c# - 我不能在此处将我的 ADO.NET 实体模型实例包装在 using 语句中吗？

Question

我有一个 ASP.NET MVC WebAPI 项目，我有一个入口点可以通过 ID 进行调查。

public IEnumerable<Models.SurveyQuestionViewModel> GetSurveyById(int id)
{
    using (ITSurveyEntities model = new ITSurveyEntities())
    {
        var questions = model.SurveyQuestions.Where(s => s.SurveyId == id).AsEnumerable();
        if (!questions.Any())
        {
            throw new HttpResponseException(HttpStatusCode.NotFound);
        }

        return (from q in questions
                select new Models.SurveyQuestionViewModel
                {
                    Id = q.Id,
                    Question = q.Question,
                    LongDescription = q.LongDescription,
                });
    }
}

但是，当我向它发出请求时:

$.getJSON(apiUrl + '/' + id)
    .done(function (item) {
        surveyBusy.hide();
        var o = $('#survey-content');
    })
    .fail(function (jqXHR, textStatus, err) {
        var o = $('.error-bar');

        if (err === 'Not Found') {
            o.text('The survey you requested doesn\'t yet have any questions configured.');
        }
        else {
            o.text('An error occurred: ' + err);
        }

        o.fadeIn();
    });

我陷入了 :fail 处理程序。通过开发人员工具检查实际响应后，我发现根本原因如下:

The operation cannot be completed because the DbContext has been disposed.

我是不是用错了这个对象？我认为一切都很好，因为我正在为初始查询调用 AsEnumerable()，从而直接在前面进行数据库往返。当我到达底部的结果时，它没有进行任何数据库调用。我只是将这些值编码到 View 模型。

Answer 1

您正在延迟查询。试试这个:

return (from q in questions
                select new Models.SurveyQuestionViewModel
                {
                    Id = q.Id,
                    Question = q.Question,
                    LongDescription = q.LongDescription,
                }).ToList();