如何更换物业类型及其在表达式树

Question

我有一个类PersonDTO可空的DateTime属性值：

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

而在表示层的类：

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

在我的表我有两种方法负责创建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; 
    } 

另外我是usin g AutoMapper？其将一个Expression<Func<PersonViewModel, bool>>转换成Expression<Func<PersonDTO, bool>>。转换的代码如下所示：

// ... 
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; 
    } 

    //... 
} 

我的表情转换器看起来像：

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); 
    } 
} 

我需要以某种方式部分转换lambda表达式：person => person.Birthday > Convert(15.11.2016 00:00)（在这种情况下，人的类型为PersonViewModel和生日DateTime？）看起来像这样：person => person.Birthday > 20161115（在这种情况下，personDTO和生日类型int？）。没有这个问题，所有的东西都能正确地映射和工作我知道我需要深入树并做一些操作，但我无法理解如何以及在哪里应该这样做。

Answer 1

我会沿着SG适应二进制表达式的日期时间值：

class AutoMapVisitor<TSource, TDestination>: ExpressionVisitor 
{ 
    // your stuff 
    protected override Expression VisitBinary(BinaryExpression node) 
    { 
     var memberNode = IsBirthdayNode(node.Left) 
      ? node.Left 
      : IsBirthdayNode(node.Right) 
       ? node.Right 
       : null; 
     if (memberNode != null) 
     { 
      var valueNode = memberNode == node.Left 
       ? node.Right 
       : node.Left; 
      // get the value 
      var valueToChange = (int?)getValueFromNode(valueNode); 
      var leftIsMember = memberNode == node.Left; 
      var newValue = Expression.Constant(DataTypesExtensions.NullIntToNullDateTime(valueToChange, /*insert your format here */ "")); 
      var newMember = Visit(memberNode); 
      return Expression.MakeBinary(node.NodeType, leftIsMember ? newMember : newValue, leftIsMember ? newValue : newMember); // extend this if you have a special comparer or sg 
     } 
     return base.VisitBinary(node); 
    } 

    private bool IsBirthdayNode(Expression ex) 
    { 
     var memberEx = ex as MemberExpression; 
     return memberEx != null && memberEx.Member.Name == "Birthday" && memberEx.Member.DeclaringType == typeof(PersonViewModel); 
    } 

    private object getValueFromNode(Expression ex) 
    { 
     var constant = ex as ConstantExpression; 
     if (constant != null) 
      return constant.Value; 
     var cast = ex as UnaryExpression; 
     if (cast != null && ex.NodeType == ExpressionType.Convert) 
      return getValueFromNode(cast.Operand); 
     // here you can add more shortcuts to improve the performance of the worst case scenario, which is: 
     return Expression.Lambda(ex).Compile().DynamicInvoke(); // this will throw an exception, if you have references to other parameters in your ex 
    } 

} 

是相当具体，但你的想法，你可以把它你usecases更通用。

但我认为你的属性映射是错误的。在sql中你想使用int比较。以上是为你做的。当automapper改变你的属性时，它应该用新的生日（改变类型）替换旧的生日，而不用调用NullDateTimeToNullInt。上面的代码将处理类型更改以进行比较。如果你有匿名选择或其他地方的成员，你会仍然有一个问题，我相信...