Graphql-Ruby: Creating interfaces that objects can inherit fields from

Question

 module Types::ProgramType include Types::BaseInterface description "Objects which inherit from Program" graphql_name "Program" orphan_types Types::SomeProgramType, Types::AnotherProgramType, Types::ThirdProgramType field :id, ID, null: false field :type, Integer, null: false field :name, String, null: false definition_methods do def self.resolve_type(object, _context) case object.class when SomeProgram then SomeProgramType when AnotherProgram then AnotherProgramType when ThirdProgram then ThirdProgramType else raise "Unknown program type" end end end end module Types class SomeProgramType < Types::BaseObject implements Types:ProgramType field :description, String, null: false end end

I also added queries for SomeProgram types in the query_type file. I was under the impression that adding "implement " to the object types, would allow them to inherit the fields from the interface (per this link: https://graphql-ruby.org/type_definitions/interfaces) and I would be able to query like this:

 query { someProgram(id: 1) { name type description } }

But I am getting errors in graphiql, like "Field 'name' doesn't exist on type 'SomeProgram'". What am I missing?

Update:

My QueryType class:

class QueryType < Types::BaseObject # Add `node(id: ID!) and `nodes(ids: [ID!]!)` include GraphQL::Types::Relay::HasNodeField include GraphQL::Types::Relay::HasNodesField field :some_programs, [SomeProgramType], null: false, description: "all some programs" def some_programs SomeProgram.all end field :some_program, SomeProgramType, null: false do argument :id, ID, required: true end def some_program(id:) SomeProgram.find(id) end end

Ashkinas · Accepted Answer · 2021-10-26 23:38:50Z

1

Can you also share how you expose someProgram in your query type?

You can also debug this by looking into the schema if you are using GraphiQL app. You can see the return type of someProgram which should be type of ProgramType.

You can also update your query to include __typename so maybe start with

query { someProgram(id: 1) { __typename } }

First to see what is the return type and if it's being properly handled in the resolve_type

answered Oct 26, 2021 at 23:38

Ashkinas

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3 Comments

KSC Over a year ago

I added the QueryType above. I tried running your query with typename and now I I'm getting a different error which is much more helpful though still very confusing. "Failed to implement Query.somePrograms, tried:\n\n - Types::QueryType#some_programs, which did not exist\n - NilClass#some_programs, which did not exist\n - Looking up hash key :some_programs or \"some_programs\" on ``, but it wasn't a Hash"

KSC Over a year ago

Messed around with things too much. Fixed it but still can't inherit the fields from the ProgramType interface. Now the the results are: { "data": { "someProgram": { "__typename": "SomeProgram" } } }

Ashkinas Over a year ago

shouldn't the __typename be SomeProgramType? i feel like your resolve_type is not working as expected. I would put a debug message in resolve_type and see where it lands.

KSC · Accepted Answer · 2021-10-28 20:02:56Z

I figured out the issue. I had put implements Types:SomeProgram instead of implements Types::SomeProgram. I was missing a colon.

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