如何从Linq语法转换为动态语法

本文关键字：语法 转换 动态 Linq | 更新日期: 2023-09-27 18:02:08

我使用的是System.Linq.Dynamic (http://msdn.microsoft.com/en-us/vstudio//bb894665.aspx)类。它用于定义动态Linq查询。我需要我的查询是动态的，这样它们就可以在运行时定义。

我将用一个例子来解释:有一个包含Transaction对象列表的Transactions对象。

public class Transactions : List<Transaction>
{
    public Transactions() { }
    public Transactions(List<Transaction> trans) : base(trans) { }
}
public class Transaction
{
    public string Type;
    public int Value;
}

假设我声明了Transactions对象并填充了一些数据:

Transactions trans = new Transactions
{
    new Transaction {
        Type = "A",
        Value = 20,
    },
    new Transaction {
        Type = "B",
        Value = 34,
    },
    ... and so on
};

我可以像这样运行Linq查询从trans中提取一些数据:

var mySum = from tran in trans
            group tran by tran.Type into tranGroup
            select new
            {
                Type = tranGroup.Key,
                Total = tranGroup.Sum(s => s.Value)
            };

可以(不那么容易)转录为以下动态查询

var mySum = trans
    .AsQueryable()
    .GroupBy("new(Type)", "new(Value)")
    .Select("new(Key.Type as Type, Sum(Value) as Total)");

它所做的是给出一个对象，其中Type作为分组类型，Total作为特定组的sum Value。例如，它可能看起来像这样:

mySum = [{Type:"A", Total: 120},{Type:"B", Total: 200},{Type:"C", Total: 60}]

我了解动态查询的基本原理，但似乎没有任何复杂动态查询的清晰示例，包括对发生的事情的解释。

这是我不能解决的部分。给定以下Linq查询:

var myQuery = from tran in trans
              group tran by tran.Type into tranGroup
              select new
              {
                  Type = (tranGroup.Key == "A" ? "Alfa" : (tranGroup.Key == "B" ? "Bravo" : (tranGroup.Key == "C" ? "Charlie" : (tranGroup.Key == "D" ? "Delta" : "")))),
                  Data = (from tranValue in tranGroup
                          select tranValue.Value).ToList()
              };

最终会得到如下的结果:

myQuery = [{Type:"Alfa", Data: [50,60,10]},{Type:"Bravo", Data: [60,70,40,30]},{Type:"Charlie", Data: [10,30,5,15]}]

就是这样动态地写，但是没有嵌套:

var myQuery = trans
    .AsQueryable()
    .GroupBy("new(Type)", "new(Value)")
    .Select(@"new((Key.Type == ""A"" ? ""Alfa"" : (Key.Type == ""B"" ? ""Bravo"" : (Key.Type == ""C"" ? ""Charlie"" : (Key.Type == ""D"" ? ""Delta"" : ""Other"")))) as Type, """" AS Data)");

我如何写上面的动态查询包括嵌套数组的值?

谁能给我指出一些好的例子的方向，或者给我一些例子，包括如何分组和求和?

如何从Linq语法转换为动态语法

我自己想出来的

问题是我在执行"new(Value) " "Value"在上面我应该只做"Value"。我看到了一个使用它作为参数的示例查询。基本上它表示当前项目。

这是一个Linq查询 

var myQuery = from tran in trans
              group tran by tran.Type into tranGroup
              select new
              {
                  Type = (tranGroup.Key == "A" ? "Alfa" : (tranGroup.Key == "B" ? "Bravo" : (tranGroup.Key == "C" ? "Charlie" : (tranGroup.Key == "D" ? "Delta" : "")))),
                  Data = (from tranValue in tranGroup
                          select tranValue.Value).ToList()
              };

，可以转录成动态查询

var myQuery = trans
    .AsQueryable()
    .GroupBy("new(Type)", "Value")
    .Select(@"new((Key.Type == ""A"" ? ""Alfa"" : (Key.Type == ""B"" ? ""Bravo"" : (Key.Type == ""C"" ? ""Charlie"" : (Key.Type == ""D"" ? ""Delta"" : ""Other"")))) as Type, it AS Data)");

返回的结果类似于

myQuery = [{Type:"Alfa", Data: [50,60,10]},{Type:"Bravo", Data: [60,70,40,30]},{Type:"Charlie", Data: [10,30,5,15]}]
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