entities are equal only if they have the same [entityClass] and [properties].
+     *
+     * @since 3.4.0
+     */
+    public override fun equals(other: Any?): Boolean
+
+    /**
+     * Return a hash code value for this entity.
+     *
+     * @since 3.4.0
+     */
+    public override fun hashCode(): Int
+
+    /**
+     * Return a string representation of this table.
+     * The format is like `Employee{id=1, name=Eric, job=contributor, hireDate=2021-05-05, salary=50}`.
+     */
+    public override fun toString(): String
+
     /**
      * Companion object provides functions to create entity instances.
      */

ktorm-core/src/test/kotlin/org/ktorm/entity/EntityTest.kt

@@ -520,7 +520,8 @@ class EntityTest : BaseTest() {
         val employee = database.employees.find { it.id eq 2 } ?: return
         val copy = employee.copy()
 
-        assert(employee.hireDate == copy.hireDate)
+        assert(employee == copy)
+        assert(employee !== copy)
         assert(employee.hireDate !== copy.hireDate) // should not be the same instance because of deep copy.
         assert(copy.manager?.implementation?.parent === copy.implementation) // should keep the parent relationship.
     }