.net5 Expression扩展

    public static class ExpressionEx
    {
        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.OrElse);
            return one.Compose(another, Expression.Or);
        }

        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;
            }
        }
    }