# `Bylaw.Credo.Check.Ecto.NoDataChangesInSchemaMigrations`
[🔗](https://github.com/ryanzidago/bylaw/blob/v0.4.0/lib/bylaw/credo/check/ecto/no_data_changes_in_schema_migrations.ex#L1)

## Basics

> #### This check is disabled by default. {: .neutral}
>
> [Learn how to enable it](`e:credo:config_file.html#checks`) via `.credo.exs`.

This check has a base priority of `high` and works with any version of Elixir.

## Explanation

Keep Ecto migrations focused on database schema changes.

## Examples

Avoid changing rows from a migration:

    def up do
      Repo.update_all(Account, set: [status: :active])
      execute("DELETE FROM expired_sessions")
    end

Prefer a reviewed data-migration script or explicit release task that can
batch, throttle, observe, retry, and resume the work safely:

    mix run priv/repo/data_migrations/backfill_account_statuses.exs

## Why

Ecto migrations normally run while holding the migration lock and inside a
DDL transaction. Row mutations and backfills can make that transaction
unexpectedly long, block application traffic, and couple operational data
work to schema deployment. Separate data migrations can be run at the right
time with the operational safeguards their volume requires.

This check is a best-effort automated guideline, not an airtight boundary.
It reports direct calls to common `Repo` mutation functions and literal SQL
passed to any argument of `execute/1,2` when its first statement, after
leading whitespace and comments, begins with `INSERT`, `UPDATE`, `DELETE`,
or `MERGE`. It intentionally does not guess about helper functions, dynamic
SQL, or application-specific `Repo` wrappers.

If a data change genuinely belongs in a schema migration, disable the check
locally with Credo and document why the exception is safe.

## Options

This check has no check-specific options. Configure it with an empty option
list.

## Usage

Add this check to Credo's `checks:` list in `.credo.exs`:

```elixir
%{
  configs: [
    %{
      name: "default",
      checks: [
        {Bylaw.Credo.Check.Ecto.NoDataChangesInSchemaMigrations, []}
      ]
    }
  ]
}
```

## Check-Specific Parameters

*There are no specific parameters for this check.*

## General Parameters

Like with all checks, [general params](`e:credo:check_params.html`) can be applied.

Parameters can be configured via the [`.credo.exs` config file](`e:credo:config_file.html`).

---

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