如何在成员表达式内部将datetime值转换为ToLocalTime

Question

我有一个成员表达式(类型为System.Linq.Expressions.MemberExpression｛System.Linq.Ixpressions.PropertyExpression｝(

我需要比较；"天"；以及"；月份"；将该表达式的DateTime值转换为Today’s Day/Month，但是在将我的表达式的值转换为LocalTime之后。我以UTC时间从数据库中检索它，在进行表达式比较之前，我需要将其转换为LocalTime。

我一直在努力寻找一种方法；ToLocalTime"；在表达式上，但我只得到错误，下面是我的最新试验：

DateTime today = DateTime.UtcNow.ToLocalTime();
//create expressions for day and month
var todayDayExp = Expression.Constant(today.Day);
var todayMonthExp = Expression.Constant(today.Month);
MemberExpression valueToChange = //code that returns memberexpression
//Problem is in line below
var ExpressionValueAfterToLocalTime = Expression.Call(typeof(DateTime), "ToLocalTime", null, valueToChange );
var valueprop = Expression.Property(ExpressionValueAfterToLocalTime , "Value");
var xconnectDayValue = Expression.Property(valueprop, "Day");
var xconnectMonthValue = Expression.Property(valueprop, "Month");

Expression dayComparisonExpression = Expression.Equal(
xconnectDayValue, todayDayExp);
Expression monthComparisonExpression = Expression.Equal(
xconnectMonthValue, todayMonthExp);
Expression finalEx = Expression.AndAlso(dayComparisonExpression, monthComparisonExpression);

我在尝试获取ExpressionValueAfterToLocalTime的行上出现错误："类型"System.DateTime"上不存在方法"ToLocalTime"；

有人知道如何做到这一点吗？我需要做"；ToLocalTime"；在成员表达式的DateTime值上。

Answer 1

好的，所以我找到了如何将MemberExpression类型的UTC DateTime对象转换为本地时间：

var dateTimeValueMemberExpression = //custom function that gets my datetime member expression
//gets the value property from my member expression
var valueprop = Expression.Property(dateTimeValueMemberExpression , "Value");
//create "MethodInfo" separately to use in the "Expression.Call" function
MethodInfo methodInfo = typeof(DateTime).GetMethod("ToLocalTime");

var valueToLocalTimeMethodCallExp = Expression.Call(valueprop, methodInfo);

一旦我得到了"；valueToLocalTimeMethodCallExp"；我能够访问它的"；"天"；以及"；月份"；属性如下：

var xconnectDayValue = Expression.Property(valueToLocalTimeMethodCallExp, "Day");
var xconnectMonthValue = Expression.Property(valueToLocalTimeMethodCallExp, "Month");