.Net core/EF：无法访问已处置的对象。此错误的常见原因是处理上下文

Question

我正在使用 Net core，并且正面临这个著名的问题，我有这个示例：

var model = await context.MethAppointementsPreventifs
            .FirstOrDefaultAsync(item => item.StartDate >= DateTodelete 
            && item.IdOperation == XpertHelper.IdOperation);
if (model != null)
{
 var OpInfos = await context.MethOperations.AsNoTracking()
               .FirstOrDefaultAsync(item => item.Idoperation == model.IdOperation);
 context.MethAppointementsPreventifs.Remove(model);
 await context.SaveChangesAsync();
}

当我得到我的“模型”和“OpInfos”时，没有设置上下文或抛出异常，但在以下行中：

context.MethAppointementsPreventifs.Remove(model);

它抛出异常，我的方法不返回异步 void：

public static async Task<int> ClearAppPreventif(KBFsteelContext context)
{
    //clear from the day of intervention 
    var DateTodelete = XpertHelper.DateIntervention;
    bool IsStill = true;
    while (IsStill)
    {
        var model = await context.MethAppointementsPreventifs
            .FirstOrDefaultAsync(item => item.StartDate >= DateTodelete && item.IdOperation == XpertHelper.IdOperation);
        if (model != null)
        {
            var OpInfos = await context.MethOperations.AsNoTracking().FirstOrDefaultAsync(item => item.Idoperation == model.IdOperation);
            context.MethAppointementsPreventifs.Remove(model);
            await context.SaveChangesAsync();
            if (OpInfos.Unité == 1)
            {
                var newDayDate = DateTodelete.AddDays(OpInfos.Fréquence);
                DateTodelete = newDayDate;
            }//jours
            if (OpInfos.Unité == 2)
            {
                var newDayDate = DateTodelete.AddMonths(OpInfos.Fréquence);
                DateTodelete = newDayDate;
            }//Mois
            if (OpInfos.Unité == 3)
            {
                var newDayDate = DateTodelete.AddYears(OpInfos.Fréquence);
                DateTodelete = newDayDate;
            }//Annees
        }
        else
        {
            IsStill = false;
        }
    }
    return 1;
}

我用 await 调用它...那我该怎么办？

Answer 1

也许您的 OpInfos 正在被破坏。特别是如果您有级联删除行为。为什么你不把你的代码改成这样：

....your code

if (model != null)
{
var operationId=model.IdOperation:
 context.MethAppointementsPreventifs.Remove(model);
var result = await context.SaveChangesAsync();
if (result==0) return 0; //error

var OpInfos = await context.MethOperations.AsNoTracking().FirstOrDefaultAsync(item => item.Idoperation ==operatonId);
if(OpInfos ==null) return 0; //error

 if (OpInfos.Unité == 1)
....continue your code