dynamic linq expression using select in .NET

Question

I want to dynamically add .Select statements, but the compiler will only allow me to build these statements inside the current scope. I am aware of linqkit, which could be a solution, but i dont want to add any external functionallity. How do i avoid this code duplication which i have now:

 if (request.Equals("some text"))
        {
            var filter = commonFilter.GroupBy(x => new
                {
                    x.Timestamp.Year,
                    x.Timestamp.Month,
                })
                .Select(g => new
                {
                    Year = g.Key.Year,
                    Month = g.Key.Month,
                    TotErr = g.Count(),

                    column1 = g.Sum(o => o.Process.Contains("something") ? 1 : 0),
                    column2= g.Sum(o => o.Process.Contains(".something1") ? 1 : 0),
                    column3= g.Sum(o => o.Process.Contains(".something2") ? 1 : 0),
                    column4= g.Sum(o => o.Process.Contains("something3") ? 1 : 0),
                    column5= g.Sum(o => o.Process.Contains(".something4") ? 1 : 0),
                    column6 = g.Sum(o => o.Process.Contains(".something5") ? 1 : 0),
                    column7= g.Sum(o => o.Process.Contains(".something6") ? 1 : 0),
                    column8= g.Sum(o => o.Process.Contains(".something7") ? 1 : 0),
                    column9= g.Sum(o => o.Process.Contains(".something8") ? 1 : 0),

                    NumOrgs = g.Select(l => l.OrganizationId).Distinct().Count(),
                    NumUsers = g.Select(l => l.UserId).Distinct().Count(),

                });

            return filter.AsPa......;//not important right now
        }
        //Same thing again but slightly different
        else if (request.Equals("some other text"))
        {
            var filter = commonFilter.GroupBy(x => new
                {
                    x.Timestamp.Year,
                    x.Timestamp.Month,
                    x.Timestamp.Day
                })
                .Select(g => new
                {
                    Year = g.Key.Year,
                    Month = g.Key.Month,
                    Day= g.Key.Day,
                    TotErr = g.Count(),

                    column1 = g.Sum(o => o.Process.Contains("something") ? 1 : 0),
                    column2= g.Sum(o => o.Process.Contains(".something1") ? 1 : 0),
                    column3= g.Sum(o => o.Process.Contains(".something2") ? 1 : 0),
                    column4= g.Sum(o => o.Process.Contains("something3") ? 1 : 0),
                    column5= g.Sum(o => o.Process.Contains(".something4") ? 1 : 0),
                    column6 = g.Sum(o => o.Process.Contains(".something5") ? 1 : 0),
                    column7= g.Sum(o => o.Process.Contains(".something6") ? 1 : 0),
                    column8= g.Sum(o => o.Process.Contains(".something7") ? 1 : 0),
                    column9= g.Sum(o => o.Process.Contains(".something8") ? 1 : 0),

                    NumOrgs = g.Select(l => l.OrganizationId).Distinct().Count(),
                    NumUsers = g.Select(l => l.UserId).Distinct().Count(),

                });

            return filter.AsPa......;//not important right now
        }

What is you data source for the linq query? If it is 'Linq to objects' you can invoke a variable delegate. — Myrtle
– Myrtle, Commented Jun 18, 2012 at 14:11
Not sure I understand your actual problem. Couldn't you use named types instead of anonymous one ? you could create a class with all the column fields and create two constructors or a static method to build an instance from a filter ? — Kek
– Kek, Commented Jun 18, 2012 at 14:20
yes i could use named types, however i failed to try and define it. How should I declare it? — Zeezer
– Zeezer, Commented Jun 19, 2012 at 6:17

Bill · Accepted Answer · 2012-06-19 20:36:44Z

1

If you want to maintain the Anonymous type you can use the InternalsVisibleToAttribute to allow a separate common library to work with the anonymous type.

I have done this previously to make a generic filtering library for datagrids with EF data sources, but it does involve a level of reflection and building the expression out of generic System.Linq.Expression components so this may not be worthwhile unless you have very many instances you want to do this to.

See msdn info:

http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.internalsvisibletoattribute.aspx

and

http://msdn.microsoft.com/en-us/library/system.linq.expressions.expression.aspx

If the select pattern is more predicable you may not need the expression portion, but in that case it may ultimately be simpler to just use a public class instead of the anonymous one.

Edit: "cannot convert anonymous to x" type errors mean you haven't gotten rid of the anonymous entirely/correctly.

In each of the locations you have new { ...whatever... } you are creating an anonymous type. If you create classes for each of those that have the correct properties to match what you are assigning then you just change something that looks like

new {x=1,y=2}

to read

new somenewclass() {x=1,x=2}

assuming you have defined elsewhere

public class somenewclass
{
    public int x {get;set;}
    public int y {get;set;}
}

edited Jun 19, 2012 at 20:36

answered Jun 18, 2012 at 14:35

Bill

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2 Comments

Zeezer Over a year ago

yes I will try defining a public class instead. But i get all kinds of error messages when I try to create a class instead, saying cannot implicitly convert from anonymous type to my class

Zeezer Over a year ago

Not exactly the answer i was looking for, but you helped me on the right track, so i accept this as answer

Furqan Hameedi · Accepted Answer · 2012-06-18 14:19:56Z

0

You can do like this ,

  var Query = commonFilter.Select(g => new
            {
                Year = g.Key.Year,
                Month = g.Key.Month,
                Day= g.Key.Day,
                TotErr = g.Count(),

                column1 = g.Sum(o => o.Process.Contains("something") ? 1 : 0),
                column2= g.Sum(o => o.Process.Contains(".something1") ? 1 : 0),
                column3= g.Sum(o => o.Process.Contains(".something2") ? 1 : 0),
                column4= g.Sum(o => o.Process.Contains("something3") ? 1 : 0),
                column5= g.Sum(o => o.Process.Contains(".something4") ? 1 : 0),
                column6 = g.Sum(o => o.Process.Contains(".something5") ? 1 : 0),
                column7= g.Sum(o => o.Process.Contains(".something6") ? 1 : 0),
                column8= g.Sum(o => o.Process.Contains(".something7") ? 1 : 0),
                column9= g.Sum(o => o.Process.Contains(".something8") ? 1 : 0),

                NumOrgs = g.Select(l => l.OrganizationId).Distinct().Count(),
                NumUsers = g.Select(l => l.UserId).Distinct().Count(),

            });
    if (request.Equals("some text"))
    {
        var filter = Query.GroupBy(x => new
            {
                x.Timestamp.Year,
                x.Timestamp.Month,
            }) ;
    }
    //Same thing again but slightly different
    else if (request.Equals("some other text"))
    {
        var filter = Query.GroupBy(x => new
            {
                x.Timestamp.Year,
                x.Timestamp.Month,
                x.Timestamp.Day
            });
    }

answered Jun 18, 2012 at 14:19

Furqan Hameedi

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2 Comments

Zeezer Over a year ago

nice idea, but couldnt get it to work. How could the variable query in your example, evaluate for example Year= g.Key.Year, when the grouping hasent even been declared yet?

Furqan Hameedi Over a year ago

My bad, I missed that point in a glitch, but at least it can be a starting point and can be refined further.

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