document behaviour when id _eq: undefined or null

[pronevich]

Everything worked well, but then on the client-side happened issue when selected for deletion item id has become undefined and as result, all items in the table was deleted:

{
  variables: { where: { id: { _eq: undefined } } },
}

[0x777]

The reason why this happens is because:

where: { id: { _eq: null } }

reduces to

where: { id: {} }

which further reduces to

where: {}

and {} translates to true. {} translating to true is something that we cannot change now as it breaks a lot of already existing queries. @shahidhk opened this a while ago. I've added my thoughts there.

For now I suggest you to write the delete mutation as follows:

mutation delete_article($article_id: Int!) {
  delete_article(where: {id: {_eq: $article_id}}) {
    affected_rows
  }
}

and the variables will then be:

{
  "article_id": 1
}

Since $article_id is defined to be of type Int!, a null value will never be accepted.

[m0ngr31]

Happened to me twice recently. Wasn't a good situation. Would be good to have this explicitly documented.

[leimantas]

I don't use:
where: { id: { _eq: null } }

Safer:
where: {id: {_in: [ ]}}

So if somehow ID becomes undefined - mutation does not affect any rows.

[pronevich]

@leimantas but this is just a temporary escape hatch, in any time new team member that doesn't know all hasura quirks could catch this issue.

[pnappa]

The reason why this happens is because:

where: { id: { _eq: null } }

reduces to

where: { id: {} }

I think this could be fixed by preventing nullable types from being compared with some operators (e.g. {_eq: X } requires X to be some type Y!). The reduction from { _eq: null } to {} is unintuitive to those unfamiliar with ternary-valued logic in SQL, especially when the column being compared is non-nullable. My 2 cents is that exposing this as a type error is a far more elegant solution to now.

[marionschleifer]

This has been documented here: https://hasura.io/docs/1.0/graphql/manual/queries/query-filters.html#evaluation-of-null-values-in-comparision-expressions.

[pronevich]

@marionschleifer but the issue still here - one day some broken code could return null / undefined to graphql expression and we will be in troubles

[marionschleifer]

@pronevich we are tracking this issue here .