Question

我正在尝试创建一个由表驱动的多项选择问卷。有一个问题在每个问题中都有子选择。

当我迭代listOfQuestions时，执行第一个SQL。我想通过“包含”选择这可以防止在我循环通过当前问题的选择时发生二次查找，但事实并非如此。

为什么？

  var listOfQuestions = (from q in journeyEastContext.Questions.Include("Choices")
                                   orderby q.QuestionId
                                   select new
                                   {
                                       Question = q,
                                       Choices = q.Choices.OrderBy(c => c.Sequence)
                                   });


            foreach (var questionGroup in listOfQuestions)
            {

                Question question = questionGroup.Question;

                Literal paragraph = new Literal
                {
                    Text = "<P/>"
                };
                this.QuestionPanel.Controls.Add(paragraph);

                Label QuestionLabel = new Label
                {
                    Text = question.Text
                };
                this.QuestionPanel.Controls.Add(QuestionLabel);

                //var sortedChoices = from choices in question.Choices
                //                    orderby choices.Sequence
                //                    select choices;

                foreach (Choice choice in question.Choices)
                {
                    Literal carrageReturn = new Literal
                    {
                        Text = "<BR/>"
                    };
                    this.QuestionPanel.Controls.Add(carrageReturn);

                    RadioButton choiceRadioButton = new RadioButton()
                    {
                        ID = String.Format("{0},{1}", question.QuestionId, choice.ChoiceId),
                        Text = choice.Text,
                        GroupName = question.QuestionId.ToString()
                    };

                    this.QuestionPanel.Controls.Add(choiceRadioButton);
                }
            }

Answer 1

这是因为投影是查询的一部分。

                                   select new
                               {
                                   Question = q,
                                   Choices = q.Choices.OrderBy(c => c.Sequence)
                               });

有几种方法可以解决这个问题，最简单的方法是

  var quesitonsList = (from q in journeyEastContext.Questions.Include("Choices")
                               orderby q.QuestionId).ToList();



var listOfQuestions = from q in questionsList
            Select new
                                   {
                                       Question = q,
                                       Choices = q.Choices.OrderBy(c => c.Sequence)
                                   });

这将告诉EF执行第一个查询（急切加载Choices属性），然后让你在没有激发额外查询的情况下运行迭代。

.Include和.Select不要混用，因为在T-SQL中生成的查询类型。基本上，投影使用内部选择语句，并且急切加载的属性使用非规范化和连接来展平记录集。

实体框架延迟加载问题

1 个答案: