Question: Generic and Param based Custom Type Methods Support

[joshidp]

Hello,

Thanks for the awesome work.

I'm using your lib to write json configurable rules. I want to used generic and param based custom type methods as Utility methods. Below is a sample json config snippet.

{"expression": "Utilities.ConvertToArray(\"xyz\",\"abc\")"}

and below is the method with param

 public static string[] ConvertToArray(params string[] values)
        {
            if (values == null)
            {
                return new string[0];
            }

            return values.ToArray();
        }

When I try to call DynamicExpressionParser.ParseLambda method with above expression it fails with an error saying "No method called ConvertToArray found in Utilities". Please not normal method without param works just fine.

I want to create an array but since that was not possible in the expression directly using your lib I tried using the Utility method.

Similarly, generic methods also doesn't work.

Please help in providing a solution.

Thanks

[JonathanMagnan]

Hello @joshidp ,

Depending on your requirement, I might recommend you our other library instead: https://eval-expression.net/

This library is not free (unless you use only the LINQ part), but allow you to do pretty much anything such as using static method that you have created (You will need to notify our library by Registering the type).

If the only method not supported you want is creating an array, we might add this in this library as we see a value here. However, if you want to go a lot deeper than this library System.Linq.Dynamic.Core will probably not allow it unless our other library (C# Eval Expression) which supports pretty much everything.

Let me know if all you are looking for is creating an array or not.

Best Regards,

Jon

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[StefH]

@joshidp This is possible.

You need to create a static class and a static method. And annotate that class with the DynamicLinqType attribute.

Utils class

[DynamicLinqType]
public static class Utils
{
    public static string[] ConvertToArray(string[] values)
    {
        if (values == null)
        {
            return new string[0];
        }

        return values.ToArray();
    }
}

Usage

public class X
{
  public string[] Values { get; set; }
}

var list = new[] { new X { }, new X { Values = new[] { "a", "b" } } }.AsQueryable();
var result = list.Select(config, "Utils.ConvertToArray(Values)").ToDynamicList<string[]>();

However, these helper methods can only work on Linq to Objects.
It's not possible to use this for Linq to Entities (SQL).

Please let me know if this works for you.

[joshidp]

Thanks @StefH for the reply.

If I use your example of Class X the solution works but if I try to use my example I still get an error "System.Linq.Dynamic.Core.Exceptions.ParseException: 'No applicable method 'ConvertToArray' exists in type 'Utils''
"

In you example, Values prop is already a string array but what I am trying to do is pass string param and get the array back. Show below

Utility class

[DynamicLinqType]
   public static class Utils
   {
       public static string[] ConvertToArray(params string[] values)
       {
           if (values == null)
           {
               return new string[0];
           }

           return values.ToArray();
       }
   }

Usage

  var externals = new Dictionary<string, object>
            {
                {"Users", false},
                {"x", new[] { "a", "b", "c" } },
                {"y", 2},
            };

            string query = "Utils.ConvertToArray(\"a\",\"b\")";
            LambdaExpression expression = DynamicExpressionParser.ParseLambda(null, query, externals);
            Delegate del = expression.Compile();
            var result = del.DynamicInvoke();

Please tell how this issue can be resolved.

Thanks! in advance.

[StefH]

I think the params is not supported, so you can only use string[] values or string value.
Maybe you could just use object value and determine if it's an string or string-array yourself?
But I think that passing \"a\",\"b\" will be detected as 2 separate parameters, and not a params-string-array.

[joshidp]

ok, Thanks.

For now I'm thinking to write overloaded methods to return string[], it should suffice for limited set of values.

public static string[] ConvertToArray(string value1, string value2)
public static string[] ConvertToArray(string value1, string value2, string value3)
public static string[] ConvertToArray(string value1, string value2, string value3, string value4)
public static string[] ConvertToArray(string value1, string value2, string value3, string value4, string value5)

Thanks

[JonathanMagnan]

Hello @joshidp ,

Thank @StefH for pointing us out the DynamicLinqType, we were not aware of it and seem to be very useful for plenty of scenarios.

The v1.1.3 has been released. The library should now support params parameter (You can pass it like in your example but cannot yet create an array such as new string[] { "a", "b" }).

Let us know if everything works as expected.

[StefH]

@JonathanMagnan

I think that the original method from @joshidp is still not recognized?

public static string[] ConvertToArray(params string[] values)
        {
            if (values == null)
            {
                return new string[0];
            }

            return values.ToArray();
        }

With

public class X
{
  public string[] Values { get; set; }
}

var list = new[] { new X { }, new X { Values = new[] { "a", "b" } } }.AsQueryable();
var result = list.Select(config, "Utils.ConvertToArray(Values)").ToDynamicList<string[]>();

Still throws:

Unhandled Exception: System.Linq.Dynamic.Core.Exceptions.ParseException: No applicable method 'ConvertToArray' exists in type 'Utils'

[JonathanMagnan]

You are right, we forget probably the most essential case!

The v1.1.5 has been released

[JimmyPandas]

@StefH @JonathanMagnan
Hi team, this library is really powerful and I'm really appreciate your awesome work and support. Discussion within this issue has helped me to figure out how to define own custom static function and apply it in dynamic linq to object. However, I am wondering if there is a way we can apply C# extension function.

[JonathanMagnan]

Hello @JimmyLzy ,

When you say C# extension function, you mean C# extension method right?

Unless I'm wrong, extension methods are not yet supported.

We will look if that's possible or not to support basic scenario at least.

[JimmyPandas]

@JonathanMagnan
Yeah I mean c# extension method here. My static function works fine in local. However, when code is installed in ubuntu-18 in cloud, I get exception System.Linq.Dynamic.Core.Exceptions.ParseException: Expression expected. Do you have any ideas what cause this exception?
Thank you,
Jimmy

[JonathanMagnan]

What do you mean @JimmyLzy by works fine in local.

Unless I'm wrong, the library doesn't support yet extension methods when I checked yesterday.