c# - 带有poco生成的 Entity Framework IQueryable

Question

我创建了一个 T4 模板，它生成标准实体类及其每个属性的接口(interface)，这样我就可以制作仅包含我想要的数据的自定义 poco 对象。我还创建了一个复制函数，它可以在实现所述实体接口(interface)的任何对象之间进行转换

生成的代码如下所示

//------------------------------------------------------------------------------
// <auto-generated>
//    This code was generated from a template.
//
//    Manual changes to this file may cause unexpected behavior in your application.
//    Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

namespace DomainModel
{
    using System;
    using System.Collections.Generic;
    using System.Linq;


    public interface IRole
    {
    }
    public interface IRole_RoleId : IRole
    {
      int RoleId { get; set; }
    }
    public interface IRole_ApplicationName : IRole
    {
      string ApplicationName { get; set; }
    }
    public interface IRole_RoleName : IRole
    {
      string RoleName { get; set; }
    }
    public interface IRole_Description : IRole
    {
      string Description { get; set; }
    }

    public interface IRole_Users : IRole 
    {
      ICollection<IUser> Users { get; set; }
      IUser NewUsers();
    }

    public interface IRole__All : IRole_RoleId, 
      IRole_ApplicationName, 
      IRole_RoleName, 
      IRole_Description, 
      IRole_Users
    {
    }

    public partial class Role : IRole
    {
      public Role()
      {
        this.Users = new HashSet<User>();
      }

      public int RoleId { get; set; }
      public string ApplicationName { get; set; }
      public string RoleName { get; set; }
      public string Description { get; set; }

      public virtual ICollection<User> Users { get; set; }
    }

    public static class IRoleExt
    {
      public static T CopyTo<T>(this IRole src , T dest = null  )  where T : class, IRole, new()
      {
        dest = dest ?? new T();
        dest.Copy(src);
        return dest;
      }
      public static void Copy(this IRole dest, IRole src)
      {
        var ms = new MergeStack();
        Role role;
        if((role = dest as Role) != null){
          ms.TryCopy<IRole,Role>((indexCopy) => {return indexCopy(role);}, src);
        }
        else if ((role = src as Role) != null){
          ms.TryCopy<Role,IRole>((indexCopy) => {return indexCopy(dest);}, role);
        }
        else{
          ms.TryCopy<IRole,IRole>((indexCopy) => {return indexCopy(dest);}, src);
        }
        dest.Copy(src, ms);
      }

      internal static void Copy(this IRole dest,
        IRole src,
        MergeStack ms)
      {
        dest.Set_RoleId(src.Get_RoleId());
        dest.Set_ApplicationName(src.Get_ApplicationName());
        dest.Set_RoleName(src.Get_RoleName());
        dest.Set_Description(src.Get_Description());
        dest.Set_Users(src.Get_Users(),ms);
      }
        public static Nullable<int> Get_RoleId(this IRole src)
      {
        IRole_RoleId srcIRole_RoleId;
        if((srcIRole_RoleId = src as IRole_RoleId) != null )
        {
          return srcIRole_RoleId.RoleId;
        }
        Role role;
        if((role = src as Role) != null )
        {
          return role.RoleId;
        }
          return null;

      }
        public static void Set_RoleId(this IRole dest, Nullable<int> src)
      {
        IRole_RoleId destIRole_RoleId;
        if((destIRole_RoleId = dest as IRole_RoleId) != null)
        {
           destIRole_RoleId.RoleId = src.GetValueOrDefault();
            }
        Role role;
        if((role = dest as Role) != null )
        {
          role.RoleId = src.GetValueOrDefault();
        }
      }

        public static string Get_ApplicationName(this IRole src)
      {
        IRole_ApplicationName srcIRole_ApplicationName;
        if((srcIRole_ApplicationName = src as IRole_ApplicationName) != null )
        {
          return srcIRole_ApplicationName.ApplicationName;
        }
        Role role;
        if((role = src as Role) != null )
        {
          return role.ApplicationName;
        }
          return null;

      }
        public static void Set_ApplicationName(this IRole dest, string src)
      {
        IRole_ApplicationName destIRole_ApplicationName;
        if((destIRole_ApplicationName = dest as IRole_ApplicationName) != null)
        {
           destIRole_ApplicationName.ApplicationName = src;
            }
        Role role;
        if((role = dest as Role) != null )
        {
          role.ApplicationName = src;
        }
      }

        public static string Get_RoleName(this IRole src)
      {
        IRole_RoleName srcIRole_RoleName;
        if((srcIRole_RoleName = src as IRole_RoleName) != null )
        {
          return srcIRole_RoleName.RoleName;
        }
        Role role;
        if((role = src as Role) != null )
        {
          return role.RoleName;
        }
          return null;

      }
        public static void Set_RoleName(this IRole dest, string src)
      {
        IRole_RoleName destIRole_RoleName;
        if((destIRole_RoleName = dest as IRole_RoleName) != null)
        {
           destIRole_RoleName.RoleName = src;
            }
        Role role;
        if((role = dest as Role) != null )
        {
          role.RoleName = src;
        }
      }

        public static string Get_Description(this IRole src)
      {
        IRole_Description srcIRole_Description;
        if((srcIRole_Description = src as IRole_Description) != null )
        {
          return srcIRole_Description.Description;
        }
        Role role;
        if((role = src as Role) != null )
        {
          return role.Description;
        }
          return null;

      }
        public static void Set_Description(this IRole dest, string src)
      {
        IRole_Description destIRole_Description;
        if((destIRole_Description = dest as IRole_Description) != null)
        {
           destIRole_Description.Description = src;
            }
        Role role;
        if((role = dest as Role) != null )
        {
          role.Description = src;
        }
      }

      public static ICollection<IUser> Get_Users(this Role src)
      {
        return src.Users.Cast<IUser>().ToList();
        }
        public static ICollection<IUser> Get_Users(this IRole src)
      {
        IRole_Users srcIRole_Users;
        if((srcIRole_Users = src as IRole_Users) != null )
        {
          return srcIRole_Users.Users;
        }
        Role role;
        if((role = src as Role) != null )
        {
          return role.Get_Users();
        }
          return null;
      }
      public static void Set_Users(this IRole dest, ICollection<IUser> src)
      {
        var ms = new MergeStack();
        dest.Set_Users(src, ms);
      }

      internal static void Set_Users(this IRole dest, ICollection<IUser> src, MergeStack ms)
      {
        IRole_Users destIRole_Users;
        if((destIRole_Users = dest as IRole_Users) != null)
        {
          Func<IUser,IUser> iToIFunc = (x=> 
              ms.TryCopy<IUser,IUser>((indexCopy)=>
              {
                var ret = destIRole_Users.NewUsers();
                  var exists = indexCopy(ret);
                if(null != exists)
                    ret = exists;
                  else
                  ret.Copy(x,ms);
                return ret;
              },x));
          destIRole_Users.Users = (null !=src)?
          src.Select(iToIFunc).ToList():null;
        }

        Role role;
        if((role = dest as Role) != null)
        {
          Func<IUser,User> iToEFunc = (x=> 
              ms.TryCopy<IUser,User>((indexCopy)=>
              {
                var ret = new User();
                  var exists = indexCopy(ret);
                if(null != exists)
                    ret = exists;
                  else
                  ret.Copy(x,ms);
                return ret;
              },x));
          role.Users = (null !=src)?
          src.Select(iToEFunc).ToList():null;
        }
      }
    }
}

您看到的那个合并堆栈对象是一个跟踪器，因此我可以处理引用循环。看起来像这样

using System;
using System.Collections.Generic;
using System.Linq;

namespace DomainModel
{

    internal class MergeStack
    {
        private readonly Dictionary<Type, Dictionary<Object, Object>> _mergeObjDict = new Dictionary<Type, Dictionary<object, object>>();
        private readonly IList<Action> _registerActions = new List<Action>();

        public T TryCopy<TKey, T>(Func<Func<T, T>, T> func, TKey key) where T : class
        {
            if (key == null)
                return null;

            Func<T, T> act = (objToIndex) =>
            {
                Dictionary<object, object> objToObj;
                if (!_mergeObjDict.ContainsKey(objToIndex.GetType()))
                {
                    objToObj = new Dictionary<object, object>();
                    _mergeObjDict.Add(objToIndex.GetType(), objToObj);
                }
                else
                {
                    objToObj = _mergeObjDict[objToIndex.GetType()];
                }
                if (!objToObj.ContainsKey(key))
                {
                    objToObj.Add(key, objToIndex);
                }
                else
                {
                    return objToObj[key] as T;
                }
                return null as T;
            };
            return func(act);
        }
    }
}

现在所有这些都按预期正常工作，它成功地将所有已实现的属性复制到域模型/接口(interface)或从域模型/接口(interface)复制。

我现在正尝试使用 IQueryable 和延迟加载。

我现在正在做这个

dbContext.Roles.Select((x)=> x.CopyTo<RolesPoco>());

我想看看是否有一种方法可以自动生成包含，例如

dbContext.Roles.Select((x)=> x.Users.Include((y)=> y.someSubEntity);

我也想看看我是否可以加入一些像这样的 where 子句

//the first string is a path so something like "Roles.Users.someSubEntity"
//the second string is a IQueryable function like Where or Take
Dictionary<String,Dictionary<String,List<Func<T, IQueryable<TProperty>>>> queryDict

dbContext.Roles.Select((x)=> x.CopyTo<RolesPoco>(queryDict)

然后 List 将是一些可以在 include 函数内部运行的 lambda 列表。有人对此有任何想法吗？

编辑:我重构并简化了一些代码，这样即使类没有实现接口(interface)，它也可以调用 getter/setter。因此，无论是否存在支持字段，都可以访问属性。如果未定义，则返回 null。

Edit2:由于似乎不清楚我要实现的目标，让我澄清一下。如果您查看此 msdn page 的备注部分，您会看到一些选择语句。我想生成这些表达式，然后根据要复制到的类是否包含实现该成员的接口(interface)，在父选择中使用它们。我避免使用 linqToObject，因为我只需要在 CopyTo 中定义的属性，但导航属性是接口(interface)，这会破坏 Entity Framework 。这是为了延迟加载目的。 MergeStack 将组合这些表达式并将其返回到树中。我的想法来自 a DaedTech blogpost

Answer 1

Roles 是 IQueryable，因此您需要从 Queryable 扩展类中获取 Select 方法。您还需要从 Enumerable 扩展类中获取 Include。然后，您需要使用 Role 作为通用参数来调用 Select 方法。您需要使用 Expression.Lambda、Expression.Call 和 Expression.Property 构造一个 lambda。