• c#表达式扩展与或非 通过表达式获取字段属性名称


     public static class ExpressionHelper
        {
            #region 与或非封装
            public static Expression<Func<T, bool>> True<T>() { return param => true; }
            public static Expression<Func<T, bool>> False<T>() { return param => false; }
    
            public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> one, Expression<Func<T, bool>> another)
            {
                //return one.Compose(another, Expression.AndAlso);
                return one.Compose(another, Expression.And);
            }
    
            public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> one, Expression<Func<T, bool>> another)
            {
                return one.Compose(another, Expression.Or);
                //return one.Compose(another, Expression.OrElse);
            }
    
            public static Expression<Func<T, bool>> Compose<T>(this Expression<Func<T, bool>> one, Expression<Func<T, bool>> another, Func<Expression, Expression, Expression> action)
            {
                //创建新参数
                var newParameter = Expression.Parameter(typeof(T));
    
                var parameterReplacer = new ParameterReplacer(newParameter);
                var left = parameterReplacer.Replace(one.Body);
                var right = parameterReplacer.Replace(another.Body);
    
                var body = action(left, right);
    
                return Expression.Lambda<Func<T, bool>>(body, newParameter);
            }
    
            /// <summary>
            /// 参数替换
            /// </summary>
            internal class ParameterReplacer : ExpressionVisitor
            {
                public ParameterReplacer(ParameterExpression paramExpr)
                {
                    Parameter = paramExpr;
                }
    
                //新的表达式参数
                private ParameterExpression Parameter { get; set; }
    
                public Expression Replace(Expression expr)
                {
                    return this.Visit(expr);
                }
    
                /// <summary>
                /// 覆盖父方法,返回新的参数
                /// </summary>
                /// <param name="p"></param>
                /// <returns></returns>
                protected override Expression VisitParameter(ParameterExpression p)
                {
                    return Parameter;
                }
            }
            #endregion
    
            /// <summary>
            /// 获取表达式调用的字段名称
            /// </summary>
            /// <typeparam name="T"></typeparam>
            /// <param name="expr"></param>
            /// <returns></returns>
            public static string GetPropertyName<T>(Expression<Func<T, object>> expr)
            {
                switch (expr.Body)
                {
                    case MemberExpression memberExpression:
                        return memberExpression.Member.Name;
                    case UnaryExpression unaryExpression:
                        if (unaryExpression.Operand is MemberExpression expression)
                        {
                            return expression.Member.Name;
                        }
    
                        break;
                    default:
                        break;
                }
    
                return "";
            }
        }
    
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  • 原文地址:https://www.cnblogs.com/ives/p/15727572.html
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