c# - Linq.Select() 中的嵌套表达式方法调用

Question

我在每次数据库命中后手动使用 .Select(i=> new T{...}) 将我的实体对象转换为 DTO 对象。以下是一些示例实体和 DTOS

用户实体；

public partial class User
{
    public int Id { get; set; }
    public string Username { get; set; }
    public virtual UserEx UserEx { get; set; }
}

用户DTO；

public class UserDTO
{
    public int Id { get; set; }
    public string Username { get; set; }
}

UserEx实体；

public class UserEx
{
    public int UserId { get; set; }
    public string MyProperty1 { get; set; }
    public virtual User User { get; set; }
}

UserEx DTO；

public class UserExDTO
{
    public int MyProperty1 { get; set; }
    public UserDTO UserModel { get; set; }
}

我的转化表达方式；

public static class ConversionExpression
{
    public static Expression<Func<UserEx, UserExDTO>> GetUserExDTOConversionExpression()
    {
        return userEx => new UserExDTO
        {
            MyProperty1 = userEx.MyProperty1,
            UserModel = new UserDTO
            {
                Id = userEx.User.Id,
                Username = userEx.User.Username
            }
        };
    }

    public static Expression<Func<User, UserDTO>> GetUserDTOConversionExpression()
    {
        return user => new UserDTO
        {
            Id = user.Id,
            Username = user.Username
        };
    }
}

以及我目前对 UserDTO 的使用情况；

myContext.Users
    .Select(ConversionExpression.GetUserDTOConversionExpression())
    .ToList();

对于 UserExDTO；

myContext.UserExes
    .Select(ConversionExpression.GetUserExDTOConversionExpression())
    .ToList();

为冗长的介绍道歉，现在这是我的问题；我要分组

new UserDTO
{
    Id = userEx.User.Id,
    Username = userEx.User.Username
}

由于单点问题。所以我想要这样的东西；

public static Expression<Func<UserEx, UserExDTO>> GetUserExDTOConversionExpression()
{
    return userEx => new UserExDTO
    {
        MyProperty1 = userEx.MyProperty1,
        //this line does not behave like the other one 
        UserModel = userEx.User.GetUserDTOConversionExpression()
    };
}

有什么办法可以做到这一点，还是我应该写下与类似需求无关的每个表达方式？

Answer 1

我只用 NeinLinq 就解决了我的问题，而且不止于此。这是我的解决方案；您需要先删除嵌套声明。

public static Expression<Func<UserEx, UserExDTO>> GetUserExDTOConversionExpression()
{
    return userEx => new UserExDTO
    {
        MyProperty1 = userEx.MyProperty1
        //We removed other model declaration here.
    };
}

然后使用NeinLinq的To方法定义翻译；

public static Expression<Func<UserEx, UserExDTO>> GetUserExDtOCompbinedExpression()
    {
    //Translate() and To() methods do all the job
    return GetUserDTOConversionExpression().Translate()
       .To(userEx => userEx.User, userExDTO => userExDTO.UserModel, GetUserExDTOConversionExpression());
    }