C# 好用的Expression动态拼接帮助类

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public static class ExpressionHandle {     /// <summary>     /// Linq的And操作     /// </summary>     /// <typeparam name="T"></typeparam>     /// <param name="first"></param>     /// <param name="second"></param>     /// <param name="tf">是否拼接param>     /// <returns>val为空就返回first，否则返回first与second的And操作</returns>     public static Expression<Func<T, bool>> IfAnd<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second, bool tf)     {         if (tf)         {             return first.ExpressionAnd(second);         }         return first;     }       /// <summary>     /// Linq的Or操作     /// </summary>     /// <typeparam name="T"></typeparam>     /// <param name="first"></param>     /// <param name="second"></param>     /// <param name="tf">是否为拼接</param>     /// <returns>val为空就返回first，否则返回first与second的Or操作</returns>     public static Expression<Func<T, bool>> IfOr<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second, bool tf)     {         if (tf)         {             return first.ExpressionOr(second);         }         return first;     }       /// <summary>     /// Linq的And操作     /// </summary>     /// <typeparam name="T"></typeparam>     /// <param name="first"></param>     /// <param name="second"></param>     /// <param name="tf">是否拼接param>     /// <returns>val为空就返回first，否则返回first与second的And操作</returns>     public static Expression<Func<T1, T2, bool>> IfAnd<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second, bool tf)     {         if (tf)         {             return first.ExpressionAnd(second);         }         return first;     }       /// <summary>     /// Linq的Or操作     /// </summary>     /// <typeparam name="T"></typeparam>     /// <param name="first"></param>     /// <param name="second"></param>     /// <param name="tf">是否为拼接</param>     /// <returns>val为空就返回first，否则返回first与second的Or操作</returns>     public static Expression<Func<T1, T2, bool>> IfOr<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second, bool tf)     {         if (tf)         {             return first.ExpressionOr(second);         }         return first;     }       /// <summary>     /// Linq的And操作     /// </summary>     /// <typeparam name="T"></typeparam>     /// <param name="first"></param>     /// <param name="second"></param>     /// <param name="tf">是否拼接param>     /// <returns>val为空就返回first，否则返回first与second的And操作</returns>     public static Expression<Func<T1, T2, T3, bool>> IfAnd<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second, bool tf)     {         if (tf)         {             return first.ExpressionAnd(second);         }         return first;     }       /// <summary>     /// Linq的Or操作     /// </summary>     /// <typeparam name="T"></typeparam>     /// <param name="first"></param>     /// <param name="second"></param>     /// <param name="tf">是否为拼接</param>     /// <returns>val为空就返回first，否则返回first与second的Or操作</returns>     public static Expression<Func<T1, T2, T3, bool>> IfOr<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second, bool tf)     {         if (tf)         {             return first.ExpressionOr(second);         }         return first;     } }

　　

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public static class ExpressionHelper {     private static Expression<T> Combine<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)     {         var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);         var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);         return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);     }     /// <summary>     /// And合并     /// </summary>     /// <returns></returns>     public static Expression<Func<T, bool>> ExpressionAnd<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)     {         return first.Combine(second, Expression.And);     }     /// <summary>     /// OR合并     /// </summary>     /// <returns></returns>     public static Expression<Func<T, bool>> ExpressionOr<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)     {         return first.Combine(second, Expression.Or);     }     /// <summary>     /// And合并     /// </summary>     /// <returns></returns>     public static Expression<Func<T1, T2, bool>> ExpressionAnd<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second)     {         return first.Combine(second, Expression.And);     }     /// <summary>     /// OR合并     /// </summary>     /// <returns></returns>     public static Expression<Func<T1, T2, bool>> ExpressionOr<T1, T2>(this Expression<Func<T1, T2, bool>> first, Expression<Func<T1, T2, bool>> second)     {         return first.Combine(second, Expression.Or);     }     /// <summary>     /// And合并     /// </summary>     /// <returns></returns>     public static Expression<Func<T1, T2, T3, bool>> ExpressionAnd<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second)     {         return first.Combine(second, Expression.And);     }     /// <summary>     /// OR合并     /// </summary>     /// <returns></returns>     public static Expression<Func<T1, T2, T3, bool>> ExpressionOr<T1, T2, T3>(this Expression<Func<T1, T2, T3, bool>> first, Expression<Func<T1, T2, T3, bool>> second)     {         return first.Combine(second, Expression.Or);     } }

　　

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public class ParameterRebinder : ExpressionVisitor {     private readonly Dictionary<ParameterExpression, ParameterExpression> map;     /// <summary>     ///     /// </summary>     /// <param name="map"></param>     public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)     {         this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();     }     /// <summary>     ///     /// </summary>     /// <param name="map"></param>     /// <param name="exp"></param>     /// <returns></returns>     public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)     {         return new ParameterRebinder(map).Visit(exp);     }     /// <summary>     ///     /// </summary>     /// <param name="p"></param>     /// <returns></returns>     protected override Expression VisitParameter(ParameterExpression p)     {         ParameterExpression replacement;         if (map.TryGetValue(p, out replacement))         {             p = replacement;         }         return base.VisitParameter(p);     }   }