集成自定义的方法到LINQ到实体查询 [英] Integrating custom method into LINQ to Entities query

问题描述

我有，其对一组数据的一些计算一个自定义的方法：

I have a custom method that performs some calculation on a set of data:

 private int GetPercentages(int OriginalValue, int TotalValue)
        {
            var newValue = (int)Math.Round(((decimal)OriginalValue / (decimal)TotalValue) * 100);

            return newValue;
         }

我需要能够到LINQ内运行这个方法来Entities查询：

I need to be able to run this method inside of a LINQ to Entities query:

var data = from SurveyResponseModel in db.SurveyResponseModels
                       group SurveyResponseModel by SurveyResponseModel.MemberId into resultCount
                       select new ResultsViewModel()
                       {
                           MemberId = resultCount.Key,
                           PatientFollowUpResult = db.SurveyResponseModels.Count(r => r.PatientFollowUp),
                           PatientFollowUpResultPct = GetPercentages(db.SurveyResponseModels.Count(r => r.PatientFollowUp),totalResponsesResult),
                           ChangeCodingPracticeResult = db.SurveyResponseModels.Count(r => r.ChangeCodingPractice),
  };

我需要在查询里面的约20条线运行这​​个所以就坚持它内联似乎并不像一个很好的选择。据我所知，它需要被转换成SQL语法，但有别的像这样，我还能做什么？

I need to run this on about 20 more lines inside of the query so just sticking it inline doesn't seem like a great option. I understand that it needs to be converted into SQL syntax, but is there anything else like this that I can do?

推荐答案

您需要做的lambda前pression，计算这样的百分比：

You need to make a lambda expression that calculates the percentage like this:

Expression<Func<int, int, int>> calcPercentage =
    (OriginalValue, TotalValue) => (int)Math.Round(((decimal)OriginalValue / (decimal)TotalValue) * 100);

和使用这样的：

var data = from SurveyResponseModel in db.SurveyResponseModels.ToExpandable()
           group SurveyResponseModel by SurveyResponseModel.MemberId into resultCount
           select new ResultsViewModel()
           {
               MemberId = resultCount.Key,
               PatientFollowUpResult = db.SurveyResponseModels.Count(r => r.PatientFollowUp),
               PatientFollowUpResultPct = calcPercentage.Invoke(db.SurveyResponseModels.Count(r => r.PatientFollowUp), totalResponsesResult),
               ChangeCodingPracticeResult = db.SurveyResponseModels.Count(r => r.ChangeCodingPractice),
           };

有关LINQ调用函数更多信息查询这里。

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