Initial commit: backend code

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

@@ -0,0 +1,61 @@
+package com.example.building.entity;
+
+import com.baomidou.mybatisplus.annotation.*;
+import lombok.Data;
+
+import java.math.BigDecimal;
+import java.time.LocalDateTime;
+
+/**
+ * 订单明细实体类
+ */
+@Data
+@TableName("order_items")
+public class OrderItem {
+
+    @TableId(type = IdType.ASSIGN_UUID)
+    private String itemId;
+
+    /**
+     * 订单ID
+     */
+    private String orderId;
+
+    /**
+     * 商品ID
+     */
+    private String productId;
+
+    /**
+     * 商品名称(冗余)
+     */
+    private String productName;
+
+    /**
+     * 商品规格(冗余)
+     */
+    private String productSpec;
+
+    /**
+     * 单位(冗余)
+     */
+    private String unit;
+
+    /**
+     * 销售单价(当时标价)
+     */
+    private BigDecimal price;
+
+    /**
+     * 数量
+     */
+    private Integer quantity;
+
+    /**
+     * 小计(单价×数量)
+     */
+    private BigDecimal subtotal;
+
+    @TableField(fill = FieldFill.INSERT)
+    private LocalDateTime createdAt;
+}