訪問其他模型屬性的自定義驗證方法

Question

我試圖為我的一個實體創建自定義驗證方法，所以我創建了一個繼承自ValidationAttribute的類：

public class OneWheelchairPerTrainAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        // This is where I need to access the other entity property
    }
}

我正在努力的是如何訪問實體上的其他屬性。 這是我的實體：

public class Ticket
{
    public int Id { get; set; }

    [Required]
    public int TimetableId { get; set; }

    [Required]
    public bool Wheelchair { get; set; }

    public virtual Timetable Timetable { get; set; }
}

我正在編寫的驗證批注將應用於Wheelchair屬性，並且需要從我的驗證方法中訪問TimetableId屬性。

Answer 1

您可以使用IsValid重載來傳遞ValidationContext，如下所示：

public class OneWheelchairPerTrainAttribute : ValidationAttribute
{
  public override bool IsValid(object value, ValidationContext context)
  {
    Object instance = context.ObjectInstance;
    Type type = instance.GetType();
    // Here is your timetableId
    Object timeTableId = type.GetProperty("TimetableId ").GetValue(instance, null);

    //Do validation ...
   }
}

Answer 2

驗證多個屬性的另一種（我認為更好）的方法是在class級別進行。

這與您的答案並不完全相同，但是仍然涉及多個屬性驗證。

假設您想讓輪椅成為ID或新對象，但您仍然只想允許一個輪椅：

我的ExactlyOneRequired屬性的示例：

[AttributeUsage(AttributeTargets.Class)]
public class ExactlyOneRequiredAttribute : ValidationAttribute
{
    public string FirstPropertyName { get; set; }
    public string SecondPropertyName { get; set; }

    //Constructor to take in the property names that are supposed to be checked
    public ExactlyOneRequiredAttribute(string firstPropertyName, string secondPropertyName)
    {
        FirstPropertyName = firstPropertyName;
        SecondPropertyName = secondPropertyName;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (value == null) 
           return new ValidationResult("Object must have a value;");

        var neededProperties = validationContext.ObjectType.GetProperties().Where(propertyInfo => propertyInfo.Name == FirstPropertyName || propertyInfo.Name == SecondPropertyName).Take(2).ToArray();
        var value1 = neededProperties[0].GetValue(value);
        var value2 = neededProperties[1].GetValue(value);

        if (value1 == null | value2 == null)
            return ValidationResult.Success;

        return FailedValidationResult();
    }

    public override string FormatErrorMessage(string name) => $"One of the fields: '{FirstPropertyName} or {SecondPropertyName}' is required, it is not allowed to set both.";

    private ValidationResult FailedValidationResult() => new ValidationResult(FormatErrorMessage(FirstPropertyName), new List<string> {FirstPropertyName, SecondPropertyName});
}

用法：

[ExactlyOneRequired(nameof(WheelChairId), nameof(WheelChair))]
public class Train
{
    public int? WheelChairId { get; set; }

    public WheelChair WheelChair { get; set; }
}

當然，您可以期望任意數量的屬性，並根據需要使其具有通用性 。 我的觀點是， 與其對屬性內的屬性名稱進行字符串檢查 ，不如注入屬性名稱是更干凈的方法，