使用Linq更新列表

Question

我正在创建两个对象列表。 一个“新”列表，一个“旧列表”。

我想从新列表上的对象中获取一个属性的值，并在匹配对象的旧列表上将属性设置为新值。

//Original Solution
        foreach (RyderQuestion quest in myList)
        {
            //compare it to every question in ryder questions
            foreach (RyderQuestion oldQuestion in _ryderQuestions)
            {
                //if the question ids match, they are the same question, and should have the right selected option
                //selecting the option sets the checkbox of the MultipleChoideQuestionControl
                if (oldQuestion.QuestionID == quest.QuestionID)
                {
                    oldQuestion.SelectedOption = quest.SelectedOption;
                }
            }
        }

我正在尝试将其转换为LINQ，以使用联接使其更有效，但是如何直接更新该值？

        var x = from quest in myList
                join oldquest in _ryderQuestions
                on new { quest.QuestionID, quest.ShowOn, quest.QuestionOrder }
            equals new { oldquest.QuestionID, oldquest.ShowOn, oldquest.QuestionOrder }
                select oldquest.SelectedOption = quest.SelectedOption;

该查询将值返回到x列表，但是我实际上想更新旧列表中的对象。

Answer 1

Linq用于查询 ，而不用于更新 。 您可以将两个列表连接起来以排队更新对象，但是仍然需要循环进行更改：

var query = from quest in myList
            join oldquest in _ryderQuestions
            on new { quest.QuestionID, quest.ShowOn, quest.QuestionOrder }
        equals new { oldquest.QuestionID, oldquest.ShowOn, oldquest.QuestionOrder }
            select new {oldquest, quest};

foreach(var item in query}
    item.oldquest.SelectedOption = item.quest.SelectedOption

Answer 2

例如：

var x = from quest in myList
            join oldquest in _ryderQuestions
            on new { quest.QuestionID, quest.ShowOn, quest.QuestionOrder }
        equals new { oldquest.QuestionID, oldquest.ShowOn, oldquest.QuestionOrder }

            select new {quest , oldquest};

foreach(var item in x)
{
    item.quest.SelectedOption = item.oldquest.SelectedOption;
}

你是这个意思？