Question

我是MVC实体框架核心的新手，我一直在为这个异常而苦苦挣扎，我不知道是什么原因造成的。

我总是得到相同的错误：System.InvalidOperationException：'找不到适合实体类型'Rating'的合适的构造函数。以下参数无法绑定到实体的属性：“日期”，“消息”，“建议”。

在GetAll（）方法中引发了错误：

public class RatingRepository : IRatingRepository {
    private readonly ApplicationDbContext _context;

    public RatingRepository(ApplicationDbContext context) {
        _context = context;
    }

    public void Add(Rating rating) {
        var any = _context.Ratings.Any(r => r.RatingId == rating.RatingId);
        if (!any) {
            _context.Add(rating);
        }

    }

    public IEnumerable<Rating> GetAll() {
        return _context.Ratings.ToList();
    }

    public IEnumerable<Rating> GetFirst(int amount) {
        return GetAll().Take(amount).ToList();
    }

    public void Remove(Rating rating) {
        var any = _context.Ratings.Any(r => r.RatingId == rating.RatingId);
        if (any) {
            _context.Remove(rating);
        }

    }

    public void SaveChanges() {
        _context.SaveChanges();
    }
}

这是存储库实现的接口：

public interface ICodeRepository {
    IEnumerable<string> GetAll();
    void Remove(string code);
    void SaveChanges();
}

这是我的评分等级：

 public class Rating {
    #region Fields
    private double _foodRating;
    private double _atmosphereRating;
    #endregion

    #region Properties
    public int RatingId { get; set; }
    public double FoodRating {
        get {
            return _foodRating;
        }
        private set {
            if (value < 0.0 || value > 5.0) {
                throw new ArgumentException("Give a score between 0 and 5 please.");
            }
            _foodRating = value;
        }
    }
    public double AtmosphereRating {
        get {
            return _atmosphereRating;
        }
        private set {
            if (value < 0.0 || value > 5.0) {
                throw new ArgumentException("Give a score between 0 and 5 please.");
            }
            _atmosphereRating = value;
        }
    }
    public string PersonalMessage { get; set; } //not mandatory
    public string Suggestions { get; set; } //not mandatory 
    #endregion

    #region Constructors
    public Rating(double foodRating, double atmosphereRating, DateTime date, string message = null, string suggestion = null) {
        FoodRating = foodRating;
        AtmosphereRating = atmosphereRating;
        PersonalMessage = message;
        Suggestions = suggestion;
    }
    #endregion

}

这是我将其映射到数据库的方式：

 public class RatingConfiguration : IEntityTypeConfiguration<Rating> {
    public void Configure(EntityTypeBuilder<Rating> builder) {
        builder.ToTable("Rating");

        builder.HasKey(r => r.RatingId);

        builder.Property(r => r.PersonalMessage)
            .HasMaxLength(250)
            .IsRequired(false);

        builder.Property(r => r.Suggestions)
            .HasMaxLength(250)
            .IsRequired(false);
    }
}

在我的ApplicationDb中，我预见了一个DbSet，在OnModelCreating中，我给出了RatingConfiguration。

我需要将其绑定到表单结果，所以这是我的RatingViewModel：

public class RatingViewModel {
    #region Properties
    [Required]
    [DataType(DataType.Text)]
    [Display(Name = "How would you rate the food?")]
    public double FoodRating { get; set; }

    [Required]
    [DataType(DataType.Text)]
    [Display(Name = "How would you rate the atmosphere?")]
    public double AtmosphereRating { get; set; }

    [Display(Name = "Personal message")]
    [DataType(DataType.Text)]
    [StringLength(250, ErrorMessage = "Suggestion is needs to be between 250 and 0 characters")]
    public string PersonalMessage { get; set; }

    [Display(Name = "Any suggestions for next time?")]
    [DataType(DataType.Text)]
    [StringLength(250,ErrorMessage = "Suggestion is needs to be between 250 and 0 characters")]
    public string Suggestions { get; set; }
    #endregion

    #region Constructor
    public RatingViewModel() {

    }

    public RatingViewModel(Rating rating) : this() {
        FoodRating = rating.FoodRating;
        AtmosphereRating = rating.AtmosphereRating;
        PersonalMessage = rating.PersonalMessage;
        Suggestions = rating.Suggestions;
    }
    #endregion
}

现在，如果您能找到引发此异常的原因，请告诉我。如果您还需要我的代码中的其他内容，也请告诉我！

Answer 1

实体框架将加载数据并尝试创建映射的对象。但是，如果指定构造函数，EF将尝试使用它，但它不知道如何处理参数。要解决此问题，只需添加一个空的构造函数。

不知道为什么它不断抛出System.InvalidOperationException

1 个答案: