feat: 订单支持优惠金额字段，优先使用优惠金额

src/main/java/com/example/building/dto/CreateOrderRequest.java

@@ -30,10 +30,15 @@ public class CreateOrderRequest {
     private List<OrderItemDTO> items;
 
     /**
-     * 折扣率(百分比), 默认100
+     * 折扣率(百分比), 默认100（保留此逻辑）
      */
     private BigDecimal discountRate;
 
+    /**
+     * 优惠金额(元)
+     */
+    private BigDecimal discountMoney;
+
     /**
      * 备注
      */

src/main/java/com/example/building/entity/Order.java

@@ -57,6 +57,11 @@ public class Order {
      */
     private BigDecimal discountAmount;
 
+    /**
+     * 优惠金额(元，用户输入)
+     */
+    private BigDecimal discountMoney;
+
     /**
      * 实收金额
      * 计算公式: totalAmount - discountAmount
@@ -64,7 +69,7 @@ public class Order {
     private BigDecimal actualAmount;
 
     /**
-     * 折扣率(百分比)
+     * 折扣率(百分比，保留此逻辑)
      */
     private BigDecimal discountRate;
 

src/main/java/com/example/building/service/impl/OrderServiceImpl.java

@@ -117,9 +117,21 @@ public class OrderServiceImpl implements OrderService {
         order.setTotalAmount(totalAmount);
 
         // 5. 计算优惠金额和实付金额
+        BigDecimal discountAmount;
         BigDecimal discountRate = order.getDiscountRate();
-        BigDecimal discountAmount = totalAmount.multiply(new BigDecimal("100").subtract(discountRate))
+        BigDecimal discountMoney = request.getDiscountMoney();
-                .divide(new BigDecimal("100"), 2, RoundingMode.HALF_UP);
+        
+        // 优先使用优惠金额，如果没有填则用折扣率计算
+        if (discountMoney != null && discountMoney.compareTo(BigDecimal.ZERO) > 0) {
+            discountAmount = discountMoney;
+        } else {
+            // 折扣率默认100，即不打折
+            if (discountRate == null) {
+                discountRate = new BigDecimal("100");
+            }
+            discountAmount = totalAmount.multiply(new BigDecimal("100").subtract(discountRate))
+                    .divide(new BigDecimal("100"), 2, RoundingMode.HALF_UP);
+        }
         BigDecimal actualAmount = totalAmount.subtract(discountAmount);
 
         order.setDiscountAmount(discountAmount);
@@ -342,9 +354,20 @@ public class OrderServiceImpl implements OrderService {
         
         order.setTotalAmount(totalAmount);
         
+        BigDecimal discountAmount;
         BigDecimal discountRate = order.getDiscountRate();
-        BigDecimal discountAmount = totalAmount.multiply(new BigDecimal("100").subtract(discountRate))
+        BigDecimal discountMoney = order.getDiscountMoney();
-                .divide(new BigDecimal("100"), 2, RoundingMode.HALF_UP);
+        
+        // 优先使用优惠金额，如果没有填则用折扣率计算
+        if (discountMoney != null && discountMoney.compareTo(BigDecimal.ZERO) > 0) {
+            discountAmount = discountMoney;
+        } else {
+            if (discountRate == null) {
+                discountRate = new BigDecimal("100");
+            }
+            discountAmount = totalAmount.multiply(new BigDecimal("100").subtract(discountRate))
+                    .divide(new BigDecimal("100"), 2, RoundingMode.HALF_UP);
+        }
         BigDecimal actualAmount = totalAmount.subtract(discountAmount);
         
         order.setDiscountAmount(discountAmount);