const mixinafBedSheet::ValueEncoder

Implement to convert values to and from Str objects.

ValueEncoders are responsible for encoding Objs to and from Strs so they may be used in URLs and HTML forms.

In general, Fantom objects use toStr() and fromStr() for Str conversion. While this works well for serialisation, it often falls short in the context of a web application. Because in an web application, the object in question is often an entity or DTO from a database, and you need services to create it... which you don't have in a static fromStr() ctor!

Therefore ValueEncoders allow you to use the standard IoC dependency injection and any service of your choice.

Nullablity

Obj values may be null, but they must always be converted to a Str instance since you can't express null as a HTML attribute. Bear this in mind when constructing your ValueEncoder for the empty string is often used to represent null. Example:

const class MyValueEncoder : ValueEncoder {

    override Str toClient(Obj? value) {
        if (value == null) return ""
        ...
    }

    override Obj? toValue(Str clientValue) {
        if (clientValue.isEmpty) return null
        ....
    }
}

The ValueEncoder method signatures allow you to substitute null for some other default value. Example, should you wish, an Int could default to 0 or Date objects could default to today's date.

IoC Configuration

Instances of ValueEncoder should be contributed to the ValueEncoders service and mapped to a Type representing the object it converts.

For example, in your AppModule class:

@Contribute { serviceType=ValueEncoders# }
Void contributeValueEncoders(Configuration config) {
  config[MyEntity#] = config.build(MyEntityEncoder#)
}