# Sequences

Bind a column to a PostgreSQL sequence with [AutoIncrement] in Socigy.OpenSource.DB v0.3.2.

## `[AutoIncrement]`

Marks a property as a sequence-backed column. The migration tool creates a named PostgreSQL sequence and sets `nextval('...')` as the column default.

```csharp
[Table("log_entries")]
public partial class LogEntry
{
    [PrimaryKey]
    public Guid Id { get; set; }

    [AutoIncrement]
    public int Seq { get; set; }

    public string Message { get; set; }
}
```

## Sequence naming convention

The generated sequence name follows the pattern `{table}_{column}_seq`:

| Table | Column | Sequence name |
|-------|--------|---------------|
| `log_entries` | `seq` | `log_entries_seq_seq` |
| `orders` | `order_number` | `orders_order_number_seq` |

Pass a name to the attribute to override the convention: `[AutoIncrement("custom_seq_name")]`.

## Generated DDL

```sql
CREATE SEQUENCE IF NOT EXISTS "log_entries_seq_seq" AS INTEGER;

CREATE TABLE "log_entries" (
    "id"      UUID    NOT NULL,
    "seq"     INTEGER NOT NULL DEFAULT nextval('log_entries_seq_seq'),
    "message" TEXT    NOT NULL,
    PRIMARY KEY ("id")
);
```

## Usage

Because `[AutoIncrement]` is effectively a database-side default, use `ExcludeAutoFields()` to let PostgreSQL assign the sequence value:

```csharp
var entry = new LogEntry
{
    Id      = Guid.NewGuid(),
    Message = "Application started",
};

await entry.Insert()
    .WithConnection(conn)
    .ExcludeAutoFields()
    .ExecuteAsync();
```

After the insert, `entry.Seq` reflects the value PostgreSQL assigned only if you re-fetch the row or use `WithValuePropagation()`. The plain insert does not return the generated value inline.

## Notes

- `[AutoIncrement]` does **not** imply `[PrimaryKey]`. Primary key and sequence are orthogonal: you can keep a UUID primary key alongside a sequence counter column, as shown above.
- Sequences are `INTEGER` by default. For a `BIGINT` sequence, declare the property as `long` (the sequence type follows the property type).
- `[AutoIncrement]` is valid only on `short`, `int`, or `long` properties. Any other type is reported as error [`SCGDB001`](/database/0.3.2/advanced/generator-diagnostics).