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License: MIT Code of Conduct Build Status Coverage Status

version package
v Qowaiv
v Qowaiv.Data.SqlCient
v Qowaiv.TestTools


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.

(Single) Value Objects

A Value Object is an immutable type that is distinguishable only by the state of its properties. A Single Value Object (SVO) is a Value Object that can be represented by a single scalar/primitive type.

Primitive Obsession

Primitive Obsession is when the code relies too much on primitives. This is seen as bad design, as it leads to error-prone, cluttered code. Using SVO's instead, prevents this.

Struct v.s. Class

All Qowaiv SVO's have been created as struct, not as class. The reason for doing this, is that for primitive like SVO's they should behave similar to the known primitives, like double, int, DateTime, Guid, etcetera.

A consequence of this choice is that SVO's can not be null, and that all default initializations have a meaningful value. That can be Empty, Zero or what suits the SVO best.


Multiple scenarios are supported:

  • Parsing
  • Formatting
  • Validation
  • Serialization (JSON, XML, in-memory)
  • Model binding
  • Domain-specific logic
  • Explicit and implicit casting

Qowaiv types


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

var date = new Date(2017, 06, 11);
var next = date++; // 2017-06-12
var casted = (Date)new DateTime(2017, 06, 11, 06, 15);

Date span

Represents a date span. Opposed to a TimeSpan its duration is (a bit) resilient; Adding one month to a date in January result in adding a different number of days, than adding one month a date in March.

Date spans are particular useful in scenario's for defining (and doing calculations on) month based periods, and ages (mostly in years and days).

var span = new DateSpan(years: 3, months: 2, days: -4);
var age = DateSpan.Age(new Date(2017, 06, 11)); // 2Y+0M+121D on 2019-10-10
var duration = DateSpan.Subtract(new Date(2019, 06, 10), new Date(2017, 06, 11)); // 1Y+11M+30D
var date = new Date(2016, 06, 03).Add(age); // 2018-10-02

Email address

Represents a (single) email address. Supports:

  • Display names (are stripped)
  • Comments (are removed)
  • IP-based domains (normalized and surrounded by brackets)

Furthermore, the email address is normalized as a lowercase string, making it case-insensitive.

var email = EmailAddress.Parse("Test Account <>");
var quoted = EmailAddress.Parse("\"Joe Smith\"");
var ip_based = EmailAddress.Parse("test@[]");

email.ToString(); //
quoted.ToString(); //
ip_based.IsIPBased; // true
ip_based.WithDisplayName("Jimi Hendrix"); // Jimi Hendrix <test@[]>

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.

StreamSize fromMb = StreamSize.FromMegabytes(14.2);
StreamSize parsed = StreamSize.Parse("117.2Kb");

// Short notation
new StreamSize(8900).ToString("s") => 8900b
new StreamSize(238900).ToString("s") => 238.9kb
new StreamSize(238900).ToString(" S") => 238.9 kB
new StreamSize(238900).ToString("0000.00 S") => 0238.90 kB

// Full notation
new StreamSize(8900).ToString("0.0 f") => 8900.0 byte
new StreamSize(238900).ToString("0 f") => 234 kilobyte
new StreamSize(1238900).ToString("0.00 F") => 1.24 Megabyte

// Custom
new StreamSize(8900).ToString("0.0 kb") => 8.9 kb
new StreamSize(238900).ToString("0.0 MB") => 0.2 MB
new StreamSize(1238900).ToString("#,##0.00 Kilobyte") => 1,239.00 Kilobyte
new StreamSize(1238900).ToString("#,##0") => 1,238,900


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].

Month feb = Month.Parse("February");
Month may = Month.May;
Month dec = 12;

feb.ToString("f", new CultureInfo("nl-NL")); // februari
feb.ToString("s"); // Feb
feb.ToString("M"); // 02
feb.ToString("m"); // 2

Month span

Is a subset of the date span, so without the days precision.

// Creation
var ctor = new MonthSpan(years: 5, months: 6); // 69 months.
var months = MonthSpan.FromMonths(13);
var years = MonthSpan.FromYears(3); // 35 months.

// operations
var delta = MonthSpan.Subtract(new Date(2020, 04, 01), new Date(2020, 02, 28)); // 1 month.
var prev = new Date(2017, 06, 11) - MonthSpan.FromMonths(9); // 2016-09-11
var next = new DateTime(2010, 05, 02).Add(MonthSpan.FromMonths(2)); // 2010-07-02


Represents a percentage. It supports parsing from per mile and per ten thousand too. The basic thought is that Percentage.Parse("14%") has the same result as double.Parse("14%"), which is 0.14.

// Creation
Percentage p = 0.0314; // implicit cast: 3.14%
var p = Percentage.Parse("3.14"); //  Parse: 3.14%;
var p = Percentage.Parse("3.14%"); // Parse: 3.14%;
var p = Percentage.Parse("31.4‰"); // Parse: 3.14%;
var p = 3.14.Percent(); // Extension on double: 3.14%;

// Casting
var p = (Percentage)0.500; // 50%
var p = (Percentage)0.33m; // 33%

// Manipulation
var p = 13.2.Percent();
p++; // 14.2%;
var total = 400;
total *= 50.Percent(); // Total = 200;
var value = 50.0;
value += 10.Percent(); // value 55;

var rounded = 17.56.Percent().Round(1); // 17.6%;

var max = Percentage.Max(1.4.Percent(), 1.8.Percent()); // 1.8%;
var min = Percentage.Min(1.7.Percent(), 1.9.Percent()); // 1.7%;

var perMille = 15.5.Percent().ToString("PM"); // 155‰
var perTenThousand = 0.34.Percent().ToString("PT"); // 34‱

Postal code

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

var dutch = PostalCode.Parse("2624DP");
dutch.IsValid(Country.NL); // true
dutch.IsValid(Country.BE); // false

var argentina = PostalCode.Parse("Z1230ABC");
argentina.ToString("AR"); // Z 1230 ABC

Week date

Represents a week based date.


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

Year year = 2017; // implicit;
bool isLeap = year.IsLeapYear;

// behavior similar to double.NaN
Assert.IsFalse(Year.Empty < (Year)2000);
Assert.IsFalse(Year.Empty > (Year)2000);
Assert.IsFalse(Year.Unknown < (Year)2000);
Assert.IsFalse(Year.Unknown > (Year)2000);


A Yes-no is a (bi-)polar that obviously has the values "yes" and "no". It also has an "empty"(unset) and "unknown" value. It maps easily with a boolean, but Supports all kind of formatting (and both empty and unknown) that can not be achieved when modeling a property as bool instead of an YesNo.

// Creation
var yn = YesNo.Parse("ja", new CultureInfo("nl-NL"));
var answer = YesNo.Yes;

if (answer.IsEmptyOrUnknown())
   // Do logic.

if (answer) // Equal to answer.IsYes()
    // Do logic.

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.

Business Identifier Code (BIC)

Represents a BIC as specified in ISO 13616.

var bic = BusinessIdentifierCode.Parse("AEGONL2UXXX");

var business = bic.Business; // "AEGO"
var country = bic.Country; // Country.NL
var location = bic.Location; // "2U"
var branch = bic.Branch; // "XXX"
var length = bic.Length; // 11


Represents a currency based on an ISO 4217 code.

International Bank Account Number (IBAN)

Represents an IBAN as specified in ISO 13616.

var iban = InternationalBankAccountNumber.Parse("nl20ingb0001234567");

iban.Country; // Country.NL
iban.Length; // 18
iban.ToString("F"); // NL20 INGB 0001 2345 67


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

Money money = 125.34 + Currency.EUR;
var sum = (12 + Currency.EUR) + (15 + Currency.USD); // Throws CurrencyMismatchException()
var rounded = money.Round(0); // EUR 125.00

Qowaiv globalization types


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


A CultureInfoScope is a class that allows to specify the current (UI) for the duration/lifetime of specified scope.

using(new CultureInfoScope("es-ES"))
    Console.WriteLine(234.12.ToString()); // 234,12
// or with an extension
using(new CultureInfo("en-ES").Scoped())
    // ...

Qowaiv mathimatical types


A fraction (from Latin fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. It can be written as a/b (a divided by b).

It is worth noticing that the default value of a Fraction is ``Fraction.Zeroand thatNaN` and `Infinity` are not supported.


Fractions can be created in multiple ways:

Fraction fluent = 4.DividedBy(13); // Preferred way

Fraction ctor = new Fraction(4, 13));

Fraction parsed = Fraction.Parse("4/13");
Fraction parsed = Fraction.Parse(""); // single fraction character
Fraction parsed = Fraction.Parse("4²³⁄₄₇"); // Unicode super- and subscript

Fraction fromFloating = Fraction.Create(0.3456786754m);

Fraction casted = (Fraction)34;
Fraction casted = (Fraction)0.3333;


var add = 4.DividedBy(3) +  7.DividedBy(4); // 3 1/12
var subtract = 4.DividedBy(3) - 2.DividedBy(3); // 2/3
var multiply = 3.DividedBy(5) * 2.DividedBy(3); // 6/15
var divide = = 3.DividedBy(5) / 2.DividedBy(3); // 9/10


There are multiple types of formatting supported. Without a fraction bar, the fraction is formatted as a decimal.

var dec = 17.DividedBy(5).ToString("0.##"); // 3,40

If the whole should be formatted as such the by adding the preferred formatting between brackets.

var withWhole = 17.DividedBy(5).ToString("[0]0/0"); // 3 2/5

To specify fraction bar of choice, just define that one in the format:

Fraction bars
name c code
slash / 005C
colon : 003A
division sign ÷ 00F7
fraction slash 2044
division slash 2215
short slash ̷ 0337
long slash ̸ 0338
var customBar = 3.DividedBy(4).ToString("0/÷0"); // 3÷4

Unicode supports super- and subscript, and so does Fraction:

var super = -17.DividedBy(5).ToString("[0]super/sub"); // -3²⁄₅
var super = 5.DividedBy(3).ToString("super/sub"); // ⁵⁄₃

The default format (so if you do not specify anything) is:

var basic = 3.DividedBy(4).ToString("0/0"); // 3/4

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:

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 identifiers

Strongly-typed identifiers

Primitive Obsession is a common issue when dealing with identifiers. It is quite common to provide two or even more identifiers (of different identities) to a method, which can lead to nasty bugs.

To overcome this, strongly-typed identifiers can save the day: a specific type per identifier per identity. Qowaiv's approach is to use an Id<T> where T is a class dealing with the logic/behavior of the underlying values. This gives a lot of flexibility, and requires hardly any code per identifier, as in 99% of the cases, you can fully rely on a base implementation (Guid, long, int, string).

// Definition of the identifiers.
public sealed class ForDocument : Int64IdLogic { }
public sealed class ForPerson : GuidLogic { }
public sealed class ForUser : GuidLogic { }

// Creation
var documentId = (Id<ForDocument>)123457L; // cast
var personId = Id<ForPerson>.Parse("0bb59085-9184-4df9-b9d4-08e1ba65cef8"); // parse
var userId = Id<ForUser>.Create(new Guid("0bb59085-9184-4df9-b9d4-08e1ba65cef8")); // create.
var bytesId = Id<forDocument>.FromBytes(new byte[]{ 17, 0, 0, 0, 0, 0, 0, 0 }); // create from bytes.
var nextId = Id<ForPerson>.Next(); // New ID, a random GUID in this case

var same = personId.Equals(userId); // false, same GUID, different types.

// Export
var docId = (long)documentId; // cast
var perId = personId.ToString(); // "0bb59085-9184-4df9-b9d4-08e1ba65cef8"
var bytId = bytesId.ToByteArray();

// Custom logic
public sealed class ForCustomer : StringIdLogic
    protected override bool IsValid(string str, out string normalized)
        normalized = default;
        if (Regex.IsMatch("$C[1-9][0-9]{4,6}^"))
            normalized = str;
            return true;
        return false;

    public override object Next() => 'C' + Rnd.Next(10_000, 9_999_999).ToString();


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.

var rnd = Uuid.NewUuid();
UuidVersion version = rnd.Version; // UuidVersion.Random = 4

var bytes = Encoding.ASCII.GetBytes("Qowaiv");
var md5 = Uuid.GenerateWithMD5(bytes); //   lmZO_haEOTCwGsCcbIZFFg, UUID Version: 3
var sha1 = Uuid.GenerateWithSHA1(bytes); // 39h-Y1rR51ym_t78x9h0bA, UUID Version: 5


The UUID Comparer can sort both UUID's as GUID's, Furthermore, is support both .NET's default way of sorting as the sorting of SQL Server, or MongoDB.

var uuids = new List<Uuid>();

var uuids = new List<Uuid>();

var guids = new List<Guid>();


As UUID's are commonly used for the clustered key of a database table. For massive database with a lot of inserts (they go hand in hand normally) this can be a performance issue, as by default generated UUID's are not sequential, so the clustered index gets a lot of random inserts.

By using a sequential UUID this problem can be minimized. Obviously, if you can fully rely on the sequential UUID generation by your database of choice, you should consider that, but in most cases you want to generate the ID upfront. In that case Uuid.NewSequential() comes handy:

var uuid = Uuid.NewSequential(UuidComparer.SqlServer);

As databases might (like SQL Server does) order your UUID/GUID's differently that .NET does, this generator does that too. Also keep in mind that this generated ID is not perfectly sequential; first of all because it has a 0.32 nanosecond overlap, but more seriously, as some time may elapse between the generation and the storage in the database. Furthermore, these generated UUID's are not sequential once mixed with the sequential generated UUID's by your database.

Qowaiv statistical types


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

Elo p0 = 1600;
Elo p1 = 1500;
var z = Elo.GetZScore(p0, p1); // 0.64 

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

Decimal round

By default, .NET support rounding of floating points (including decimals). However, for some domains this support is too limited. To overcome this, Qowaiv has the static DecimalRound helper class, containing extension methods for rounding.

‘Negative’ decimals

To round tenfold, hundredfold, etc. precision, a negative amount of decimals can be specified:

var tenfold = 1245.346m.Round(-1); // 1250m
var hundredfold = 1209m.Round(-2); // 1200m

Multiple of

Rounding to a multiple of is supported:

var multipleOf = 123.5m.RoundToMultiple(5m); //   125.0m
var multiple25 = 123.5m.RoundToMultiple(2.5m); // 122.5m

Extra rounding methods

.NET supports rounding to even (Bankers rounding) and away from zero out-of-the-box. Rounding methods like ceiling, floor, and truncate have limited support (0 decimals only), and many others (to odd, half-way up, half-way down, e.o.) are missing. By specifying the DecimalRounding 13 ways are supported.

var toOdd = 23.0455m.Round(3, DecimalRounding.ToOdd); // 23.045m
var towardsZero = 23.5m.Round(DecimalRounding.TowardsZero); // 23m
var randomTie = 23.5m.Round(DecimalRounding.RandomTieBreaking); // 50% 23m, 50% 24,

Model Binding

All SVO's support model binding out of the box. That is to say, when the model binding mechanism works with a TypeConverter. It still may be beneficial to have a custom model binder. Because different solutions might require different custom model binders, and deploying them as NuGet packages would potentially lead to a dependency hell, Qowaiv provides them as code snippets:



Serializing data using JSON is de facto the default. Qowaiv has a (naming) based convention:

public struct Svo
    public static Svo FromJson(string json);

    // When appropriate for the SVO. Example: `Percentage`.
    public static Svo FromJson(double json);

    // When appropriate for the SVO. Example: `Amount`.
    public static Svo FromJson(long json);

    // When appropriate for the SVO. Example: `YesNo`.
    public static Svo FromJson(bool json);

    // In most cases `string` is returned, but there are exceptions:
    // Amount: double ToJson();
    // StreamSize: long ToJson();
    // Year: object ToJson();
    public object /* or string, bool, int, long, double, decimal */ ToJson();


There are two out-of-the-box implementations that that support this convention based contract.

OpenAPI Specification

The OpenAPI Specification (formerly Swagger Specification) is an API description format for REST API's.

To improve usage of your REST API's you should specify the Data Type of your SVO's. To make this as simple as possible, Qowaiv SVO's are decorated with the OpenApiDataTypeAttribute. It specifies the type, format, (regex) pattern, and if the data type is nullable, all when applicable.

  "Date": {
    "description": "Full-date notation as defined by RFC 3339, section 5.6, for example, 2017-06-10.",
    "type": "string",
    "format": "date",
    "nullabe": false
  "DateSpan": {
    "description": "Date span, specified in years, months and days, for example 1Y+10M+16D.",
    "type": "string",
    "format": "date-span",
    "pattern": "[+-]?[0-9]+Y[+-][0-9]+M[+-][0-9]+D",
    "nullabe": false
  "EmailAddress": {
    "description": "Email notation as defined by RFC 5322, for example,",
    "type": "string",
    "format": "email",
    "nullabe": true
  "EmailAddressCollection": {
    "description": "Comma separated list of email addresses defined by RFC 5322.",
    "type": "string",
    "format": "email-collection",
    "nullabe": true
  "Gender": {
    "description": "Gender as specified by ISO/IEC 5218.",
    "type": "string",
    "format": "gender",
    "nullabe": true,
    "enum": [
  "HouseNumber": {
    "description": "House number notation.",
    "type": "string",
    "format": "house-number",
    "nullabe": true
  "LocalDateTime": {
    "description": "Date-time notation as defined by RFC 3339, without time zone information, for example, 2017-06-10 15:00.",
    "type": "string",
    "format": "local-date-time",
    "nullabe": false
  "Month": {
    "description": "Month(-only) notation.",
    "type": "string",
    "format": "month",
    "nullabe": true,
    "enum": [
  "MonthSpan": {
    "description": "Month span, specified in years and months, for example 1Y+10M.",
    "type": "string",
    "format": "month-span",
    "pattern": "[+-]?[0-9]+Y[+-][0-9]+M",
    "nullabe": false
  "Percentage": {
    "description": "Ratio expressed as a fraction of 100 denoted using the percent sign '%', for example 13.76%.",
    "type": "string",
    "format": "percentage",
    "pattern": "-?[0-9]+(\\.[0-9]+)?%",
    "nullabe": false
  "PostalCode": {
    "description": "Postal code notation.",
    "type": "string",
    "format": "postal-code",
    "nullabe": true
  "Uuid": {
    "description": "Universally unique identifier, Base64 encoded, for example lmZO_haEOTCwGsCcbIZFFg.",
    "type": "string",
    "format": "uuid-base64",
    "nullabe": true
  "WeekDate": {
    "description": "Full-date notation as defined by ISO 8601, for example, 1997-W14-6.",
    "type": "string",
    "format": "date-weekbased",
    "nullabe": false
  "Year": {
    "description": "Year(-only) notation.",
    "type": "integer",
    "format": "year",
    "nullabe": true
  "YesNo": {
    "description": "Yes-No notation.",
    "type": "string",
    "format": "yes-no",
    "nullabe": true,
    "enum": [
  "Financial.Amount": {
    "description": "Decimal representation of a currency amount.",
    "type": "number",
    "format": "amount",
    "nullabe": false
  "Financial.BusinessIdentifierCode": {
    "description": "Business Identifier Code, as defined by ISO 9362, for example, DEUTDEFF.",
    "type": "string",
    "format": "bic",
    "nullabe": true
  "Financial.Currency": {
    "description": "Currency notation as defined by ISO 4217, for example, EUR.",
    "type": "string",
    "format": "currency",
    "nullabe": true
  "Financial.InternationalBankAccountNumber": {
    "description": "International Bank Account Number notation as defined by ISO 13616:2007, for example, BE71096123456769.",
    "type": "string",
    "format": "iban",
    "nullabe": true
  "Financial.Money": {
    "description": "Combined currency and amount notation as defined by ISO 4217, for example, EUR 12.47.",
    "type": "string",
    "format": "money",
    "pattern": "[A-Z]{3} -?[0-9]+(\\.[0-9]+)?",
    "nullabe": false
  "Globalization.Country": {
    "description": "Country notation as defined by ISO 3166-1 alpha-2, for example, NL.",
    "type": "string",
    "format": "country",
    "nullabe": true
  "Identifiers.Id<TIdentifier>": {
    "description": "identifier",
    "type": "string/int",
    "nullabe": false
  "IO.StreamSize": {
    "description": "Stream size notation (in byte).",
    "type": "integer",
    "format": "stream-size",
    "nullabe": false
  "Mathematics.Fraction": {
    "description": "Faction",
    "type": "string",
    "format": "faction",
    "pattern": "-?[0-9]+(/[0-9]+)?",
    "nullabe": false
  "Security.Cryptography.CryptographicSeed": {
    "description": "Base64 encoded cryptographic seed.",
    "type": "string",
    "format": "cryptographic-seed",
    "nullabe": true
  "Statistics.Elo": {
    "description": "Elo rating system notation.",
    "type": "number",
    "format": "elo",
    "nullabe": false
  "Web.InternetMediaType": {
    "description": "Media type notation as defined by RFC 6838, for example, text/html.",
    "type": "string",
    "format": "internet-media-type",
    "nullabe": true

OpenApi using Swagger

When using Swagger to implement OpenApi this could be done like below:

/// <summary>Extensions on <see cref="SwaggerGenOptions"/>.</summary>
public static class SwaggerGenOptionsSvoExtensions
	/// <summary>Maps Qowaiv SVO's.</summary>
	public static SwaggerGenOptions MapSingleValueObjects(this SwaggerGenOptions options)
		var attributes = OpenApiDataTypeAttribute.From(typeof(Date).Assembly);
		foreach (var attr in attributes)
			options.MapType(attr.DataType, () => new OpenApiSchema
				Type = attr.Type,
				Format = attr.Format,
				Pattern = attr.Pattern,
				Nullable = attr.Nullable,


.NET supports XML Serialization out-of-the-box. All SVO's implement IXmlSerialization with the same approach:

XmlSchema IXmlSerializable.GetSchema() => null;

void IXmlSerializable.ReadXml(XmlReader reader)
    var s = reader.ReadElementString();
    var val = Parse(s, CultureInfo.InvariantCulture);
    m_Value = val.m_Value;

void IXmlSerializable.WriteXml(XmlWriter writer)
    writer.WriteString(ToString(SerializableFormat, CultureInfo.InvariantCulture));

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 => 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 => 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 clock

The Clock class is an outsider within the Qowaiv library. It is a solution for a problem that is not related to Domain-Driven Design, but to the fact that the behaviour of System.DateTime.UtcNow (and its equivalents) can not be controlled. This can be problematic for writing proper tests that relay on its behaviour.

The default way to tackle this problem is by providing a lightweight service like this one:

public interface IClock
    DateTime UtcNow();

public class Clock : IClock
	public DateTime UtcNow() => DateTime.UtcNow;

However, providing an IClock all the time when there is time related logic is not that elegant at all. The Qowaiv Clock helps to overcome this. In code you just call Clock.UtcNow() or one of its derived methods. In a test you change the behaviour, in most cases just for the scope of your current threat:

public void TestSomething()
    using(Clock.SetTimeForCurrentThread(() => new DateTime(2017, 06, 11))
        // test code.