避免重复插入数据库

Question

我有以下代码插入一个具有随机生成值“hawb”的实体作为列之一。我的想法是，因为hawb是表中的唯一列，所以 try-catch 块将在插入重复值时捕获异常。工作流程工作正常，直到我开始测试它并出现一些奇怪的错误。

[Code]

hawb = "0402135505536";

while (!uniqueHawb)  //insert new hawb

{

    //hawb = $"{DateTime.Now:MMddHHmmss}{RandomHelper.GetRandomNumber(0, 999):000}";

    var entity = new HawbAsset { HAWB = hawb, HawbStatus = "Allocated", AllocatedDateTime = DateTime.Now, AllocationReference = reference };

    try

    {

        _repository.Insert(entity);

        uniqueHawb = true;

    }

    catch (Exception e)

    {

        ;

    }

    hawb = $"{DateTime.Now:MMddHHmmss}{RandomHelper.GetRandomNumber(0, 999):000}";

}

[Model]

    public class HawbAsset : BaseEntity

    {

        [Required(AllowEmptyStrings = false)]

        [Index(IsUnique = true)]

        [StringLength(15)]

        public string HAWB { get; set; }

        [Required(AllowEmptyStrings = false)]

        public string HawbStatus { get; set; }

        public DateTime? AllocatedDateTime { get; set; }

        [Required(AllowEmptyStrings = false)]

        public string AllocationReference { get; set; }

        public DateTime? ConfirmedUsageDateTime { get; set; }

        public DateTime? RecycledDateTime { get; set; }

        public string Owner { get; set; }

    }

我硬编码了一个重复值 0402135505536，因此它会在第一时间捕获“重复键异常”，这是预期的。然而，当 hawb 是随机生成的，并且我已经确定值不同时，它仍然会捕获相同的“Duplicate Key Exception”。谁能告诉我发生了什么以及如何实现我的目标？谢谢！

Answer 1

您看到的问题是因为您尝试插入一个具有重复 ID 的实体但失败了。重试时，您正在创建第二个实体并尝试插入它。第一个实体仍与上下文相关联，并且仍将尝试保存。在保存新替换或更新现有实体之前，您需要将其与上下文分离。（以下）hawb = "0402135505536";var entity = new HawbAsset { HAWB = hawb, HawbStatus = "Allocated", AllocatedDateTime = DateTime.Now, AllocationReference = reference };while (!uniqueHawb)&nbsp; //insert new hawb{&nbsp; &nbsp; //hawb = $"{DateTime.Now:MMddHHmmss}{RandomHelper.GetRandomNumber(0, 999):000}";&nbsp; &nbsp; try&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; _repository.Insert(entity);&nbsp; &nbsp; &nbsp; &nbsp; uniqueHawb = true;&nbsp; &nbsp; }&nbsp; &nbsp; catch (Exception e)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; ;&nbsp; &nbsp; }&nbsp; &nbsp; entity.HAWB = $"{DateTime.Now:MMddHHmmss}{RandomHelper.GetRandomNumber(0, 999):000}";}要分离您需要使用的实体，context.Entity(entity).State = EntityState.Detached; 它需要通过您的存储库边界进行操作。理想情况下，最好在尝试插入之前检查 HAWB 的唯一性，但仍然处理那些非常非常罕见的情况，即在检查和保存之间保存条目：int retryCount = 0while (retryCount < 5){&nbsp; try&nbsp; {&nbsp; &nbsp; bool isUnique = false;&nbsp; &nbsp; string hawb = null;&nbsp; &nbsp; while(!isUnique)&nbsp; &nbsp; {&nbsp;&nbsp; &nbsp; &nbsp; hawb = generateHawb();&nbsp; &nbsp; &nbsp; isUnique = context.HawbAssets.Any(x => x.HAWB == hawb);&nbsp; &nbsp; }&nbsp; &nbsp; entity.HAWB = hawb; // this hawb should be unique, so set and insert.&nbsp; &nbsp; _repository.Insert(entity);&nbsp; }&nbsp; catch(UpdateException)&nbsp; {&nbsp; // log that this has happened, check inner exception for duplicate key and retry, though limit retry attempts if there are deeper issues that might lock up the system in a retry loop.&nbsp; &nbsp; retryCount++;&nbsp; }}

Answer 2

它的 1 行额外代码用于检查实体是否存在。先做这件事，不要依赖错误处理来完成工作：if ( _repository.HAWBAssets.FirstOrDefault(i => i.HAWB == hawb)== null)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp;_repository.Insert(entity);&nbsp; &nbsp; &nbsp; &nbsp; uniqueHawb = true;&nbsp; &nbsp; }

Answer 3

也许您可以使用纳秒来使记录之间的距离变大，以减少重复的可能性entity.HAWB = $"{DateTime.Now.Ticks}";// 636898603227146583DateTime.Ticks分辨率为 100 纳秒