LinqDynamicQueryHelper.cs

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;

namespace Common
{

/// <summary>

/// 统一ParameterExpression

    /// </summary>
    class ParameterReplacer : ExpressionVisitor
    {

public ParameterReplacer(ParameterExpression paramExpr)
{

this.ParameterExpression = paramExpr;
}

public ParameterExpression ParameterExpression { get; private set; }

        public Expression Replace(Expression expr)
        {
            return this.Visit(expr);
        }

        protected override Expression VisitParameter(ParameterExpression p)
        {
            return this.ParameterExpression;
        }
    }

public static class PredicateExtensionses
{

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<Func<T, bool>> And<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
{

var candidateExpr = Expression.Parameter(typeof(T), "candidate");

var parameterReplacer = new ParameterReplacer(candidateExpr);

var left = parameterReplacer.Replace(exp_left.Body);

var right = parameterReplacer.Replace(exp_right.Body);

            var body = Expression.And(left, right);
            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");

var parameterReplacer = new ParameterReplacer(candidateExpr);

var left = parameterReplacer.Replace(exp_left.Body);

var right = parameterReplacer.Replace(exp_right.Body);

var body = Expression.Or(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }
    }

    //public static class LinqDynamicQueryHelper
    //{
    //    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<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
// {

// var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());

// return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);
// }

// public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
// {

// var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());

// return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);

// }

//}
}
转自：21使用WCF_RIA实现分页和动态多条件查询