Dynamic LINQ Sub Query

c# dynamic-linq linq

Question

I have LINQ query that I want to generate dynamically:

var groupData =
    from l in data
    group l by l.Field1 into field1Group
    select new MenuItem()
    {
        Key = field1Group.Key,
        Count = field1Group.Count(),
        Items = (from k in field1Group
                 group k by k.Field2 into field2Group
                 select new MenuItem()
                 {
                     Key = field2Group.Key,
                     Count = field2Group.Count()
                 }).ToList()
    };

The ultimate goal is to be able to dynamically group the data by any combination of fields with no limit on the nested queries.

I can get as far as the first level but I'm struggling with the nested sub queries:

string field1 = "Field1";
string field2 = "Field2";

var groupDataD =
    data.
    GroupBy(field1, "it").
    Select("new ( it.Key, it.Count() as Count )");

Is this possible with chained dynamic LINQ? Or is there a better way to achieve this?

1
1
1/28/2019 11:45:15 AM

Popular Answer

The following should work (though personally I would rather avoid using such code):

  1. Follow this answer to add the following in ParseAggregate, :

    Expression ParseAggregate(Expression instance, Type elementType, string methodName, int errorPos)
    {
       // Change starts here
       var originalIt = it;
       var originalOuterIt = outerIt;
       // Change ends here
    
       outerIt = it;
       ParameterExpression innerIt = Expression.Parameter(elementType, elementType.Name);
       it = innerIt;
       Expression[] args = ParseArgumentList();
    
       // Change starts here
       it = originalIt;
       outerIt = originalOuterIt;
       // Change ends here
    
       ...
    }
    
  2. Add Select, GroupBy, ToList into IEnumerableSignatures, and respective conditions in ParseAggregate, as explained in this answer:

    interface IEnumerableSignatures
    {
      ...
      void GroupBy(object selector);
      void Select(object selector);
      void ToList();
      ...
    }
    
    Expression ParseAggregate(Expression instance, Type elementType, string methodName, int errorPos)
    {
       ...
       if (signature.Name == "Min" || 
           signature.Name == "Max" || 
           signature.Name == "GroupBy" || 
           signature.Name == "Select")
       ...
    }
    
  3. Finally, Your query would be:

    string field1 = "Field1";
    string field2 = "Field2";
    
    var result =
        data
        .GroupBy(field1, "it")
        .Select($@"new ( 
           it.Key,
           it.Count() as Count,
           it.GroupBy({field2})
             .Select(new (it.Key, it.Count() as Count))
             .ToList() as Items
        )");
    

    Note that "it" holds a different instance when used in the parent query vs. the subquery. I tried to take advantage of "outerIt" to overcome this conflation, but unfortunately without success (but maybe you'd succeed? maybe 1, 2 would help)

  4. A simple example for future reference:

    public class Person
    {
        public string State { get; set; }
        public int Age { get; set; }
    }
    public static Main()
    {
        var persons = new List<Person>
        {
           new Person { State = "CA", Age = 20 },
           new Person { State = "CA", Age = 20 },
           new Person { State = "CA", Age = 30 },
           new Person { State = "WA", Age = 60 },
           new Person { State = "WA", Age = 70 },
        };
        var result = persons
            .GroupBy("State", "it")
            .Select(@"new ( 
               it.Key,
               it.Count() as Count,
               it.GroupBy(Age)
                 .Select(new (it.Key, it.Count() as Count))
                 .ToList() as Items
            )");
         foreach (dynamic group in result)
         {
             Console.WriteLine($"Group.Key: {group.Key}");
             foreach (dynamic subGroup in group.Items)
             {
                 Console.WriteLine($"SubGroup.Key: {subGroup.Key}");
                 Console.WriteLine($"SubGroup.Count: {subGroup.Count}");
             }
         }
    }
    
0
8/20/2019 3:37:54 PM


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