Possible to apply defaults on validation?

[Fannon]

Hi!

Is it possible to have a mode where the validation can actively apply the default values of the schema to the properties of the validated object? This would be a great feature, since then I don't have handle the objects with gloves and test for property existence first.

Best, Simon

[mauritsl]

+1 Default values are very useful. I need it as well for a project of mine.

However, applying default values is not strictly a part of validation. Thus it gives the library 2 core functions; validation and applying default values. For that reason, a separate project would work fine too (this is done for JSV, see https://github.com/fhellwig/jsvutil).

[geraintluff]

Do you mean adding any default values there are, or adding default values for properties that are required?

[mauritsl]

In fact is implicitly changes the property to required, or at least it results in the property always having a value. Does require means that it should have that property before validation or after validation?

The JSON Schema standard has very little info about using "default": http://json-schema.org/latest/json-schema-validation.html#anchor101

Schema example:

{
  "type": "object",
  "properties": {
    "title": {"type": "string"},
    "published": {"type": "boolean", "default": true},
  }
}

Input:

{"title": "test"}

should become:

{"title": "test", "published": true}

It doesn't make sense to add "required" in this schema, so we should probably ignore "required" when a default value is given.

[Fannon]

Yes, exactly!

The use case would be to use JSON Schema for describing internal datastructures of a program. For example if a function expects a parameter to be an object, holding options.

Required is sort of ambigious in that case. But I guess it can safely be ignored. It doesn't much sense to require something but offer a default for it at the same time?

[adius]

+1

[geraintluff]

Have you seen tv4-coerce?

I started it a while ago, with the intention that it could provide "coercive validation" (an idea that would include e.g. inserting missing properties), but it didn't get much attention.