using System;

using System.Linq;

using System.Linq.Expressions;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    private static IQueryable<Data> GetData()

    {

        return null;

    }

    private static string[] Codes = new string[] { "ALPHA", "BETA" };

    private static IQueryable<Data> BaseQuery()

    {

        IQueryable<Data> query = GetData();

​

        Expression<Func<Data, bool>> expression = x=>false;

        foreach (var row in Codes)

            expression = expression.Or(t => t.Comp_Code == row.ToString());

        return query.Where(expression);

    }

}

​

public class Data

{

    public string Comp_Code { get; set; }

}

​

​

public static class ExpressionExt

{

    private class ParameterReplaceVisitor : ExpressionVisitor

    {

        public ParameterExpression Target { get; set; }

        public ParameterExpression Replacement { get; set; }

​

        protected override Expression VisitParameter(ParameterExpression node)

        {

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

        }

    }

    public static Expression<Func<T, bool>> Or<T>(

        this Expression<Func<T, bool>> left, Expression<Func<T, bool>> right)

    {

        var visitor = new ParameterReplaceVisitor()

        {

            Target = right.Parameters[0],

            Replacement = left.Parameters[0],

        };

​

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

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

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

    }

        public static Expression<Func<T, bool>> And<T>(

        this Expression<Func<T, bool>> left, Expression<Func<T, bool>> right)

    {

        var visitor = new ParameterReplaceVisitor()

        {

            Target = right.Parameters[0],

            Replacement = left.Parameters[0],

        };

​

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

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

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

    }

}