Linq更新单行查询？

Question

我试图在单行的列上执行简单的UPDATE。我收到Sequence contains no elements例外。

private void InsertUpdateFileLocation(string targetFileLocationAndFullName, 
    tbFileAttachment linkGuid)
{
    ISESEntities context = new ISESEntities();

    var query = (from f in context.tbFileAttachments
                 where f.CCCPGUID == linkGuid.CCCPGUID
                 select f).First();

    query.FileLocation = targetFileLocationAndFullName;

    context.SaveChanges();
}

Answer 1

在这种情况下，您没有与您要搜索的值匹配的记录。您可以使用FirstOrDefault然后测试null：

来捕获此信息

var query = (from f in context.tbFileAttachments
             where f.CCCPGUID == linkGuid.CCCPGUID
             select f).FirstOrDefault();

if(query==null) 
{
    //no match found!
}