Question

我正在使用NPoco从我的数据库进行对象映射。我有以下实体：

public abstract class NamedEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Person : NamedEntity
{
    public Office Office { get; set; }
}

public class Office : NamedEntity
{
    public Address Address { get; set; }
    public Organisation ParentOrganisation { get; set; }
}

public class Address
{
     public string AddressLine1 { get; set; }
}

public class Organisation : NamedEntity
{
}

我在我的存储库中使用NPoco检索对象：

var people = Context.Fetch<Person, Office, Address, Organisation>(sql);

这是正常的，除了Person没有Office的情况，在这种情况下，sql查询中LEFT JOIN的结果为Office返回null，地址和组织列。

在这种情况下，NPoco中会抛出未处理的异常：

System.Reflection.TargetInvocationException: 
Exception has been thrown by the target of an invocation. 
---> System.NullReferenceException: 
Object reference not set to an instance of an object.
at poco_automapper(Person , Office , Address , Organisation )
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
at System.Delegate.DynamicInvokeImpl(Object[] args)
at NPoco.MultiPocoFactory.CallCallback[TRet](Delegate callback, IDataReader dr, Int32 count)
at NPoco.MultiPocoFactory.<>c__DisplayClassa`1.<CreateMultiPocoFactory>b__9(IDataReader reader, Delegate arg3)
at NPoco.Database.<Query>d__14`1.MoveNext()

有办法处理这种情况吗？或者我是否必须使用扁平化对象或单独的数据库调用？

Answer 1

这已在NPoco 2.2.40中修复感谢您报告。

Answer 2

尝试创建构造函数来初始化对象：

public abstract class NamedEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Person : NamedEntity
{
    public Person()
    {
        Office = new Office();
    }
    public Office Office { get; set; }
}

public class Office : NamedEntity
{
    public Office()
    {
        Address = new Address();
        ParentOrganisation = new Organisation();
    }
    public Address Address { get; set; }
    public Organisation ParentOrganisation { get; set; }
}

public class Address
{
    public string AddressLine1 { get; set; }
}

public class Organisation : NamedEntity
{
}

如何处理可能为null的嵌套NPoco对象？

2 个答案: