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One-to-One

A one-to-one relation means each row on one side has at most one matching row on the other side.

Example​

A user has one profile.

Protocol​

"users": {
  "relations": {
    "profile": {
      "type": "oto",
      "entity": "profiles",
      "prototable": "profiles",
      "fkfield": "id:user_id"
    }
  }
}

Query​

mydb.users{
  id,
  name,
  profile{avatar_url, bio}
}

Response shape​

For oto, the related side is a single object, not an array:

{
  "users": [
    { "id": 1, "name": "Ada", "profile": { "avatar_url": "...", "bio": "..." } }
  ]
}

If no matching row exists, profile is null.

When to use it​

  • A user → profile (1 user, 1 profile)
  • An order → invoice (1 order, 1 invoice)
  • A vehicle → registration

If the related row could legitimately be missing, you'll see null. Plan for it on the frontend.