Question

我正在尝试编写一个将投影到DTO的查询，其中两个属性是int数组。由于投影中的ToArray（）调用，我收到错误。

teams = context
  .Teams
  .Include("TeamDepartments")
  .Include("TeamEmployees")
  .Select(t => new TeamDto
      {
          sourceSystemId = t.TeamId,
          name = t.Name,
          manager = t.EmployeeIdTeamManager,
          teamLead = t.EmployeeIdTeamLead,
          employees = t.TeamEmployees.Select(te => te.EmployeeId).ToArray(),
          departments = t.TeamDepartments.Select(td => td.DepartmentId).ToArray()
       })
  .ToList();

对于两个int []属性的员工和部门，如何获取这些值？现在，我只是撤回团队列表，然后循环遍历它们以创建DTO。

我见过其他类似的问题，但解决方案对我来说似乎没有用。我怀疑我需要采取额外的步骤，因为我正在穿越一段关系。

Answer 1

您需要做的是将此查询分为两个不同的步骤;第一个将检索正确的结果，第二个将数据投影到您的DTO。像这样：

teams = context
  .Teams
  .Include("TeamDepartments")
  .Include("TeamEmployees")
  .Select(t => new // notice this is an anonymous object
      {
          sourceSystemId = t.TeamId,
          name = t.Name,
          manager = t.EmployeeIdTeamManager,
          teamLead = t.EmployeeIdTeamLead,
          employees = t.TeamEmployees.Select(te => te.EmployeeId),
          departments = t.TeamDepartments.Select(td => td.DepartmentId)
       })
  .ToList() // first run the query on the server without the ToArray calls
  .Select(obj => new TeamDto
      {     // then project the in-memory results onto your DTO.
          sourceSystemId = obj.sourceSystemId,
          name = obj.name,
          manager = obj.manager,
          teamLead = obj.teamLead,
          employees = obj.employees.ToArray(),
          departments = obj.departments.ToArray()
      })
  .ToList();

Answer 2

我认为问题在于您尝试在SQL提供程序转换为SQL查询的块中调用ToArray。当然，SQL Server不知道数组是什么，所以方法不起作用。如果您删除ToArray电话会怎样？我相信这些结果会以IEnumberables的形式返回到该块之外，您可以根据需要进行转换。我不确定这会有效，但如果您通过以下方式更改TeamDto定义，则可能会解决问题。

 // you have now something like
 string[] employees;
 // instead do
 IEnumberable<string> employees;
 // If you want an array add
 string[] _employees;

然后在_employees = employees.ToArray();

的查询之外

LINQ to Entities无法识别ToArray

2 个答案: