Saving Edits in QGIS Forms

Edit Buffer

When a layer is put into editing mode , all operations performed through the form—such as inserting, updating, or deleting records—are not written directly to the data source.
QGIS uses an edit buffer, an in‑memory structure that:

records every modification made by the user,
allows local undo/redo during the editing session,
isolates changes from the physical dataset until they are explicitly committed.

Warning

The contents of the buffer are temporary: if the editing session ends without saving, the buffer is discarded.

Committing Changes (Save Layer Edits)

Saving occurs when the user clicks Save Layer Edits . At this stage, QGIS performs a commit of the edit buffer to the underlying data source (GeoPackage, Shapefile, PostGIS, etc.).

During the commit:

the buffer is processed and its operations are converted into write actions,
QGIS performs data validation (constraints, required fields, data types, domains, unique values, parent–child relationships),
any validation errors are reported before the commit, preventing inconsistent data from being written.

If validation succeeds, the buffer is cleared and the dataset is updated.

Caution

Errors are displayed in a banner within the map canvas. However, the banner may not always be visible when some panels are in a floating (undocked) state, which can partially cover or obscure the map canvas.

Make sure to check the map canvas if error messages are not immediately visible.

Tip

In case of an error, to understand its cause it is necessary to locate the corresponding message directly within the trigger section of the table associated with the form where the error occurred.

Rolling Back Changes

When editing mode is disabled , QGIS prompts the user to either:

save pending changes, or
discard them.

If the user chooses not to save, QGIS performs a rollback:

the edit buffer is removed,
all unsaved modifications are discarded,
the layer returns to its original on‑disk state.

This process is similar to rolling back a transaction in a relational database.

Handling Parent–Child Relationships

When a layer is part of a relational structure (e.g., a GeoPackage with related tables), forms may include sub‑forms for editing child records.

Technically:

each involved layer maintains its own edit buffer,
modifications to child records are not saved automatically when the parent layer is saved,

Persistence and Disk Writing

At the end of a successful commit:

QGIS writes all changes to the GeoPackage (SQLite) or the target database,
indexes and internal metadata structures are updated,
any database‑level triggers or constraints are executed.

The dataset now reflects the final state of the editing session.