GraphQL JSON data type

Questions / Help
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1

I have json type field on Postgres and trying to create object type in GraphQL but compiler issuing error:

== Compilation error in file lib/community_web/schema.ex ==
** (Absinthe.Schema.Error) Invalid schema:
/Users/kishore/CodeLearning/Elixir/community/lib/community_web/schema.ex:21: Values :json is not defined in your schema.

Types must exist if referenced.

lib/absinthe/schema.ex:271: Absinthe.Schema.__after_compile__/2
(stdlib) lists.erl:1263: :lists.foldl/3
(stdlib) erl_eval.erl:680: :erl_eval.do_apply/6
(elixir) lib/kernel/parallel_compiler.ex:206: anonymous fn/4 in Kernel.ParallelCompiler.spawn_workers/6

Here is object definition:
object :field_values do
field :id, non_null(:id)
field :name, :string
field :description, :string
field :values, :json
end

Do I need to create custom object type? but as per the documentation http://graphql-elixir.org/docs/basic-types/ :json is data type.

Please help.

2

The json db type may have an array or a map with unstructured keys. Unstructured data is strictly forbidden in GraphQL, so you’ll need to work around it. You have two primary options:

  1. If you are storing semi-structures data in the field (like a list of strings, of a map with a few possible keys), then make an object with those fields.
  2. If you have arbitrary data in there then you can send it as a string and have the client decode it.

In our primary GraphQL API we use both of these techniques.

One caveat, if you do go with option 2: enforce the size of the arbitrary data that can be stored. For example, if you have a meta field with client provided values you should restrict the serialized JSON to a fixed length. We do this and limit data to 1024 characters.

1 Like
3

Basic Types - GraphQL Elixir is the documentation for graphql | Hex but it looks like you are using absinthe | Hex

In Absinthe :json is not built-in and you need to add it to your project manually. Generally speaking you want to be cautious on over-relying on untyped JSON in GraphQL, but a JSON field in Postgres sounds like a good use case to me :+1:

Here are the instructions for adding a custom JSON type in Absinthe:

2 Likes
4

Thank you for info and recommendations.

5

Thank you and seems this is the only way to crate custom json types.

6

I don’t know GraphQL well enough to try to help with the immediate problem, but there is a deeper conceptual problem going on here. JSON is not a data type. It is an encoding format. Even though that is the “field type” in the database, you conceptually have some sort of business domain type you are storing that way. That business domain type is what you should expose via GraphQL.

Exposing your field as a “json type” is basically working against the GraphQL goal of specifying your types explicitly. If you are not very careful, this will become a maintenance problem over time.

1 Like
7

Thanks much for advise, got your point.