潜在列不固定时的 LINQ 部分交叉表查询

Question

我需要生成用于导出的“扁平化”数据版本，客户希望相关的表行显示为列。我们正在使用实体框架 4 和 .NET 4.0

客户可以为其活动创建自定义问题。可能有零到无限的问题。参加活动的用户可能不回答、部分或全部这些问题。

我需要制作的是这样的：

User 1    User 1 info field A   User 1 info field B    User 1 Answer to question A    User 1 Answer to Question B
User 2    User 2 info field A   User 2 info field B    User 2 Answer to question A    User 2 Answer to Question B

创建结果集的用户信息部分不是问题，但我对如何获取相关问题和答案感到困惑，即：

from urf in tblUserRegistrationFields.Include("tblRegistrationFields")
where urf.UserID == eachUserID && urf.tblRegistrationField.EventID == thisEventID
select new
{
    FieldLabel = urf.tblRegistrationField.FieldLabel, //this is the question name
    value = urf.value //this is the user's answer
}

并将这些作为单独的列添加到我的用户选择语句中，即：

var users = from u in context.tblUsers
            <snip>
            select new
            {
                UserID = u.UserID,
                <snip>,
                CustomQuestionA = AnswerA,
                CustomQuestionB = AnswerB,
                ... etc.
            };

最终我需要创建一个网格，然后我可以将其导出为所需的格式，并且我对非 LINQ 解决方案持开放态度（尽管购买 3rd 方控件不是一种选择。）我怀疑有一种方法可以利用 LINQ 的分组功能，但我无法将其应用于此场景。

Answer 1

我找到了一种在 SQL 中进行动态数据透视的方法，但无法让它与 两个 相关的表一起工作，只有一个。动态 SQL 枢轴点在这里： http://www.simple-talk.com/blogs/2007/09/14/pivots-with-dynamic-columns-in-sql-server-2005/

最终，我退回并手动创建了一个数据集。这当然不是一个优化的解决方案，但它为客户提供了他们想要的东西。对于大量数据，我不推荐这种方法。

我创建了数据集和数据表的固定列，然后遍历问题列表：

//get the list of questions
var context = new EventRegistrationEntities();
var customQuestions = from rf in context.tblRegistrationFields
                      where rf.EventID == vEventID
                      select new
                      {
                          RegistrationFieldID = rf.RegistrationFieldID,
                          FieldLabel = rf.FieldLabel
                      };

//add a question column for each question
List<string> extracolumns = new List<string>();

foreach (var q in customQuestions)
{
    dt.Columns.Add(q.FieldLabel, typeof(string));

    //store the question names for later user
    extracolumns.Add(q.RegistrationFieldID.ToString() + "-" + q.FieldLabel.ToString());
}

接下来，我循环遍历用户列表并插入固定数据，然后在该循​​环中（呃）添加用户的答案：

foreach (var c in extracolumns) //these are the custom *questions*
{
    int regID = Convert.ToInt32(c.Substring(0, c.IndexOf("-")));
    string question = c.Substring(c.IndexOf("-") + 1); //we need to pass the question text (aka column header) in because if the user hasn't answered the question we have no access to it from here

    //get the question answer
    var userAnswer = (from urf in context.tblUserRegistrationFields.Include("tblRegistrationFields")
                      where urf.UserID == u.UserID && urf.RegistrationFieldID == regID
                      select new
                      {
                          Question = urf.tblRegistrationField.FieldLabel,
                          Answer = urf.value
                      }).FirstOrDefault();

     //add the answer to the data row
     if (userAnswer != null)
     {
         dr[question] = userAnswer.Answer.ToString();
     }
     else
     {
         dr[question] = ""; //if the user has not answered the question, insert a blank
     }
 }