1. 在模型类中添加数据注解来验证EndDate大于StartDate。

示例代码：

public class MyModel { [Required] public DateTime StartDate { get; set; }

[Required]
[GreaterThan(nameof(StartDate), ErrorMessage = "EndDate must be greater than StartDate.")]
public DateTime EndDate { get; set; }

}

2. 自定义数据注解来验证EndDate大于StartDate。

示例代码：

public class GreaterThanAttribute : ValidationAttribute { private readonly string _comparisonProperty;

public GreaterThanAttribute(string comparisonProperty)
{
    _comparisonProperty = comparisonProperty;
}

protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
    var property = validationContext.ObjectType.GetProperty(_comparisonProperty);

    if (property == null)
    {
        return new ValidationResult($"Property {_comparisonProperty} not found.");
    }

    var comparisonValue = property.GetValue(validationContext.ObjectInstance, null);

    if (comparisonValue != null && value != null && (DateTime)value <= (DateTime)comparisonValue)
    {
        return new ValidationResult(ErrorMessage);
    }

    return ValidationResult.Success;
}

}

在模型类中使用自定义数据注解。

示例代码：

public class MyModel { [Required] public DateTime StartDate { get; set; }

[Required]
[GreaterThan(nameof(StartDate), ErrorMessage = "EndDate must be greater than StartDate.")]
public DateTime EndDate { get; set; }

}

然后，只需使用ModelState.IsValid来验证模型是否有效。