Ploch.Common.DataAnnotations

Custom System.ComponentModel.DataAnnotations validation attributes for date and time model properties.

Overview

Ploch.Common.DataAnnotations is a small focused library that extends the standard .NET data annotation system with validation attributes not available in the BCL. It targets netstandard2.0 and net6.0.

The library currently provides one attribute: RequiredNotDefaultDateAttribute, which validates that a date or date-time property has been explicitly set and is not the language default value. This is distinct from the standard [Required] attribute, which only tests for null — a DateTime property with default value (DateTime.MinValue, i.e. 0001-01-01) is non-null and would pass [Required], but would fail [RequiredNotDefaultDate].

Installation

dotnet add package Ploch.Common.DataAnnotations

Key Types

Type	Description
RequiredNotDefaultDateAttribute	Validates that a DateTime, DateTimeOffset, or DateOnly (net6.0+) property is not null and not equal to its default value. Returns invalid for any other type, including TimeOnly.

Usage Examples

Model validation

using System.ComponentModel.DataAnnotations;
using Ploch.Common.DataAnnotations;

public class CreateEventRequest
{
    [Required]
    public string Title { get; set; } = string.Empty;

    // Ensures the date was explicitly provided and is not 0001-01-01
    [RequiredNotDefaultDate]
    public DateTime StartDate { get; set; }

    // Works with DateTimeOffset
    [RequiredNotDefaultDate]
    public DateTimeOffset PublishedAt { get; set; }

    // Works with DateOnly on .NET 6+
    [RequiredNotDefaultDate]
    public DateOnly DueDate { get; set; }
}

Manual validation

var attribute = new RequiredNotDefaultDateAttribute();

attribute.IsValid(DateTime.Now);         // true
attribute.IsValid(default(DateTime));    // false  (0001-01-01 00:00:00)
attribute.IsValid(null);                 // false
attribute.IsValid(DateTimeOffset.Now);   // true
attribute.IsValid(default(DateTimeOffset)); // false

Default error message

The default message uses the standard {0} placeholder for the display name of the property:

The StartDate field is required and must not be the default date or date time value.

You can override the message through the standard ErrorMessage property:

[RequiredNotDefaultDate(ErrorMessage = "Please provide a valid start date.")]
public DateTime StartDate { get; set; }

Supported Types

Type	Supported	Notes
DateTime	Yes	All target frameworks
DateTimeOffset	Yes	All target frameworks
DateOnly	Yes	net6.0 and later only
TimeOnly	No	Returns invalid for TimeOnly values
Other types	No	Returns invalid

Related Libraries

• Ploch.Common — Core library with Guard argument checking that complements model-level validation with code-level precondition enforcement.