using System;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Expressions;

namespace HYS.Fee.AppSrv

{

    /// <summary>

    /// 数据库上下文

    /// </summary>

    public static class PredicateBuilder

    {

        public static Expression<Func<T, bool>> True<T>() { return f => true; }

        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)

        {

            // build parameter map (from parameters of second to parameters of first)

            var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);

            // replace parameters in the second lambda expression with parameters from the first

            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);

            // apply composition of lambda expression bodies to parameters from the first expression

            return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);

        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)

        {

            return first.Compose(second, Expression.And);

        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)

        {

            return first.Compose(second, Expression.Or);

        }

    }

    public class ParameterRebinder : ExpressionVisitor

    {

        private readonly Dictionary<ParameterExpression, ParameterExpression> map;

        public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)

        {

            this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();

        }

        public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)

        {

            return new ParameterRebinder(map).Visit(exp);

        }

        protected override Expression VisitParameter(ParameterExpression p)

        {

            ParameterExpression replacement;

            if (map.TryGetValue(p, out replacement))

            {

                p = replacement;

            }

            return base.VisitParameter(p);

        }

    }

}

Expression<Func<表名, bool>> expr = n => true;

expr = expr.And(n => n.PNAME.Contains(""));

expr = expr.Or(n => n.PID > );

context.表名.Where(expr).ToList()