Question

我正在试图找出处理简单问题的最佳方法：我有一个简单的LINQ连接到两个表。我知道如何返回一个表的类型，因为它与生成的dbml类相同。但是，如果我想从两个表中返回数据怎么办？是不是有办法返回两者并使用它们的关系？我是否真的必须创建另一个返回类型以从两个表返回数据？仅供参考 - 我不想用另一个表对象返回输出参数;我对返回匿名类型也不是很感兴趣。什么是最佳做法推荐？

    public IQueryable<Consumer_Question> GetQuestions(int subCategoryId)
    {
        //create DataContext
        MototoolsDataContext mototoolsDataContext = new MototoolsDataContext();
        mototoolsDataContext.Log = Console.Out;

        var subcategoriestag = (from subCatTag in mototoolsDataContext.Consumer_SubCategoriesTags
                                join tagQuestion in mototoolsDataContext.Consumer_TagQuestions on subCatTag.TagID equals tagQuestion.TagID
                                join question in mototoolsDataContext.Consumer_Questions on tagQuestion.QuestionsID equals question.ID
                                where subCatTag.SubCategoriesID == subCategoryId
                                orderby subCatTag.ID descending
                                select question);
                                //select new { question, tagQuestion });

        return subcategoriestag;
    }

感谢您的帮助，

Answer 1

如果您已经在LINQ-to-SQL设计器中定义了关系，那么您的上述查询根本不需要连接语法，只需根据需要“走树”，例如：

var subCategoriesTag = (
    from subCatTag in motoToolsDataContext
    from tagQuestion in subCatTag.TagQuestions
    from question in tagQuestion
    where subCatTag.SubCategoriesID == subcategoryId
    orderby subCatTag.ID descending
    select question
);

请注意，第2个和第3个'from'语句使用的是上一个对象，因为LINQ-to-SQL应该已经知道了这个关系。

如果不了解您的关系，就很难给出更准确的答案。我不得不对相关属性做出一些假设。

Answer 2

听起来像你正在寻找的是DataLoadOptions.LoadWith＆lt;＆gt;。这样您就可以返回Question对象，并通过定义的关联同时填充相关对象。像这样：

public IQueryable<Consumer_Question> GetQuestions(int subCategoryId)
{
    //create DataContext
    using (MototoolsDataContext mototoolsDataContext = new MototoolsDataContext())
    {
        mototoolsDataContext.Log = Console.Out;
        DataLoadOptions options = new DataLoadOptions();
        options.LoadWith<Consumer_Questions>(q => q.Consumer_TagQuestions);
        options.LoadWith<Consumer_TagQuestions>(tag => tag.Consumer_SubCategoriesTags);
        mototoolsDataContext.LoadOptions = options;

        var questions = (from subCatTag in mototoolsDataContext.Consumer_SubCategoriesTags
                                join tagQuestion in mototoolsDataContext.Consumer_TagQuestions on subCatTag.TagID equals tagQuestion.TagID
                                join question in mototoolsDataContext.Consumer_Questions on tagQuestion.QuestionsID equals question.ID
                                where subCatTag.SubCategoriesID == subCategoryId
                                orderby subCatTag.ID descending
                                select question);
                                //select new { question, tagQuestion });

        return questions;
    }
}

Linq to SQL：不是由dbml生成的多表连接返回类型

2 个答案: