@balena/sbvr-types

sbvr-types

This module defines the data types that can be used in the SBVR model specification, as well as the possible relations between them. For each data type, there is a correspondence with a database data type, according to the various database engines that are supported.

The SBVR definition for types can be found at Type.sbvr

"The Rest" can be found at: balena-io-modules/sbvr-types/src/types

How-to

For a new type you should add a module to the types folder. The module should return a single object, which has the following format:

types

A types object, which specifies how the type is declared in various systems. This contains:

• postgres/mysql/websql - These can either be a string (which will have the necessity and index appended to it), or a function (necessity, index), which returns the type as a string.

postgres: 'Serial'
mysql: (necessity, index) ->
	return 'INTEGER' + necessity + index + ' AUTO_INCREMENT'
websql: (necessity, index) ->
	return 'INTEGER' + necessity + index + ' AUTOINCREMENT'

• odata - This is an object that must contain a "name" property, which is a string specifying the name of the OData type. It may also contain a "complexType" property, which is a string that specifies an OData ComplexType

odata:
	name: 'Edm.Int64'

odata:
	name: 'Self.Color'
	complexType: '''
		<ComplexType Name="Color">
			 <Property Name="r" Nullable="false" Type="Edm.Int8"/>\
			 <Property Name="g" Nullable="false" Type="Edm.Int8"/>\
			 <Property Name="b" Nullable="false" Type="Edm.Int8"/>\
			 <Property Name="a" Nullable="false" Type="Edm.Int8"/>\
		</ComplexType>'''

• validate - This is a function (value, required) => Promise that must be provided, and which should validate that incoming data is valid for this type.
  • value is the value that has been received as part of the request.
  • required specifies whether this value is required (true: NOT NULL, false: NULL).
  • Promise should be returned with the resolved value being the valid, processed data, and any rejection being an error message explaining why the data is invalid.

An example of validating a Color type, we accept either a number that specifies the Color, or an object {'r' or 'red', 'g' or 'green', 'b' or 'blue', 'a' or 'alpha'}, and return an integer that represents the Color.

validate: Promise.method (value, required) ->
	if typeof value != 'object'
		processedValue = parseInt(value, 10)
		if Number.isNaN(processedValue)
			throw new Error('is neither an integer or color object: ' + value)
	else
		processedValue = 0
		for own component, componentValue of value
			if Number.isNaN(componentValue) or componentValue > 255
				throw new Error('has invalid component value of ' + componentValue + ' for component ' + component)
			switch component.toLowerCase()
				when 'r', 'red'
					processedValue |= componentValue << 16
				when 'g', 'green'
					processedValue |= componentValue << 8
				when 'b', 'blue'
					processedValue |= componentValue
				when 'a', 'alpha'
					processedValue |= componentValue << 24
				else
					throw new Error('has an unknown component: ' + component)
	return processedValue

• fetchProcessing - This is a function (data) => any that may be specified to process the data after fetching from the database and before sending to the client. If specified this function should return the modified data

fetchProcessing: (data) ->
	return {
		r: (data >> 16) & 0xFF
		g: (data >> 8) & 0xFF
		b: data & 0xFF
		a: (data >> 24) & 0xFF
	}

• nativeProperties - This is an object that may be specified to define "native" properties of the type. If specified it should match the format:

nativeProperties:
	Verb:
		Term: (from) -> ...
		Term2: (from) -> ...
	Verb2:
		Term3: (from) -> ...

The (from) -> ... function should return a chunk of abstract sql that can be used to fetch the property specified by this fact type, the from parameter is abstract sql that will refer to an instance of the term that is of this type.

Text has Length:

	nativeProperties:
		'has':
			'Length': (from) -> ['CharacterLength', from]

For the various properties of Color:

nativeProperties:
	'has':
		'Red Component': (from) -> ['BitwiseAnd', ['BitwiseShiftRight', from, 16], 255]
		'Green Component': (from) -> ['BitwiseAnd', ['BitwiseShiftRight', from, 8], 255]
		'Blue Component': (from) -> ['BitwiseShiftRight', from, 255]
		'Alpha Component': (from) -> ['BitwiseAnd', ['BitwiseShiftRight', from, 24], 255]

• nativeFactTypes - This is an object that may be specified to define "native" fact types of the type. If specified it should match the format:

nativeFactTypes:
	'Term':
		'Verb1': (from, to) -> ...
		'Verb2': (from, to) -> ...
	'Term2':
		'Verb3': (from, to) -> ...

The (from, to) -> ... function should return a chunk of abstract sql that can be used to resolve this fact type.
The from parameter is abstract sql that will refer to an instance of the term that is of this type.
The to parameter is abstract sql that will refer to an instance of the term that is of the type specified by the property name.

Note: The reasoning the ordering of this is SecondTerm -> Verb, rather than Verb -> SecondTerm is that it allows declaring all the links between two terms much easier (as you will see in the examples)

A selection of the the native fact types for Integer (in the actual file much more DRY is practiced):

nativeFactTypes:
	'Integer':
		'is less than': (from, to) -> ['LessThan', from, to]
		'is less than or equal to': (from, to) -> ['LessThanOrEqual', from, to]
	'Real':
		'is less than': (from, to) -> ['LessThan', from, to]
		'is less than or equal to': (from, to) -> ['LessThanOrEqual', from, to]

Note: You only need to specify the verb for the canonical for of the fact type, any synonymous forms will automatically be remapped to the canonical form

Tests

Tests can be found under the test/ folder, to run the whole suite use npm test