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What does Nullable mean in Hasura? Researching a definition

Nullable, what's the definition? This answer is based on my own research and reading articles and docs.

Nullable GraphQL field on Hasura definition (specifically in the context of GraphQL):

  • Nullable: Optional (if data is provided, it must be the correct type, no data or null is also an option)
  • Not-nullable: Required (data of the correct type must be provided)

Hasura seems great, but sometimes the docs are a little unclear to me as a beginner. One area of that is the nullable tickbox while creating new tables. I can't find a clear definition of Nullable in the UI, or the docs (just references that seem to assume you already know what it is), and googling 'Nullable' leads to C code references. So this is my thought process and googling digging for an answer I can directly understand.Definitely no guarantees I came to the correct answer, but I know which buttons work in Hasura now!

Hasura GraphQL Nulls Cheatsheet has the following code snippet:


interface User {
  name?: string // opting into optional name
  name: string | null // opting into nullable name


type User {
  name: String! // opting into non-nullable name

I know from another project (working with Prisma and Postgres) that a Prisma model with ? is optional. So this code snippet to me appears to be saying, User.name? is optional, and GQL User.name has opted into being non-nullable. As in, it's opted into being non-optional, AKA required.

Above, this is explained via "But in GraphQL, all types are nullable by default, and you opt into non-nullability."

Which helps me understand nullable isn't directly the same as optional, but doesn't say what it is.

The same article later offers a cheatsheet, found at Direct link to GraphQL Nulls Cheatsheet Image.

Here's that image, full credit to Hasura Hasura GraphQL Nulls Cheatsheet

This offers the following info about Nulls in Graphql:

Nullable inputs are always optional

Non-null inputs are always required

A secondary source Hasura Custom GraphQL Types docs offers this snippet

type UserInfo {
  accessToken: String!
  userId: Int!

This is an object type called UserInfo that has two fields: accessToken: This field is of type String! (non-nullable String) userId: This field is of type Int! (non-nullable Int)

After some testing with Hasura, I've discovered the following:

  • A table column that is not ticked as nullable (so is not-nullable) is required to submit a mutation. When data is passed in to the not ticked column, the mutation runs fine.
  • When the same column has nullable ticked on (making the column nullable), the same mutation can be successfully run, saving data, with an empty field. The field also runs when null is passed.

So to recap where I'm at so far:

  • Not Nullable = column must have the expected type data

  • Nullable = column can be empty or set to null, or the expected type

  • Nullable in this context works like this: A graphql entry can be either empty, have the expected data, or set to null

  • Not-nullable enforces the expected data is passed

So extrapolating, a definition of nullable (specifically in the context of GraphQL on Hasura) I can understand is:

  • Nullable: Optional, correct type required, no data or null is fine
  • Not-nullable: Required, correct type must be passed

15th Aug: I had the bright idea to check YouTube for Hasura Data Modelling guides, and found a great video - Hasura YouTube Channel - Data Modelling Video, Timestamped to Nullable reference. In the video nullable is explained as "which means that there's going to be something that I could leave empty inside of my database, and I'm not going to run into any issues with that." This matches nicely with my own research, which is great!