db-mysql/README.md

# einherjar/db-mysql

[![version](https://img.shields.io/badge/version-v1.1.0-5C4EE5?style=flat-square)](https://code.nochebuena.dev/einherjar/db-mysql)
[![license](https://img.shields.io/badge/license-AGPL--3.0-22863A?style=flat-square)](LICENSE)
[![go](https://img.shields.io/badge/Go-1.26+-00ADD8?style=flat-square&logo=go&logoColor=white)](https://go.dev)
[![health](https://img.shields.io/badge/health-critical-D73A49?style=flat-square)]()

> A warrior's deeds are committed to stone so that what they built survives the builder.

`code.nochebuena.dev/einherjar/db-mysql` is the MySQL/MariaDB database component of the Einherjar framework. It wraps `database/sql` with `go-sql-driver/mysql` behind a lifecycle-aware `Component`, exposes a uniform `Executor` interface for queries and transactions, and provides a `UnitOfWork` that injects the active transaction into context — so repositories never need to know whether they are inside a transaction or not.

---

## Usage

### Setup

```go
import dbmysql "code.nochebuena.dev/einherjar/db-mysql"

db := dbmysql.New(logger, dbmysql.DefaultConfig())
lc.Append(db)   // OnInit opens pool; OnStop closes it
// db is observability.Checkable (PING health check, LevelCritical):
srv.Get("/health", health.NewHandler(logger, db).ServeHTTP)
```

### Querying

```go
// GetExecutor returns the pool when called outside a UnitOfWork.
rows, err := db.GetExecutor(ctx).QueryContext(ctx, "SELECT id, name FROM users WHERE active = ?", true)
defer rows.Close()

var name string
err := db.GetExecutor(ctx).QueryRowContext(ctx, "SELECT name FROM users WHERE id = ?", id).Scan(&name)
```

### Manual transaction

```go
tx, err := db.Begin(ctx)
if err != nil {
    return err
}
defer tx.Rollback()

_, err = tx.ExecContext(ctx, "UPDATE accounts SET balance = balance - ? WHERE id = ?", amount, fromID)
if err != nil {
    return err
}
return tx.Commit()
```

`BeginTx` is available when you need explicit isolation level control:

```go
tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
```

### Unit of work (recommended)

`UnitOfWork` wraps the transaction in context so every call to `GetExecutor` inside `uow.Do` automatically returns the active transaction. Repositories require no changes.

```go
uow := dbmysql.NewUnitOfWork(logger, db)

err := uow.Do(ctx, func(ctx context.Context) error {
    _, err := db.GetExecutor(ctx).ExecContext(ctx, "INSERT INTO orders (...) VALUES (...)", ...)
    return err
})
```

If the function returns an error, the transaction is rolled back. If it returns nil, the transaction is committed.

### Error handling

```go
if err := db.HandleError(someErr); err != nil {
    // MySQL error numbers mapped to xerrors:
    // 1062 ER_DUP_ENTRY      → ErrAlreadyExists
    // 1216 ER_NO_REFERENCED_ROW → ErrPreconditionFailed
    // 1048 ER_BAD_NULL_ERROR → ErrInvalidInput
    // context.Canceled       → ErrCancelled
    // context.DeadlineExceeded → ErrDeadlineExceeded
}
```

`HandleError` is also available as a package-level function: `dbmysql.HandleError(err)`.

---

## Environment variables

| Variable | Required | Default | Description |
|---|---|---|---|
| `EINHERJAR_MYSQL_HOST` | Yes | — | MySQL host |
| `EINHERJAR_MYSQL_PORT` | No | `3306` | Listen port |
| `EINHERJAR_MYSQL_USER` | Yes | — | Database user |
| `EINHERJAR_MYSQL_PASSWORD` | Yes | — | Database password |
| `EINHERJAR_MYSQL_NAME` | Yes | — | Database name |
| `EINHERJAR_MYSQL_MAX_CONNS` | No | `5` | Maximum open connections |
| `EINHERJAR_MYSQL_MIN_CONNS` | No | `2` | Minimum idle connections |
| `EINHERJAR_MYSQL_MAX_CONN_LIFETIME` | No | `1h` | Maximum connection lifetime |
| `EINHERJAR_MYSQL_MAX_CONN_IDLE_TIME` | No | `30m` | Maximum idle time before connection is closed |
| `EINHERJAR_MYSQL_CHARSET` | No | `utf8mb4` | Connection charset |
| `EINHERJAR_MYSQL_LOC` | No | `UTC` | Timezone location |
| `EINHERJAR_MYSQL_PARSE_TIME` | No | `true` | Parse `DATE`/`DATETIME` as `time.Time` |

> **Note:** Set collation at the schema level (DDL), not in the DSN. MariaDB 11.4+ collation names exceed the 1-byte handshake limit in `go-sql-driver`.

---

## Dependency graph

```
contracts  (zero dependencies)
    ↑
  core
    ↑
db-mysql  (contracts, core, go-sql-driver/mysql)
    ↑
  your app
```

---

## Verification

```bash
cd db-mysql/
go build ./...
go vet ./...
go test ./...
gofmt -l .
```

---

> *The hall is built before the warriors arrive.*
> *That is the only guarantee worth making.*