fix 新增时实体类ID赋值问题

Api/Ewide.Core/Entity/DEntityBase.cs

@@ -19,7 +19,7 @@ namespace Ewide.Core
         [DatabaseGenerated(DatabaseGeneratedOption.None)]
         [Comment("Id主键")]
         [Column("Id", TypeName = "varchar(36)")]
-        public virtual string Id { get; set; } = Guid.NewGuid().ToString();
+        public virtual string Id { get; set; }
 
         /// <summary>
         /// 创建时间

Api/Ewide.EntityFramework.Core/DbContexts/DefaultDbContext.cs

@@ -112,7 +112,7 @@ namespace Ewide.EntityFramework.Core
                     var obj = entity.Entity as DEntityBase;
                     if (entity.State == EntityState.Added)
                     {
-                        obj.Id = Guid.NewGuid().ToString();
+                        obj.Id = string.IsNullOrEmpty(obj.Id) ? Guid.NewGuid().ToString() : obj.Id;
                         obj.CreatedTime = DateTime.Now;
                         if (!string.IsNullOrEmpty(userId))
                         {