// C# Eval Expression

// Doc: https://eval-expression.net/options

​

// @nuget: Z.Expressions.Eval

​

/*

## DynamicGetMemberMissingValueFactory

​

The DynamicGetMemberMissingValueFactory option lets you get or sets a factory to return a value when a member is not found from an entity or ExpandoObject. In other words, it allows specifying a value for a missing member on demand. By default, the DynamicGetMemberMissingValueFactory value is null.

​

In this example, we will first set our DynamicGetMemberMissingValueFactory option, then use it with an entity customer, and after use it again with an ExpandoObject. In both cases, we will try to retrieve the member `FullName`, which doesn't exist but still return a value correctly due to the missing member factory previously set.

​

See more: https://eval-expression.net/options

*/

​

using System;

using System.Collections.Generic;

using System.Dynamic;

using Z.Expressions;

​

public class Program

{

    public static void Main()

    {

        // Global Context: EvalManager.DefaultContext.DynamicGetMemberMissingValueFactory = (obj, propertyOrFieldName) => { };

        var context = new EvalContext();

        context.DynamicGetMemberMissingValueFactory = (obj, propertyOrFieldName) =>

        {

            if(obj is Customer customer && propertyOrFieldName == "FullName")           

            {       

                // resolution for `Customer`

                return $"{customer.FirstName} {customer.LastName}";

            }

            else

            {

                // resolution for `ExpandoObject`

                dynamic expando = obj;

                return $"{expando.FirstName} {expando.LastName}";

            }

            throw new Exception("Not found");

        };

​

        // Entity

        {

            var customer = new Customer();

            customer.FirstName = "C# Eval";

            customer.LastName = "Expression";

​

            var r1 = context.Execute("customer.FullName", new { customer });

            Console.WriteLine("1 - Result: " + r1);

        }

​

        // ExpandoObject

        {

            dynamic customer = new ExpandoObject();

            customer.FirstName = "ZZZ";

            customer.LastName = "Projects";

​

            var r1 = context.Execute("customer.FullName", new { customer });

            Console.WriteLine("1 - Result: " + r1);

        }

    }

    public class Customer

    {

        public string FirstName;

        public string LastName;

    }

}