Update Event API

- Adjust OrderPlacedEvent to only construct the order
- Introduce ProductAddedEvent to be able to add several products
to a order
- Introduce ProductCountIncrementedEvent to increase the number of
product instances for a given Order
- Introduce ProductCountDecrementedEvent to increase the number of
product instances for a given Order
- Introduce ProductRemovedEvent to signal whenever all the product count
 drops below 1

#BAEL-4767

axon/src/main/java/com/baeldung/axon/coreapi/events/OrderPlacedEvent.java

@@ -5,44 +5,36 @@ import java.util.Objects;
 public class OrderPlacedEvent {
 
     private final String orderId;
-    private final String product;
 
-    public OrderPlacedEvent(String orderId, String product) {
+    public OrderPlacedEvent(String orderId) {
         this.orderId = orderId;
-        this.product = product;
     }
 
     public String getOrderId() {
         return orderId;
     }
 
-    public String getProduct() {
+    @Override
-        return product;
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        OrderPlacedEvent that = (OrderPlacedEvent) o;
+        return Objects.equals(orderId, that.orderId);
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(orderId, product);
+        return Objects.hash(orderId);
-    }
-
-    @Override
-    public boolean equals(Object obj) {
-        if (this == obj) {
-            return true;
-        }
-        if (obj == null || getClass() != obj.getClass()) {
-            return false;
-        }
-        final OrderPlacedEvent other = (OrderPlacedEvent) obj;
-        return Objects.equals(this.orderId, other.orderId)
-                && Objects.equals(this.product, other.product);
     }
 
     @Override
     public String toString() {
         return "OrderPlacedEvent{" +
                 "orderId='" + orderId + '\'' +
-                ", product='" + product + '\'' +
                 '}';
     }
 }

axon/src/main/java/com/baeldung/axon/coreapi/events/ProductAddedEvent.java

@@ -0,0 +1,47 @@
+package com.baeldung.axon.coreapi.events;
+
+import java.util.Objects;
+
+public class ProductAddedEvent {
+
+    private final String orderId;
+    private final String productId;
+
+    public ProductAddedEvent(String orderId, String productId) {
+        this.orderId = orderId;
+        this.productId = productId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public String getProductId() {
+        return productId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        ProductAddedEvent that = (ProductAddedEvent) o;
+        return Objects.equals(orderId, that.orderId) && Objects.equals(productId, that.productId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId, productId);
+    }
+
+    @Override
+    public String toString() {
+        return "ProductAddedEvent{" +
+                "orderId='" + orderId + '\'' +
+                ", productId='" + productId + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/events/ProductCountDecrementedEvent.java

@@ -0,0 +1,47 @@
+package com.baeldung.axon.coreapi.events;
+
+import java.util.Objects;
+
+public class ProductCountDecrementedEvent {
+
+    private final String orderId;
+    private final String productId;
+
+    public ProductCountDecrementedEvent(String orderId, String productId) {
+        this.orderId = orderId;
+        this.productId = productId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public String getProductId() {
+        return productId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        ProductCountDecrementedEvent that = (ProductCountDecrementedEvent) o;
+        return Objects.equals(orderId, that.orderId) && Objects.equals(productId, that.productId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId, productId);
+    }
+
+    @Override
+    public String toString() {
+        return "ProductCountDecrementedEvent{" +
+                "orderId='" + orderId + '\'' +
+                ", productId='" + productId + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/events/ProductCountIncrementedEvent.java

@@ -0,0 +1,47 @@
+package com.baeldung.axon.coreapi.events;
+
+import java.util.Objects;
+
+public class ProductCountIncrementedEvent {
+
+    private final String orderId;
+    private final String productId;
+
+    public ProductCountIncrementedEvent(String orderId, String productId) {
+        this.orderId = orderId;
+        this.productId = productId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public String getProductId() {
+        return productId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        ProductCountIncrementedEvent that = (ProductCountIncrementedEvent) o;
+        return Objects.equals(orderId, that.orderId) && Objects.equals(productId, that.productId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId, productId);
+    }
+
+    @Override
+    public String toString() {
+        return "ProductCountIncrementedEvent{" +
+                "orderId='" + orderId + '\'' +
+                ", productId='" + productId + '\'' +
+                '}';
+    }
+}

axon/src/main/java/com/baeldung/axon/coreapi/events/ProductRemovedEvent.java

@@ -0,0 +1,47 @@
+package com.baeldung.axon.coreapi.events;
+
+import java.util.Objects;
+
+public class ProductRemovedEvent {
+
+    private final String orderId;
+    private final String productId;
+
+    public ProductRemovedEvent(String orderId, String productId) {
+        this.orderId = orderId;
+        this.productId = productId;
+    }
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public String getProductId() {
+        return productId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        ProductRemovedEvent that = (ProductRemovedEvent) o;
+        return Objects.equals(orderId, that.orderId) && Objects.equals(productId, that.productId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(orderId, productId);
+    }
+
+    @Override
+    public String toString() {
+        return "ProductRemovedEvent{" +
+                "orderId='" + orderId + '\'' +
+                ", productId='" + productId + '\'' +
+                '}';
+    }
+}