Change Tracking¶

Enabling Change Tracking¶

Embed document.Tracked alongside document.Base:

import "github.com/oliverandrich/den/document"

type Product struct {
    document.Base
    document.Tracked
    Name  string  `json:"name"  den:"index"`
    Price float64 `json:"price" den:"index"`
}

Den automatically captures a byte-level snapshot of the serialized document after every load or write operation (Save, FindByID, query iteration, Refresh).

Detecting Changes¶

Use den.IsChanged to check if a document has been modified since it was last loaded or saved:

p, _ := den.NewQuery[Product](db, where.Field("name").Eq("Widget")).First(ctx)

changed, _ := den.IsChanged(db, p) // false

p.Price = 29.99

changed, _ = den.IsChanged(db, p) // true

Inspecting Changes¶

Use den.GetChanges to get a field-by-field diff:

p.Price = 29.99

changes, _ := den.GetChanges(db, p)
// map[string]FieldChange{
//     "price": {Before: 19.99, After: 29.99},
// }

Only modified fields appear in the map. If nothing changed, the map is empty.

Reverting Changes¶

Use den.Revert to restore a document to its last-saved state:

p.Price = 29.99
p.Name = "New Name"

den.Revert(db, p)

// p.Price and p.Name are back to their original values
changed, _ = den.IsChanged(db, p) // false

Revert deserializes the stored snapshot back into the struct, undoing all local modifications. The name is deliberately not Rollback to avoid confusion with the backend transaction's Rollback method — Revert is a pure in-memory restore that has nothing to do with transactions.

Warning

den.Revert returns den.ErrNoSnapshot if the document was never loaded from the database (e.g., a freshly constructed struct that has not been inserted or queried).

Combining with Soft Delete¶

Tracked and SoftDelete are independent composable embeds:

type AuditLog struct {
    document.Base
    document.SoftDelete
    document.Tracked
    Action string `json:"action"`
    Detail string `json:"detail"`
}

Tip

See the Documents guide for the full list of composable embeds and example compositions.

How It Works¶

When a document implements the Trackable interface (which document.Tracked satisfies), Den stores a snapshot of the serialized JSON after every database operation:

IsChanged re-encodes the current struct state and compares bytes against the snapshot
GetChanges diffs the two JSON representations to produce a per-field change map
Revert deserializes the stored snapshot back into the struct