Question

我有一个名为：AttachmentType的实体，其属性ShowDuringRegistration为byte

执行此行我总是看到这个错误：指定的强制转换无效，无论我发送一个字节作为参数

Repository<AttachmentType>.FindBySpecification(new AttachmentSearchSpecification()
    .WithTraceCodeOrNationalNumber(traceCodeString)
    .WithAttachmentTypeShowDuringRegistration(false))
    .Select(p=>new attachmentTypeModel()
     {
       Id=p.Id,
       Title=p.Title
     })
    .ToList();

 public AttachmentSearchSpecification WithAttachmentTypeShowDuringRegistration(bool showDuringRegistration=false)
 {          
      AddExpression(p => p.AttachmentType.ShowDuringRegistration == (showDuringRegistration ? 1 : 0));
      return this;
 }

即使我向WithAttachmentTypeShowDuringRegistration方法发送一个字节并将ShowDuringRegistration与该属性进行比较它也不起作用

byte b=0;
Repository<AttachmentType>.FindBySpecification(new AttachmentSearchSpecification()
    .WithTraceCodeOrNationalNumber(traceCodeString)
    .WithAttachmentTypeShowDuringRegistration(b))
    .Select(p=> new attachmentTypeModel()
     {
       Id=p.Id,
       Title=p.Title
     })
    .ToList();

public AttachmentSearchSpecification WithAttachmentTypeShowDuringRegistration(byte showDuringRegistration)
{
    AddExpression(p => p.AttachmentType.ShowDuringRegistration == showDuringRegistration)
    return this;
}

这是错误引发的时间：

select cast(count(*) as INT) 
as col_0_0_ from EmploymentRegistration.[Attachment]
attachment0_, EmploymentRegistration.[Demand] demand1_,
 EmploymentRegistration.[AttachmentType] attachment5_ where ttachment0_.DemandId=demand1_.DemandId 
 and demand1_.PersonId=person3_.PartyId and person3_.PartyId=birthcerti4_.PersonId and
 attachment0_.AttachmentTypeId=attachment5_.AttachmentTypeId 
 and (demand1_.TraceCode like ('%'+?+'%') or birthcerti4_.NationalNumber like ('%'+?+'%'))
 and   attachment5_.ShowDuringRegistration=?

内部异常：{"Specified cast is not valid."}

protected void AddExpression(Expression<Func<T, bool>> expression);  this method get an experssion and append that expression to the linq query 



 public class AttachmentTypeMap : ClassMap<AttachmentType>
{
    public AttachmentTypeMap()
    {
        Schema("EmploymentRegistration");

        Id(p => p.Id);//int identity

        Map(p => p.Title);//string

        Map(p => p.ShowDuringRegistration);//byte

        Map(p => p.ScriptName)
            .Length(100);

        References(p => p.EmploymentLicense);
    }
}`

通过执行这样一个更简单的查询：

 Repository<AttachmentType>.FindAll().Where(p=>p.ShowDuringRegistration==(byte)1).Tolist();

将会像这样生成选择cast（count（*）as INT）为col_0_0_ from EmploymentRegistration。[AttachmentType] attachment0_左外连接 EmploymentRegistration。 [就业许可]就业1_ on attachment0_.EmploymentLicenseId = employment1_.EmploymentLicenseId其中
attachment0_.ShowDuringRegistration =？

当我想通过

知道返回值的数量时

int _totalItems = Query.Count();  //Query is IQueryable<T>

我会再次看到错误

即使执行此查询，错误也会像以前一样提高：

//ShowDuringRegistration  is byte?
var data= Repository<AttachmentType>.Find(p => p.ShowDuringRegistration == 0)
                                    .ToList();
public interface IRepository<T> where T : class
{

   IQueryable<T> Find();

    IQueryable<T> Find(object id);

    IQueryable<T> FindBySpecification(ISpecification<T> specification);

    IQueryable<T> Find(Expression<Func<T, bool>> expression);

}


 public static class Repository<T> where T : class
{

private static IRepository<T> Current
    {
        get { return UnitOfWork.GetRepository<T>(); }
    }

 public static IQueryable<T> Find(Expression<Func<T, bool>> expression)
    {
        return Current.Find(expression);
    }

 public static IList<T> FindAll(Expression<Func<T, bool>> expression)
    {
        return Current.FindAll(expression);
    }

}

Answer 1

您实际上并未使用字节 - 您使用的是int。它通常适用于C＃，因为ShowDuringRegistration会被提升为int，然后进行比较。试试这个：

public AttachmentSearchSpecification WithAttachmentTypeShowDuringRegistration
    (bool showDuringRegistration=false)
{
    byte value = showDuringRegistration ? (byte) 1 : (byte) 0;

    AddExpression(p => p.AttachmentType.ShowDuringRegistration == value);
    return this;
}

指定的强制转换在将int转换为byte时无效

1 个答案: