c# - 在 LINQ 中加入和分组

Question

这些是我的输入表:

Persons Table:
================
ID  Code
------------------------
1   Person1     # Person1: John Smith, 25, 50Kg
2   Person2     # Person2: William Brown, 30, 80Kg
3   Person3     # Person3: James Miller, 32, 73Kg

StringProperties Table:
=========================
ID  PersonID    Name        Value
----------------------------------------------
1   1           FirstName   John        # Person1: John Smith, 25, 50Kg
2   1           LastName    Smith       # Person1: John Smith, 25, 50Kg
3   2           FirstName   William     # Person2: William Brown, 30, 80Kg
4   2           LastName    Brown       # Person2: William Brown, 30, 80Kg
5   3           FirstName   James       # Person3: James Miller, 32, 73Kg
6   3           LastName    Miller      # Person3: James Miller, 32, 73Kg

NumericProperties Table:
=========================
ID  PersonID    Name    Value
-----------------------------------------
1   1           Age     25          # Person1: John Smith, 25, 50Kg
2   1           Weight  50          # Person1: John Smith, 25, 50Kg
3   2           Age     30          # Person2: William Brown, 30, 80Kg
4   2           Weight  80          # Person2: William Brown, 30, 80Kg
5   3           Age     32          # Person3: James Miller, 32, 73Kg
6   3           Weight  73          # Person3: James Miller, 32, 73Kg

我想编写一个生成以下结果的 LINQ 查询:

Result:
==========
Code        FirstName   LastName    Age     Weight
-----------------------------------------------------------------
Person1     John        Smith       25      50
Person2     William     Brown       30      80
Person3     James       Miller      32      73

这是我的代码，但它不能正常工作:

var q = from p in db.Persons
        join s in db.StringProperties on p.ID equals s.PersonID
        join n in db.NumericProperties on p.ID equals n.PersonID
        group p by p.Code into g
        select new
        {
            g.Key,
            g
        };

Answer 1

有很多方法可以解决这个问题。这是一对夫妇。

首先，感谢 DavidG 提供类和输入数据。

这是选项 1:

var query =
    from p in persons
    join s in stringProperties on p.ID equals s.PersonID into gss
    join n in numericProperties on p.ID equals n.PersonID into gns
    from fn in gss.Where(x => x.Name == "FirstName")
    from ln in gss.Where(x => x.Name == "LastName")
    from a in gns.Where(x => x.Name == "Age")
    from w in gns.Where(x => x.Name == "Weight")
    select new
    {
        p.Code,
        FirstName = fn.Value,
        LastName = ln.Value,
        Age = a.Value,
        Weight = w.Value,
    };

这是选项 2:

var query =
    from p in persons
    join s in stringProperties on p.ID equals s.PersonID into gss
    join n in numericProperties on p.ID equals n.PersonID into gns
    let sl = gss.ToLookup(x => x.Name, x => x.Value)
    let nl = gns.ToLookup(x => x.Name, x => x.Value)
    from FirstName in sl["FirstName"]
    from LastName in sl["LastName"]
    from Age in nl["Age"]
    from Weight in nl["Weight"]
    select new
    {
        p.Code,
        FirstName,
        LastName,
        Age,
        Weight,
    };

这两个都给我这个结果: