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c# - 我不断收到错误消息，即我的 .NET 模型需要具有 0 args 或仅可选 args 的构造函数？

问题描述

我正在阅读 .NET REST API 教程，该教程通过 sql server 后端为 .NET 中的命令行命令执行 CRUD。我正在使用邮递员向我的端点发送请求，如果我向我的端点发送一个发布请求，它只带有一个包含 CommandCreateDTO 的所有请求的对象，它会出现此错误： System.ArgumentException: Commander.Models.Command needs to have a constructor with 0 args or only optional args. (Parameter 'type'). 想法？

控制器

//POST api/commands
        [HttpPost]
        public ActionResult<CommandCreateDto> CreateCommand(CommandCreateDto commandCreateDto)
        {
            var commandModel = _mapper.Map<Command>(commandCreateDto);
            _repository.CreateCommand(commandModel);
            _repository.SaveChanges();

        return Ok(commandModel);
    }

CommandReadDto

namespace Commander.Dtos
{
    public class CommandReadDto
    {
    
        public int Id { get; set; }

        public string HowTo { get; set; }

        public string Line { get; set; }

        public CommandReadDto(int Id, string HowTo, string Line)
        {
            this.Id = Id;
            this.HowTo = HowTo;
            this.Line = Line;
        }
        
    }
}

命令创建Dto

namespace Commander.Dtos
{
    public class CommandCreateDto
    {
        public string HowTo { get; set; }

        public string Line { get; set; }

        public string Platform { get; set; }

        public CommandCreateDto(string HowTo, string Line, string Platform)
        {
            this.HowTo = HowTo;
            this.Line = Line;
            this.Platform = Platform;
        }
    }
}

命令模型

using System.ComponentModel.DataAnnotations;

namespace Commander.Models
{
    public class Command
    {
        [Key]
        public int Id { get; set; }

        [Required]
        [MaxLength(250)]
        public string HowTo { get; set; }

        [Required]
        public string Line { get; set; }

        [Required]
        public string Platform { get; set; }

        public Command(int Id, string HowTo, string Line, string Platform)
        {
            this.Id = Id;
            this.HowTo = HowTo;
            this.Line = Line;
            this.Platform = Platform;
        }
    }
}

命令配置文件

using AutoMapper;
using Commander.Dtos;
using Commander.Models;

namespace Commander.Profiles
{
    public class CommandsProfile : Profile
    {
        public CommandsProfile()
        {
            //Source - Target
            CreateMap<Command, CommandReadDto>();
            CreateMap<CommandCreateDto, Command>();
        }
    }
}

标签： c#asp.net.netasp.net-mvcrest

解决方案

Your Automapper CreateMap() is trying to map Command class with CommandReadDto. To do that it is expecting default constructor(Constructor without any parameter) in your Command model.

To solve your problem add new default constructor to your Command.Model class.

using System.ComponentModel.DataAnnotations;

namespace Commander.Models
{
    public class Command
    {
        ...
        
        public Command(){}  //This is missing in your code.

        public Command(int Id, string HowTo, string Line, string Platform)
        {
            this.Id = Id;
            this.HowTo = HowTo;
            this.Line = Line;
            this.Platform = Platform;
        }
    }
}

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