Qowaiv is a Single Value Object library
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Domain-driven design bottom up

Qowaiv is a (Single) Value Object library. It aims to model reusable (Single) Value Objects that can be used a wide variety of modeling scenarios, both inside and outside a Domain-driven context.

Supported scenarios include parsing, formatting, validation, (de)serialization, and domain specific logic.

Single Value Object

A Value Object that can be represented by a single scalar.

Technical requirements

Because we use .NET standard to support both .NET 4.5 (and higher) as .NET Standard (2.0) the Visual Studio solution file requires VS2017.3 or higher. Visual Studio can be downloaded here: visualstudio.com/downloads.

Qowaiv types


Represents a date, so without hours (minutes, seconds, milliseconds).


Represents an Elo (rating), a method for calculating the relative skill levels of players in competitor-versus-competitor games.

Email address

Represents a (single) email address, including IPv4 domains.

Email address collection

Represents a collection of unique email addresses, excluding the empty and unknown email address.

Stream size

Represents the size of a file or stream.


Represents a gender based on an ISO 5218 code.

House number

Represents a house number in the range [1-999999999].

Local Date Time

Explicitly marked local date time. It allows the clear distinction between local and UTC-based date times.


Represents a month in the range [1-12].


Represents a percentage/per mile/per ten thousand.

Postal code

Represents a postal code. It supports validation for all countries.


The UUID (Universally unique identifier) aka GUID (Globally unique identifier) is an extension on the System.Guid. It is by default represented by a 22 length string, instead of a 32 length string.

Week date

Represents a week based date.


Represents a year in the range [1-9999].

Qowaiv cryptographic types


A seed, representing random data to encrypt and decrypt data.

Qowaiv financial types


Represents money without the notion of the actual currency.

Bank Identifier Code (BIC)

Represents a BIC as specified in ISO 13616.


Represents a currency based on an ISO 4217 code.

International Bank Account Number (IBAN)

Represents an IBAN as specified in ISO 13616.


Represents the amount and the currency. Technically this is not SVO. However it acts identically as a SVO.

Qowaiv globalization types


Represents a country based on an ISO 3166-1 code (or 3166-3 if the country does not longer exists).

Qowaiv SQL types


Represents a (MS SQL) time-stamp is a data type that exposes automatically generated binary numbers, which are guaranteed to be unique within a database. time-stamp is used typically as a mechanism for version-stamping table rows. The storage size is 8 bytes. See: https://technet.microsoft.com/en-us/library/aa260631%28v=sql.80%29.aspx

Qowaiv Data

SVO Parameter factory class

To create a (SQL) parameter with a SVO as value, use the SvoParamater factory class. It will return SQL parameter with a converted database proof value.

Qowaiv web types

Internet media type

Represents an Internet media type (also known as MIME-type and content type).

Qowaiv complex types

Wildcard pattern

Represents a pattern to match strings, using wildcard characters ? and *. It also support the use of SQL wildcard characters _ and %.

Qowaiv helpers


Guard parameters, for centralizing and simplifying the argument checking.

Qowaiv SVO options


To support hashing (object.GetHashCode()) the hash code should always return the same value, for the same object. As SVO's are equal by value, the hash is calculated based on the underlying value.

Due to IXmlSerialization support, however, the underlying value is not read-only, because this interface first create default instance and then sets the value. Only if somebody intentionally misuses the IXmlSerialization interface, can change a value during the lifetime of a SVO.


#pragma warning disable S2328
// "GetHashCode" should not reference mutable fields
// See README.md => Hashing

is fine.


SVO's support sorting. So, LINQ expressions like OrderBy() and OrderByDescending() work out of the box, just like Array.Sort(), and List.Sort(). However, the comparison operators (<, >, <=, >=) do only make sense for a subset of those, and are not implemented on all.


#pragma warning disable S1210
// "Equals" and the comparison operators should be overridden when implementing "IComparable"
// See README.md => Sortable

is fine for types that are sortable via IComparable (in most cases).

Debugger display

During debugging sessions, by default, the IDE shows the result of ToString() on a watch. Although Tostring() is overridden for all Qowaiv Single Value Objects, for debugging a special debugger display is provided too, using a debugger display attribute.

The debugger display attribute refers to (private) property with the name "DebuggerDisplay", which represents the Single Value Object as string. If supported, formatted, and in case of a Empty or Unknown value with a notification of that too. The outcome of the DebuggerDisplay is tested in the UnitTests.

Because the rendering of debugger display is handled based on the development environment, and methods as debugger display are not supported by VB.NET, the debugger display attribute refers to a property instead.

Qowaiv Formatting

Formatting is an important part of the functionality in Qowaiv. All SVO's implement IFormattable, and have custom formatting. For details, see the different remarks at the ToString(string, IFormatProvider).

Formatting arguments

The formatting arguments object, is a container object (struct) of the format and the format provider, the two arguments required for the System.Iformatable ToString() method.

Formatting arguments collection

This collection of formatting arguments stores them based on a type to apply on. On top of that, it has a Format() method, that is an extended implementation of string.Format(). The difference between these two methods is, that - when no custom format is supplied at the format string - string.Format() the default formatting of the object is used, where FormattingArgumentsCollection.Format() uses the default specified at the formatting collection of a type (if available).


========= Because there are scenario's where you want to set typical values as a country or a currency for the context of the current thread (like the culture info) there is a possibility to add these to the Qowaiv.Threading.ThreadDomain.

These values can be configured (in the application settings) or can be created with a creator function that can be registered. If not specified otherwise the current country will be created (if possible) based on the current culture.

Qowaiv Component Model


We're extending the DataAnnotations from Microsoft with some more attributes:

  • [Mandatory] Here the difference with Microsoft's [Required] attribute is that it works for value types as well, it will be invalid if the default value is used.
  • [AllowedValues] and
  • [ForbiddenValues] make it easy to validate string values, or objects/value types that have a string representation.
  • [Any] Tells that a collection should have at least one item.

Result model

Also we propose a Result model that includes the validation messages, and Result which can contain both an object and validation messages. This can be a helpful return type for methods that need to return objects but first have to validate them.

Result<DataType> result = Result.For(data);
Result<DataType> resultWithMessages = Result.For(data, messages);

ValidationMessages with severity

The difference with Microsoft's default ValidationResult and ValidationMessages is that in this PR we support a severity: info, warning, or error.

Those messages can be created via factory methods:

var none = ValidationMessage.None;
var info = ValidationMessage.Info(message, args);
var warn = ValidationMessage.Warning(message, args);
var error = ValidationMessage.Error(message, args);

Or contained by a Result or Result<T>:

Result result = Result.WithMessage(messages);
Result<DataType> result = Result.WithMessage<DataType>(messages);