Default value for fields

[christophweegen]

Hello,

is it possible to assign default values to fields?

For example:

field :my_field, String, null: false, default_value: "My default value"

The guides talk about default value in arguments https://graphql-ruby.org/fields/arguments.html but I didn't find anything about default values for fields.

Thanks!

[rmosolgo]

No, that configuration isn't supported. (Argument default values are defined in the GraphQL spec, eg http://spec.graphql.org/June2018/#sec-Coercing-Field-Arguments.)

Of course, you can implement something like that with

field :my_field, String, null: false

def my_field 
  object.my_field || "Default value" 
end 

I hope that helps!

[christophweegen]

Thanks a lot! This will help! I'm writing a proof of concept for a framework to quickly build schemas in a standardized way. Not sure if my ideas will work out in the end, but either way it's a lot of fun and I learn much about graphql-ruby. If you're interested, I can keep you in the loop if I have something substantial. 🚀

[rmosolgo]

Cool, at a framework level, you could probably implement it with a Field Extension (https://graphql-ruby.org/type_definitions/field_extensions.html), eg

class DefaultValueExtension < GraphQL::Schema::FieldExtension 
  def after_resolve(value:, **_rest)
    if value.nil?
      options[:default_value]
    else 
      value 
    end 
  end 
end 

Like

class Types::BaseField  < GraphQL::Schema::Field 
  def initialize(*args, default_value: nil, **kwargs, &block)
    super(*args, **kwargs, &block)
    if !default_value.nil?
      extension(DefaultValueExtension, default_value: default_value)
    end 
  end 
end 

Then:

field :some_string, String, null: false, default_value: "🎉"

Hope that helps!

[christophweegen]

Hey thanks a lot. I will look into that. Looks exactly like what I had in mind. I guess I will publish a first draft in the following weeks. Looking forward to hear what you think about it. Have a nice weekend!

[ltickett]

That extension solution looks great, but I wonder if there is a reason we might not want to make it out of the box functionality?

Thanks

[rmosolgo]

This was added as fallback_value: back in #4069, although it's not well documented yet -- hopefully that helps!

[ltickett]

Amazing- thank you @rmosolgo

I can see the docs were updated in that PR, so i'm disappointed I missed this!

Is there anywhere else in the docs you feel it makes sense to add a note? I would be happy to raise a PR if it helps.

[rmosolgo]

Yeah, I think it could be called out more in the documentation -- at least a little example following the mention on https://graphql-ruby.org/fields/introduction#field-resolution. Please do add something if you think it'd be helpful!