EF The instance of entity type 'XX' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked

使用EF的时候，获得了一个Alist,先对Alist的子项做了修改，然后把Alist丢到新方法里面，新方法用Blist做了循环接受然后做update（），此时系统报错

System.InvalidOperationException: The instance of entity type 'PaperDocument' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.

原代码

foreach (var t in papers)
{
t.Status = status;
t.DelayReason = $"{UserAccount}操作撤销";
t.ClosingDeadline = DateTime.Now.AddDays(2).Date;
}

UpdatePaperDocumentStatus(papers);

public int UpdatePaperDocumentStatus(List paperDocuments)
{

List papers = new List();
List paperDistributions = new List();
foreach (PaperDocument item in paperDocuments)
{
PaperDocument dbPaperDoc = this.dataContext.PaperDocuments.AsNoTracking()
.FirstOrDefault(t => t.Id == item.Id);

if (dbPaperDoc == null)
continue;
dbPaperDoc.Status = item.Status;//改变状态
papers.Add(dbPaperDoc);
}

this.dataContext.PaperDistributions.UpdateRange(paperDistributions);
this.dataContext.PaperDocuments.UpdateRange(papers);
return this.dataContext.SaveChanges();

}

修改后代码

foreach (var t in papers)
{
t.Status = status;
t.DelayReason = $"{UserAccount}操作撤销";
t.ClosingDeadline = DateTime.Now.AddDays(2).Date;

this._dataContext.SaveChanges();
this._dataContext.Entry(t).State = EntityState.Detached;
}

其余代码不变