fix: validate role code uniqueness before insert

src/Application/TakeoutSaaS.Application/Identity/Handlers/CreateRoleCommandHandler.cs

@@ -3,6 +3,8 @@ using TakeoutSaaS.Application.Identity.Commands;
 using TakeoutSaaS.Application.Identity.Contracts;
 using TakeoutSaaS.Domain.Identity.Entities;
 using TakeoutSaaS.Domain.Identity.Repositories;
+using TakeoutSaaS.Shared.Abstractions.Constants;
+using TakeoutSaaS.Shared.Abstractions.Exceptions;
 using TakeoutSaaS.Shared.Abstractions.Tenancy;
 
 namespace TakeoutSaaS.Application.Identity.Handlers;
@@ -20,20 +22,34 @@ public sealed class CreateRoleCommandHandler(
         // 1. 获取租户上下文
         var tenantId = request.TenantId ?? tenantProvider.GetCurrentTenantId();
 
-        // 2. 构建角色实体
+        // 2. 归一化输入并校验唯一
+        var name = request.Name?.Trim() ?? string.Empty;
+        var code = request.Code?.Trim() ?? string.Empty;
+        if (string.IsNullOrWhiteSpace(name) || string.IsNullOrWhiteSpace(code))
+        {
+            throw new BusinessException(ErrorCodes.BadRequest, "角色名称与编码不能为空");
+        }
+
+        var exists = await roleRepository.FindByCodeAsync(code, tenantId, cancellationToken);
+        if (exists is not null)
+        {
+            throw new BusinessException(ErrorCodes.Conflict, "角色编码已存在");
+        }
+
+        // 3. 构建角色实体
         var role = new Role
         {
             TenantId = tenantId,
-            Name = request.Name,
+            Name = name,
-            Code = request.Code,
+            Code = code,
             Description = request.Description
         };
 
-        // 3. 持久化
+        // 4. 持久化
         await roleRepository.AddAsync(role, cancellationToken);
         await roleRepository.SaveChangesAsync(cancellationToken);
 
-        // 4. 返回 DTO
+        // 5. 返回 DTO
         return new RoleDto
         {
             Id = role.Id,