ASP.NET Core API中User实体迁移报错：无合适构造函数

我在ASP.NET Core API中为User模型编写控制器时，为简化Post方法添加了自定义构造函数，API功能运行正常，但执行add-migration命令时返回如下错误：

No suitable constructor was found for entity type 'User'. The following constructors had parameters that could not be bound to properties of the entity type: cannot bind 'username' in 'User(string username, string email, string password)'.

User模型代码 #

using System.ComponentModel.DataAnnotations;

namespace LivetrailsBackend.Models.DataModels
{
    public class User: BaseEntity
    {
        [Required, StringLength(20)]
        public string UserName { get; set; }

        [Required, EmailAddress]
        public string Email { get; set; }

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

        public ICollection<Trail> Trails { get; set; } = new List<Trail>();
        
        public User(string username, string email, string password)
        {
            UserName = username;
            Email = email;
            Password = password;
        }
    }
}

User控制器Post方法代码 #

[HttpPost]
public async Task<ActionResult<User>> PostUser(string username, string email, string password)
{
    if (_context.Users == null)
    {
        return Problem("Entity set 'LivetrailsDBContext.Users'  is null.");
    }

    if (_context.Users.Any(user => user.Email == email))
    {
        return Problem($"That email is already registered.");
    }

    if (_context.Users.Any(user => user.UserName == username))
    {
        return Problem($"Sorry, the username '{username}' is already taken");
    }

    User user = new User(username, email, password);

  
    _context.Users.Add(user);
    await _context.SaveChangesAsync();

    return CreatedAtAction("GetUser", new { id = user.Id }, user);
}

问题原因与解决方法 #

问题根源是EF Core的构造函数参数绑定规则：EF Core会严格匹配构造函数参数名与实体属性名的大小写，你的构造函数参数是username（小写u），但实体属性是UserName（大写U），名称不匹配导致无法完成绑定。

有两种解决方式：

• 方式一：统一参数与属性名的大小写
  修改构造函数参数名，使其和属性名完全一致：

public User(string userName, string email, string password)
{
    UserName = userName;
    Email = email;
    Password = password;
}

• 方式二：用特性指定参数对应属性
  保留原参数名，通过[property: Name]特性明确参数对应的实体属性（需引入System.ComponentModel.DataAnnotations.Schema命名空间）：

using System.ComponentModel.DataAnnotations.Schema;

public User([property: Name(nameof(UserName))] string username, string email, string password)
{
    UserName = username;
    Email = email;
    Password = password;
}

另外注意：EF Core要求实体必须具备无参构造函数（可以是私有），如果你的BaseEntity没有提供无参构造函数，建议给User类添加一个私有无参构造函数供EF Core内部使用：

private User() { }

内容的提问来源于stack exchange，提问作者dahko37