如何从LINQ实现SQL CASE语句 [英] How can I achieve SQL CASE statement from LINQ

问题描述

我是LINQ的新手，我想知道是否可以从LINQ实现以下SQL查询吗?

I am new to LINQ and I would like to know if I can achieve the below SQL query from LINQ?

我正在使用Entity Framework Core.

I am using Entity Framework Core.

SELECT 0 [All], [Range] =
    CASE  
        WHEN Value BETWEEN 0 AND 25 THEN 'Low' 
        WHEN Value BETWEEN 25 AND 75 THEN 'Medium' 
        WHEN Value BETWEEN 75 AND 90 THEN 'High' 
        WHEN Value BETWEEN 90 AND 100 THEN 'Very High' 
    END 
FROM Result.Calculation C 
    INNER JOIN Data.SampleSet S ON C.SampleSetID = S.ID  
WHERE  S.SampleDrawn >= DATEADD(MONTH,-3,GETDATE()) AND S.Department = 'LOCATION A'

当前，我正在按以下方式使用FromSql来调用存储过程.我想知道是否可以在不使用存储过程的情况下做到这一点?

Currently, I am using FromSql as below to call a stored procedure. I would like to know whether I can do the same without using stored procedures?

var结果= context.MyData.FromSql("data.GetMyData @pType = {0}，@ pLocation = {1}，@ pNoOfDays = {2}，@ pStartDate = {3}，@ pEndDate = {4} ，类型，位置，noOfDays，startDate，endDate).ToList();

var result = context.MyData.FromSql("data.GetMyData @pType = {0}, @pLocation = {1}, @pNoOfDays = {2}, @pStartDate = {3}, @pEndDate = {4}", type, location, noOfDays, startDate, endDate).ToList();

谢谢.

推荐答案

如果适合您可以使用它. 我只解释LINQ查询部分. 您可以将其与EF一起使用.我为这些创建了虚拟数据. 对于EF，请改用IQueryable.

You can use this if it suits you. I would just explain the LINQ query part. You can use this with EF. I created dummy data for these. For EF, use IQueryable instead.

// from a row in first table
// join a row in second table
// on a.Criteria equal to b.Criteria
// where additional conditions
// select the records into these two fields called All and Range
// Convert the result set to list.
var query = (from a in lstCalc
join b in lstSampleSet
on a.SampleSetID equals b.ID where b.SampleDrawn >= DateTime.Now.AddMonths(-8)
&& b.Department == "Location A"
select new { All = 0, Range = Utilities.RangeProvider(a.Value) }).ToList();

LINQ查询分组结果..确保您正在使用IQueryable.

EDIT : LINQ Query for grouped result.. Make sure you are using IQueryable.

 var query = (from a in lstCalc
  join b in lstSampleSet
  on a.SampleSetID equals b.ID where b.SampleDrawn >= DateTime.Now.AddMonths(-8) 
   && b.Department == "Location A"
    group a by Utilities.RangeProvider(a.Value) into groupedData
     select new Result { All = groupedData.Sum(y => y.Value), Range = 
   groupedData.Key }).ToList();

这是相同的代码.

 public class Program
    {
        public static void Main(string[] args) {
            List<Calculation> lstCalc = new List<Calculation>();
            lstCalc.Add(new Calculation() {SampleSetID=1, Value=10 });
            lstCalc.Add(new Calculation() { SampleSetID = 1, Value = 10 });
            lstCalc.Add(new Calculation() { SampleSetID = 2, Value = 20 });
            lstCalc.Add(new Calculation() { SampleSetID = 3, Value = 30 });
            lstCalc.Add(new Calculation() { SampleSetID = 4, Value = 40 });
            lstCalc.Add(new Calculation() { SampleSetID = 5, Value = 50 });
            lstCalc.Add(new Calculation() { SampleSetID = 6, Value = 60 });
            lstCalc.Add(new Calculation() { SampleSetID = 7, Value = 70 });
            lstCalc.Add(new Calculation() { SampleSetID = 8, Value = 80 });
            lstCalc.Add(new Calculation() { SampleSetID = 9, Value = 90 });

            List<SampleSet> lstSampleSet = new List<SampleSet>();
            lstSampleSet.Add(new SampleSet() {Department = "Location A", ID=1, SampleDrawn=DateTime.Now.AddMonths(-5)});
            lstSampleSet.Add(new SampleSet() { Department = "Location A", ID = 2, SampleDrawn = DateTime.Now.AddMonths(-4) });
            lstSampleSet.Add(new SampleSet() { Department = "Location A", ID = 3, SampleDrawn = DateTime.Now.AddMonths(-3) });
            lstSampleSet.Add(new SampleSet() { Department = "Location A", ID = 4, SampleDrawn = DateTime.Now.AddMonths(-2) });
            lstSampleSet.Add(new SampleSet() { Department = "Location A", ID = 5, SampleDrawn = DateTime.Now.AddMonths(-2) });
            lstSampleSet.Add(new SampleSet() { Department = "Location A", ID = 6, SampleDrawn = DateTime.Now.AddMonths(-2) });
            lstSampleSet.Add(new SampleSet() { Department = "Location A", ID = 7, SampleDrawn = DateTime.Now.AddMonths(-1) });

            var query = (from a in lstCalc
                        join b in lstSampleSet
                        on a.SampleSetID equals b.ID where b.SampleDrawn >= DateTime.Now.AddMonths(-8)
                         && b.Department == "Location A"
                        select new { All = 0, Range = Utilities.RangeProvider(a.Value) }).ToList();

            Console.WriteLine(query.Count);
            Console.ReadLine();

        }


    }

        public class Utilities
        {
            public static string RangeProvider(int value)
            {
                if (value > 0 && value <= 25)
                { return "Low"; }
                if (value > 25 && value <= 75)
                { return "Medium"; }
                if (value > 75 && value <= 90)
                { return "High"; }
                else
                { return "Very High"; }
            }

        }

    public class Result {
      public int All { get; set; }
      public string Range { get; set; }
   }

    public class Calculation
    {
        public int SampleSetID { get; set; }
        public int Value { get; set; }

    }

    public class SampleSet
    {
        public int ID { get; set; }
        public DateTime SampleDrawn { get; set; }

        public string Department { get; set; }

    }

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