如何在表达式树中替换属性类型及其值

我有一个具有Nullable DateTime属性的PersonDTO类：

public class PersonDTO
{
    public virtual long Id { get; set; }
    public virtual string Name { get; set; }
    // YYYYMMDD format
    public virtual Nullable<int> Birthday { get; set; }
}

和Presentation层中的一个类：

public class PersonViewModel
{
    public virtual long Id { get; set; }
    public virtual string Name { get; set; }
    public virtual Nullable<DateTime> Birthday { get; set; }
}

在我的表单上，我有两个方法负责创建 Expression<Func<PersonViewModel, bool>> 对象：

private Expression<Func<PersonViewModel, bool>> GetFilterExpression()
    {             
        Expression condition = null;
        ParameterExpression pePerson = Expression.Parameter(typeof(PersonViewModel), "person");
        //...
        if (dtpBirth.Format != DateTimePickerFormat.Custom)
        {
            Expression target = Expression.Property(pePerson, pePerson.Type.GetProperty("Birthday", typeof(DateTime?)));
            UnaryExpression date = Expression.Convert(Expression.Constant(dtpBirth.Value.Date), typeof (DateTime?));
            condition = (condition == null)
                    ? Expression.GreaterThan(target, date)
                    : Expression.And(condition, Expression.GreaterThan(target, date));
        }
        // Формируем лямбду с условием и возвращаем результат сформированного фильтра
        return condition != null ? Expression.Lambda<Func<PersonViewModel, bool>>(condition, pePerson) : null;
    }

我也在使用AutoMapper？将一个 Expression<Func<PersonViewModel, bool>> 转换为 Expression<Func<PersonDTO, bool>> . 转换代码如下：

// ...
Mapper.CreateMap<PersonViewModel, PersonDTO>()
              .ForMember(dto => dto.Birthday, opt => opt.MapFrom(model => model.BirthdaySingle.NullDateTimeToNullInt("yyyyMMdd")));
// ...
public static class DataTypesExtensions
{
    public static DateTime? NullIntToNullDateTime(this int? input, string format)
    {
        if (input.HasValue)
        {
            DateTime result;
            if (DateTime.TryParseExact(input.Value.ToString(), format, CultureInfo.InvariantCulture, DateTimeStyles.None, out result))
            {
                return result;
            }
        }
        return null;
    }

    //...
}

My Expression转换器如下所示：

public static Expression<Func<TDestination, TResult>> RemapForType<TSource, TDestination, TResult>(
        this Expression<Func<TSource, TResult>> expression)
    {
        var newParameter = Expression.Parameter(typeof(TDestination));

        var visitor = new AutoMapVisitor<TSource, TDestination>(newParameter);
        var remappedBody = visitor.Visit(expression.Body);
        if (remappedBody == null)
        {
            throw new InvalidOperationException("Unable to remap expression");
        }

        return Expression.Lambda<Func<TDestination, TResult>>(remappedBody, newParameter);
    }

public class AutoMapVisitor<TSource, TDestination> : ExpressionVisitor
{
    private readonly ParameterExpression _newParameter;
    private readonly TypeMap _typeMap = Mapper.FindTypeMapFor<TSource, TDestination>();

    public AutoMapVisitor(ParameterExpression newParameter)
    {
        _newParameter = newParameter;
    }

    protected override Expression VisitMember(MemberExpression node)
    {
        var propertyMaps = _typeMap.GetPropertyMaps();

        // Find any mapping for this member
        // Here I think is a problem, because if it comes (person.Birthday => Convert(16.11.2016 00:00:00)) it can't find it.
        var propertyMap = propertyMaps.SingleOrDefault(map => map.SourceMember == node.Member);
        if (propertyMap == null)
        {
            return base.VisitMember(node);
        }

        var destinationProperty = propertyMap.DestinationProperty;
        var destinationMember = destinationProperty.MemberInfo;

        // Check the new member is a property too
        var property = destinationMember as PropertyInfo;
        if (property == null)
        {
            return base.VisitMember(node);
        }

        // Access the new property
        var newPropertyAccess = Expression.Property(_newParameter, property);
        return base.VisitMember(newPropertyAccess);
    }
}

我需要以某种方式转换lambda表达式的一部分： person => person.Birthday > Convert(15.11.2016 00:00) （在这种情况下人是PersonViewModel和类型DateTime的生日？）看起来像： person => person.Birthday > 20161115 （在这种情况下，人是PersonDTO和生日类型为int？） . 没有这个问题，一切都映射和正常工作 . 我知道我需要深入到树中并进行一些操作，但我无法理解我应该如何以及在何处进行操作 .