# `MishkaCmsCore.Runtime.Resources.Validations.GlobalRowIsMasterOnly`
[🔗](https://github.com/mishka-group/mishka_cms_core/blob/v0.0.1/lib/mishka_cms_core/runtime/resources/__validations/global_row_is_master_only.ex#L5)

Stops a tenant changing a row that belongs to no site.

## What it is for

On a `global? true` resource a tenant can READ the global rows — that is what `global?` is for.
Nothing in Ash stops them WRITING to one, and for a review note that mattered: a note on a shared
component is visible to every site using it, so a tenant closing one would be answering on
everybody's behalf about a component they cannot even edit.

Reading is untouched, and so is creating: a tenant's own note is stamped with their site by the
tenant create action, so it is never global in the first place. This guards only the actions that
change a row that already exists.

## Usage

    update :resolve do
      validate GlobalRowIsMasterOnly
    end

It reads the row's CURRENT `site_id` — `Ash.Changeset.get_data/2`, not `get_attribute/2` — because
the question is what the row is, not what the changeset would like it to become.

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*Consult [api-reference.md](api-reference.md) for complete listing*