using System;

using System.Linq.Expressions;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var list = new List<Person>

        {

            new Person

            {

                Name = "Tof",

                Age = 20

            },

            new Person

            {

                Name = "Ted",

                Age = 30

            }

        };

​

        Expression<Func<Person, bool>> filterName = GetFilterName();

        Expression<Func<Person, bool>> filterAge = GetFilterAge();

​

        Expression<Func<Person, bool>> expresion = EFCoreExpressionTreeHelper.AndExpression(filterName, filterAge);

        Func<Person, bool> predicate = expresion.Compile();

​

        var result = list.Where(predicate);

​

        Console.WriteLine(result.FirstOrDefault()?.Name);

​

​

    }

    public class Person

    {

        public string Name { get; set; } = string.Empty;

        public int Age { get; set; }

    }

    static Expression<Func<Person, bool>> GetFilterName()

    {

        return x => x.Name.StartsWith("T");

    }

​

    static Expression<Func<Person, bool>> GetFilterAge()

    {

        return x => x.Age > 25;

    }

​

    /// <summary>

    /// https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.query.replacingexpressionvisitor?view=efcore-6.0

    /// </summary>

    public static class EFCoreExpressionTreeHelper

    {

        public static Expression<Func<T, bool>> AndExpression<T>(Expression<Func<T, bool>> left, Expression<Func<T, bool>> right)

        {

            var visitor = new ParameterReplaceVisitor(right.Parameters[0], left.Parameters[0]);

            var rewrittenRight = visitor.Visit(right.Body);

            var andExpression = Expression.AndAlso(left.Body, rewrittenRight);

​

            return Expression.Lambda<Func<T, bool>>(andExpression, left.Parameters);

        }

​

        private class ParameterReplaceVisitor : ExpressionVisitor

        {

            public ParameterReplaceVisitor(ParameterExpression target, ParameterExpression replacement)

            {

                Target = target;

                Replacement = replacement;

            }

​

            public ParameterExpression Target { get; private set; }

​

            public ParameterExpression Replacement { get; private set; }

​

            protected override Expression VisitParameter(ParameterExpression node)

            {

                return node == Target ? Replacement : base.VisitParameter(node);

            }

        }

    }

}