实体框架到 json - 分组数据

Question

我有一个名为 Client 的类，如下所示：

public class Client
{

    [Key, ForeignKey("BaseAssignments")]
    public int ClientId { get; set; }
    public string Owner { get; set; }
    public string CompanyName { get; set; }

    public virtual ICollection<BaseAssignment> BaseAssignments { get; set; }
}

还有一个名为 Base 的类，如下所示：

public class Base
{
    [Key, ForeignKey("BaseAssignments")]
    public int BaseId { get; set; }
    public string BaseName { get; set; }
    public DateTime BaseStart { get; set; }
    public DateTime BaseEnd { get; set; }

    public virtual ICollection<BaseAssignment> BaseAssignments { get; set; }
}

它们将与另一个名为 BaseAssignment 的类连接：

public class BaseAssignment
{
    [Key]
    public int BaseAssignmentId { get; set; }
    public int BaseId { get; set; }
    public int ClientId { get; set; }

    public virtual Base Base { get; set; }
    public virtual Client Client { get; set; }
}

这个想法是一个客户可以分配到多个基地，一个基地可以包含许多客户。

展望未来，我正在尝试以这样的方式序列化基础实体，即基础的 json 表示将其所有客户端的集合作为子对象。我试图实现的 Web Api 方法是：

db.Configuration.ProxyCreationEnabled = false;
var query = from b in db.Bases
    group b by b.BaseId into nb
    join ba in db.BaseAssignments on nb.FirstOrDefault().BaseId equals ba.BaseId
    join c in db.Clients on ba.ClientId equals c.ClientId
    select new BaseDTO
    {
        BaseName = nb.FirstOrDefault().BaseName,
        BaseStart = nb.FirstOrDefault().BaseStart,
        BaseEnd = nb.FirstOrDefault().BaseEnd,
        Clients = from c1 in db.Clients select new ClientDTO
        {
            ClientId = c1.ClientId,
            CompanyName = c1.CompanyName,
            Owner = c1.Owner
        }
    };
return query;

BaseDTO 如下所示：

public class BaseDTO
{
    public String BaseName { get; set; }
    public DateTime BaseStart { get; set; }
    public DateTime BaseEnd { get; set; }

    public IQueryable<ClientDTO> Clients { get; set; }
}

和 ClientDTO 看起来像：

public class ClientDTO
{
    public int ClientId { get; set; }
    public string Owner { get; set; }
    public string CompanyName { get; set; }
}

到目前为止，我收到一条错误消息，指出 ClientDTO 是一种意外类型。我能做些什么来解决这个问题，或者我选择的方式可能是完全错误的？提前感谢您对此的任何见解。

编辑

我对 Web Api 控制器方法进行了一些更改，所以它看起来像：

db.Configuration.ProxyCreationEnabled = false;
var query = from b in db.Bases
    group b by b.BaseId into nb
    join ba in db.BaseAssignments on nb.FirstOrDefault().BaseId equals ba.BaseId
    join c in db.Clients on ba.ClientId equals c.ClientId
    select new BaseDTO
    {
        BaseName = nb.FirstOrDefault().BaseName,
        BaseStart = nb.FirstOrDefault().BaseStart,
        BaseEnd = nb.FirstOrDefault().BaseEnd,
        Clients = new ClientDTO
        {
            ClientId = c.ClientId,
            CompanyName = c.CompanyName,
            Owner = c.Owner
        }
    };
return query;

这使得 Api 生成一个 JSON，但它仍然包含每个客户端的单个对象，而不是每个基。

Answer 1

基于StriplingWarrior's 的建议，将两全其美：

from b in db.Bases
select new BaseDTO
{
    BaseName = b.BaseName,
    BaseStart = b.BaseStart,
    BaseEnd = b.BaseEnd,
    Clients =
        from ba in b.BaseAssignments 
        join c in db.Clients on ba.ClientId equals c.ClientId
        select new ClientDTO
        {
            ClientId = c.ClientId,
            CompanyName = c.CompanyName,
            Owner = c.Owner
        }
 };

得到了我想要的 JSON - 谢谢。

Answer 2

您不必为此手动分组或加入任何东西，只需使用子选择并让 LINQ 完成繁重的工作。

from b in db.Bases
select new BaseDTO
{
    BaseName = b.BaseName,
    BaseStart = b.BaseStart,
    BaseEnd = b.BaseEnd,
    Clients = 
        from ba in b.BaseAssignments
        from c in ba.Client
        select new ClientDTO
        {
            ClientId = c.ClientId,
            CompanyName = c.CompanyName,
            Owner = c.Owner
        }
}