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Class Field<ValueT, ContextT>

This class describes a field of some EntityMeta.

Type parameters

Hierarchy

Index

Properties

YieldT

The type of the effects that can be "yielded" from the calculation function

entity

entity: EntityMeta

Reference to the EntityMeta this field belongs to.

identifierCls

identifierCls: FieldIdentifierConstructor

The class of the identifier, that will be used to instantiate a specific identifier from this field.

lazy

lazy: boolean = false

Whether this identifier is lazy (true) or strict (false).

Lazy identifiers are calculated on-demand (when read from graph or used by another identifiers).

Strict identifiers will be calculated on read or during the commit call.

level

level: Levels

Level of the identifier. This attribute is supposed to be defined on the prototype level only.

name

name: any = undefined

The name of the identifiers. Not an id, does not imply uniqueness.

persistent

persistent: boolean = true

Boolean flag, indicating whether this field should be persisted

sync

sync: boolean

Whether this identifier is sync (true) or generator-based (false). Default value is true. This attribute is supposed to be defined on the prototype level only.

Methods

calculation

  • calculation(this: this["CalcContextT"], Y: CalculationContext<this["YieldT"]>): Contexts<ValueT, this["YieldT"]>[ContextT]
  • The calculation function of the identifier. Its returning value has a generic type, that is converted to a specific type, based on the generic attribute ContextT.

    This function will receive a single argument - current calculation context (effects handler).

    When using generators, there's no need to use this handler - one can "yield" the value directly, using the yield construct.

    Compare:

    class Author extends Entity.mix(Base) {
        @field()
        firstName       : string
        @field()
        lastName        : string
        @field()
        fullName        : string
    
        @calculate('fullName')
        * calculateFullName () : ChronoIterator<string> {
            return (yield this.$.firstName) + ' ' + (yield this.$.lastName)
        }
    
        @calculate('fullName')
        calculateFullName (Y) : string {
            return Y(this.$.firstName) + ' ' + Y(this.$.lastName)
        }
    }

    Parameters

    Returns Contexts<ValueT, this["YieldT"]>[ContextT]

equality

  • equality(v1: ValueT, v2: ValueT): boolean
  • The equality check of the identifier. By default is performed with ===.

    Parameters

    • v1: ValueT

      First value

    • v2: ValueT

      Second value

    Returns boolean

initialize

  • initialize<T>(props?: Partial<T>): void
  • This method applies its 1st argument (if any) to the current instance using Object.assign().

    Supposed to be overridden in the subclasses to customize the instance creation process.

    Type parameters

    Parameters

    • Optional props: Partial<T>

    Returns void

Static new

  • new<T>(this: T, props?: Partial<InstanceType<T>>): InstanceType<T>
  • This is a type-safe static constructor method, accepting a single argument, with the object, corresponding to the class properties. It will generate a compilation error, if unknown property is provided.

    For example:

    class MyClass extends Base {
        prop     : string
    }
    
    const instance : MyClass = MyClass.new({ prop : 'prop', wrong : 11 })

    will produce:

    TS2345: Argument of type '{ prop: string; wrong: number; }' is not assignable to parameter of type 'Partial<MyClass>'.
    Object literal may only specify known properties, and 'wrong' does not exist in type 'Partial<MyClass>'

    The only thing this constructor does is create an instance and call the initialize method on it, forwarding the first argument. The customization of instance is supposed to be performed in that method.

    Type parameters

    Parameters

    • this: T
    • Optional props: Partial<InstanceType<T>>

    Returns InstanceType<T>

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