how to create relationship for polymorphic association

for polymorphic association, how to create relationship.

class Picture < ApplicationRecord
  belongs_to :imageable, polymorphic: true
end
 
class Employee < ApplicationRecord
  has_many :pictures, as: :imageable
end
 
class Product < ApplicationRecord
  has_many :pictures, as: :imageable
end

create_table :pictures do |t|
      t.string  :name
      t.integer :imageable_id
      t.string  :imageable_type
      t.timestamps
end

how to create relationship, so i can query like this

{
     products {
         name
         pictures {
              id
              name
         }
     }
}

thanks !

[0x777]

@dfang @SkaterDad

We don’t natively support polymorphic associations like that of Rails, however you’ll still be able to query like you wanted. The pictures table will be something along these lines:

pictures:
- id: integer 
- name: text 
- imageable_id: integer
- imageable_type: text

You can create views as follows:

create view employee_pictures as select * from pictures where imageable_type = 'employees';
create view product_pictures as select * from pictures where imageable_type = 'products';

Now you can define a manual relationship called pictures on employees and products table using these views. So your queries will now look like this:

{
  employees {
    id
    name
    pictures {
      id
      name
    }
  }
}

Another option is to use through table like @shahidhk suggested, i.e, employee_pictures, product_pictures … etc. If you have such a modelling, Hasura makes it very easy to insert into these tables using relationships, i.e, you can insert a picture and associate it with an employee in a single query. If you have such a modelling, your queries will look like this:

{
  employees {
    id
    name
    pictures {
      picture {
        id
        name
      }
    }
  }
}

So it is up to you to pick a schema design that suits your use case. The GraphQL queries will roughly be the same.

[iam4x]

Hi @0x777

Thank you for the solution, nice workaround with views 👍

But I do have an issue, after creating my new relationship the UI for data schema crash (JS error) with the message “Something went wrong”

If I remove the relationship directly in the database it works again. I’ve traced the JS error to this line: https://github.com/hasura/graphql-engine/blob/c3f4c35141f1187fc2f0f107158c1dff26f34568/console/src/components/Services/Data/TableRelationships/autoRelations.js#L110

Here is my faulty hdb_relationship row:

table_schema	table_name	rel_name	rel_type	rel_def	comment	is_system_defined
public	orders	states	array	{"manual_configuration": {"remote_table": "orders_states", "column_mapping": {"id": "resource_id"}}}	NULL	f

Did I missed something or this is a bug? Thank you.