Linq.Select()中的嵌套表达式方法调用 [英] Nested Expression method call in Linq.Select()

问题描述

在每次命中数据库后，我都使用.Select(i=> new T{...})将我的实体对象转换为DTO对象.这是一些示例实体和DTOS

I use .Select(i=> new T{...}) after every db hit manually to convert my entity objects into DTO object. Here are some sample entities and 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；

UserEx entity;

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

UserEx DTO;

UserEx DTO;

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

我的转化表达方法；

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

And my current usage for UserDTO;

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

对于UserExDTO；

for UserExDTO;

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

很抱歉为您介绍过多，现在这是我的问题； 我需要分组

Apologize for long introduction, now here is my question ; I need to group

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

由于单点关注.所以我想要这样的东西；

due to single point of concerns. So I want something like this;

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()
    };
}

有什么方法可以做到，还是应该写下每个与相似需求无关的表达式?

Is there any way to do that or should I write down every expression individual and nonrelated to similar needs?

推荐答案

我已经解决了我的问题，而不仅仅是NeinLinq.这是我的解决方案； 您需要先删除嵌套的声明.

I've solved my issue and beyond only with NeinLinq. Here is my solution; You need to remove nested declarations first.

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；

Then use To method of NeinLinq to define the translation;

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());
    }

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