Retention

Audit entries expire automatically. Retention is a property of the repository, configured once at construction time and enforced by a MongoDB TTL index.

How it works

Every Entry[Payload] embeds an EntityWithTTL field, persisted as ttlTime:

type EntityWithTTL struct {
    TTLTime time.Time `json:"ttlTime" bson:"ttlTime"`
}

NewBaseAuditLogRepository creates a TTL index over ttlTime with expireAfterSeconds set from WithRetention (default 180 days). On every Insert, the repository re-anchors TTLTime = time.Now() so the index always measures retention from insert time:

func (r *BaseAuditLogRepository[Payload]) Insert(ctx, entry) error {
    if entry.ID == "" {
        entry.ID = storex.NewEntityID()
    }
    if entry.Timestamp == "" {
        entry.Timestamp = storex.NewDateTime(time.Now())
    }
    entry.TTLTime = time.Now() // always set, ignores caller value
    // ...
}

So callers may leave ID, Timestamp and TTLTime zero — the repository fills them in. (ID and Timestamp are only set when zero; TTLTime is always overwritten.)

Configuring the horizon

repo, err := auditrepo.NewBaseAuditLogRepository[myaudit.AuditLog](l, persistor,
    auditrepo.WithRetention(90*24*time.Hour), // keep entries 90 days
)

The one caveat

A MongoDB TTL index bakes expireAfterSeconds into the index itself. Changing WithRetention only affects the index created for a fresh collection — it does not retroactively change the horizon for an existing index. To change retention for existing data you must drop and recreate the index (standard MongoDB TTL behaviour).

TTL is storage-only

TTLTime never reaches the read-side wire surface. The public conversion (entryFromStore) drops the embedded EntityWithTTL deliberately — retention is an operational concern, not part of the audit record consumers see.