怎么判断数据是否存在

[江边老乌龟]

一条不存在的数据通过service层的方法可以实例化出来

Member member = memberService.findBySn(sn);

再通过这个实例化出来的对象去拿数据

System.out.println(member.getDelStorageInventorys().size());

这样会报空指针异常，因为我传进来的这个sn是新的，数据库里找不到对应的member,但为什么能实例化呢？
我现在想通过这个sn去判断member是否存在，该怎么做呀？

//如果member存在则执行以下操作
if (member.getDelStorageInventorys().size() == 0) {
			
}

我现在这样判断根本不起作用，，，执行不到里面的化码。新人。求高手指点下呀，

[身胖不怕影子歪]

if(member == null){ //实例化 }

[学到了吗]

先判断对象，要在对象调用方法之前判断

[风一样的执着]

先判读member对象

[blueskyliulan]

3楼说的，先判读member对象

[江边老乌龟]

Member member = this.memberService.findBySn(sn);
		if (member == null) {
			delStorageInventory.setMember(this.memberService.findBySn(sn));
			delStorageInventory.setOperator(this.adminService.getCurrent());
			delStorageInventory.setDelStorage(this.delStorageService.find(delStorageId));
			delStorageInventory.setSn(this.snService.generate(Sn.Type.delStorageInventory));
			/** 数据验证 */
			if(!isValid(delStorageInventory, new Class[0])) {
				return ERROR_VIEW;
			}
			this.delStorageInventoryService.save(delStorageInventory);
		}

Column 'member' cannot be null

“先判读member对象”要怎么写啊，上面我的代码报的错。

[jarydon]

Member member = this.memberService.findBySn(sn); if (member != null&&member.getDelStorageInventorys()!=null&&member.getDelStorageInventorys().size()>0) { delStorageInventory.setMember(this.memberService.findBySn(sn)); delStorageInventory.setOperator(this.adminService.getCurrent()); delStorageInventory.setDelStorage(this.delStorageService.find(delStorageId)); delStorageInventory.setSn(this.snService.generate(Sn.Type.delStorageInventory)); /** 数据验证 */ if(!isValid(delStorageInventory, new Class[0])) { return ERROR_VIEW; } this.delStorageInventoryService.save(delStorageInventory); }

[程序猿_死神]

引用 6 楼 jarydon 的回复:

Member member = this.memberService.findBySn(sn); if (member != null&&member.getDelStorageInventorys()!=null&&member.getDelStorageInventorys().size()>0) { delStorageInventory.setMember(this.memberService.findBySn(sn)); delStorageInventory.setOperator(this.adminService.getCurrent()); delStorageInventory.setDelStorage(this.delStorageService.find(delStorageId)); delStorageInventory.setSn(this.snService.generate(Sn.Type.delStorageInventory)); /** 数据验证 */ if(!isValid(delStorageInventory, new Class[0])) { return ERROR_VIEW; } this.delStorageInventoryService.save(delStorageInventory); }