C#动态拼接lambda表达式

拼接帮助类

  #region 动态拼接lambda表达式

    /// 

    /// Lambda表达式拼接扩展类
    /// 
    public static class Utility
    {
        /// 

        /// Lambda表达式拼接
        /// 
        /// 
        /// 
        /// 
        /// 
        /// 
        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
        {
            // 构建参数映射（从第二个参数到第一个参数）
            var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
            // 将第二个lambda表达式中的参数替换为第一个lambda表达式的参数
            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
            // 将lambda表达式体的组合应用于第一个表达式中的参数
            return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
        }
        /// 

        /// and扩展
        /// 
        /// 
        /// 
        /// 
        /// 
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.AndAlso);
        }
        /// 

        /// or扩展
        /// 
        /// 
        /// 
        /// 
        /// 
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.OrElse);
        }
    }
    /// 

    /// 
    /// 
    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);
        }
    }
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调用方法：

 Expression<Func<OrderDO, bool>> expression=t=>true;

            expression=expression.And(t => t.orderStartTime > start && t.orderStartTime < end);
            if (!string.IsNullOrWhiteSpace(orderid))
            {
                expression= expression.And(t => t.OrderID == orderid);
            }  
            if (!string.IsNullOrWhiteSpace(BatchID))
            {
                expression= expression.And(t => t.BatchNo == BatchID);
            } 
            if(!string.IsNullOrWhiteSpace(deliver))
            {
                expression= expression.And(t => t.deliveryBillNo == deliver);
            } 
            if(!string.IsNullOrWhiteSpace(UserTel))
            {
                expression= expression.And(t => t.buyerMobile == UserTel);
            }
            if(string.IsNullOrWhiteSpace(orderid)&&string.IsNullOrWhiteSpace(BatchID)&&string.IsNullOrWhiteSpace(deliver)&&string.IsNullOrWhiteSpace(UserTel))
            {
                expression= expression.And(t => (orderstatus == t.ApproveStatus || orderstatus == 0)&& (supplierid == t.supplierid || supplierid == 0)&& (ordertype == t.orderType || ordertype == 0));
            }
            orders= SqlsugarHelper.Init().GetClient().Queryable<OrderDO>().AS("Erp_Order_Info")
                        .Where(expression).OrderByDescending(item => item.orderStartTime)
                .ToPageList(page, limit, ref totalcount);

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