Linq输出作为接口?

时间:2020-03-06 14:43:47  来源:igfitidea点击:

这是我要尝试执行的代码:

public IList<IOperator> GetAll()
{
      using (var c = new MyDataContext())
      {
          return c.Operators.ToList();
      }
}

操作员实现IOperator,但出现以下编译错误:

Cannot implicitly convert type 'System.Collections.Generic.List<MyProject.Core.Operator>' to 'System.Collections.Generic.IList<MyProject.Core.Model.IOperator>'. An explicit conversion exists (are you missing a cast?)

我该如何投放才能获得所需的东西?

解决方案

尝试Cast &lt;>()方法:

return c.Operators.Cast<IOperator>().ToList();

编辑:其实,

返回(List <IOperator>)c.Operators.ToList();

不会成功的对不起

如果我将代码更改为以下内容:

public IList<IOperator> GetAll()
{
      using (var c = new MyDataContext())
      {
           var operators = (from o in c.Operators
                            select o).Cast<IOperator>();

           return operators.ToList();
      }
}

它不仅可以编译,而且可以正常工作!感谢我们朝着正确的方向前进。

使用ConvertAll <>

http://msdn.microsoft.com/en-us/library/kt456a2y.aspx

例如:在这种情况下,TEntity必须是IBusinessUnit,但是是一个类,因此我将将List <Operator>转换为List <IOperator>时遇到同样的麻烦(假设操作员实现IOperator)。

就我们而言,就像我们说的那样,Operator不会妨碍IOperator,但这没关系,它仍然可以工作-

public static IList<IBusinessUnit> toIBusinessUnitIList(List<TEntity> items)
      {

      return items.ConvertAll<IBusinessUnit>(new Converter<TEntity, IBusinessUnit>(TEntityToIBuisinessUnit));
      }

  /// <summary>
  /// Callback for List<>.ConvertAll() used above.
  /// </summary>
  /// <param name="md"></param>
  /// <returns></returns>
  private static IBusinessUnit TEntityToIBuisinessUnit(TEntity te)
  {
   return te;  // In your case, do whatever magic you need to do to convert an Operator to an IOperator here.
  }