在ASP.net核心中创建自定义验证属性

using System.ComponentModel.DataAnnotations;

public class CustomValidationAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        // 在这里编写验证逻辑
        // 如果验证成功，返回ValidationResult.Success
        // 如果验证失败，返回一个包含错误信息的ValidationResult对象
    }
}

using System.ComponentModel.DataAnnotations;

public class StringLengthAttribute : ValidationAttribute
{
    private readonly int _maxLength;

    public StringLengthAttribute(int maxLength)
    {
        _maxLength = maxLength;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (value != null && value is string)
        {
            string stringValue = (string)value;
            if (stringValue.Length > _maxLength)
            {
                return new ValidationResult($"The field {validationContext.DisplayName} must be a string with a maximum length of {_maxLength} characters.");
            }
        }

        return ValidationResult.Success;
    }
}

public class MyModel
{
    [StringLength(10)]
    public string Name { get; set; }
}