Func or Predicate to ExpressionTree

Question

Let's say I have:

 Func<Customer,bool > a = (c) => c.fullName == "John";

now i want to convert totree expression in any way to do this?

I know that I can define it from the first place as expressiontree, but I have a different situation, because I must first concatenate some lambda expressions and then pass them to a method that accepts the expression, which leads to a compile-time error!

Example:

        Func<Customer, bool> a = (c) => c.fullName == "John";
        Func<Customer, bool> b = (c) => c.LastName == "Smith";
        Func<Customer, bool> final = c => a(c) && b(c); 

now I want to pass final to a method that takes

ExpressionTree<Func<Customer,bool >>

it gives a compile time error

early

Answer 1

. Func<...> , , . .NET .

, , , : , . , , , .

. , , . , .

, , , :

Expression<Func<Customer, bool>> a = c => c.FullName == "John";
Expression<Func<Customer, bool>> b = c => c.LastName == "Smith";

var cp = Expression.Parameter(typeof(Customer), "c");

var ai = Expression.Invoke(a, cp);
var bi = Expression.Invoke(b, cp);

var final = Expression.Lambda<Func<Customer, bool>>(
    Expression.AndAlso(ai, bi), cp);

, AndAlso (&&); OrElse || ..

Answer 2

Func, .

:

Expression<Func<Customer, bool>> exprA = (c) => c.fullName == "John";
Func<Customer, bool> funcA = exprA.Compile();

.

Answer 3

, , :

Expression<Func<Customer, bool>> a = (c) => c.FullName == "John";
Expression<Func<Customer, bool>> b = (c) => c.LastName == "Smith";

var cp = Expression.Parameter(typeof(Customer), "c");

var ai = Expression.Invoke(a, cp);
var bi = Expression.Invoke(b, cp);

var final = Expression.Lambda<Func<Customer, bool>>(Expression.And(ai, bi), cp);

Answer 4

, , , . a Func<TInput, TOutput> Expression<Func<TInput, TOutput>>.

ElegantCode

Func:

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace ConsoleApplication1
{
    class Program
    {
        public static bool Method(Expression<Func<int, bool>> predicate, int value)
        {
            return predicate.Compile()(value);
        }

        static void Main(string[] args)
        {
            Func<int, bool> testPredicate = n => n == 1;
            var output = ConvertFuncToExpression(testPredicate);
            Console.WriteLine(Method(output, 3));
            Console.WriteLine(Method(output, 1));
        }

        private static Expression<TDelegate> CreateExpression<TDelegate>(MethodBase method)
        {
            var delegateArguments = typeof(TDelegate).GetMethod("Invoke").GetParameters().Select((parameter, index) => Expression.Parameter(parameter.ParameterType, "param_" + index)).ToArray();
            if (delegateArguments.Count() != method.GetParameters().Count()) throw new InvalidOperationException("The number of parameters of the requested delegate does not match the number parameters of the specified method.");

            var argumentsTypes = method.GetGenericArguments();
            argumentsTypes = (argumentsTypes.Length > 0) ? argumentsTypes : null;
            var convertedArguments = method.GetParameters().Select((parameter, index) => Expression.Convert(delegateArguments[index], parameter.ParameterType)).ToArray();
            var call = Expression.Call(method.DeclaringType, method.Name, argumentsTypes, convertedArguments);

            var lambda = Expression.Lambda<TDelegate>(call, delegateArguments);
            return lambda;
        }

        private static Expression<Func<TIn1, TOut>> ConvertFuncToExpression<TIn1, TOut>(Func<TIn1, TOut> input)
        {
            MethodInfo method = input.Method;
            return CreateExpression<Func<TIn1, TOut>>(method);
        }
    }
}