Edit Form shows and saves raw default-values from geopackage, spatialite or sqlite

[andreglauser]

Describe the bug

QGIS shows default values from sqlite tables as string in the edit-form in case of creating a new row. After save, the raw default values are stored in the table.

QGIS-form with new feature and 'wrong' default-values. Feature from sql-insert with id 1 in background.

QGIS-table after save_ shown with pointless default-values.

How to Reproduce

1. Create table in sqlite, spatialite or geopackage or use provided project default_field_value.zip

-- create the test-table
CREATE TABLE my_table (
    id integer primary key autoincrement,
    comment text,
    created_at_01 text DEFAULT (datetime('now','localtime')),
    created_at_02 text DEFAULT CURRENT_TIMESTAMP
);

-- Test the function of the default values
INSERT INTO my_table (comment) VALUES ('hello world');

SELECT * FROM my_table;

id          comment      created_at_01        created_at_02      
----------  -----------  -------------------  -------------------
1           hello world  2019-12-09 18:00:12  2019-12-09 17:00:12

2. Load this table into QGIS
3. Start editing
4. Add a Feature
5. -> Form is prefilled with default-value function

Post on gis.stackexchange

QGIS and OS versions

• QGIS 3.4 LTR (3.4.14 on Windows 10 and Linux / 3.4 on OSGeoLive 13)
• QGIS 3.10 (Windows 10)

Tried Solutions

• with "sql-insert" everything works as exepected
• same behaviour on different workstations
• same behaviour for geopackage, sqlite- and spatialite-databases
• same behaviour with or whitout geometry
• same behaviour in QGIS 3.4.7 (LTR) and 3.10
• same behaviour in Windows and Linux
• in spatialite InvalidateLayerStatistics(); and UpdateLayerStatistics(); does not help.
• Project Properties -> Data Source -> Check "Evaluate default values on provider side".

Additional context

Easiest workaround: Set the default value as well in the field widget. Layer Properties -> Attributes Forms -> field -> Default Value now()

maybe relevant commit 0ae610c

[elpaso]

Just to clarify: the fact that the form shows the default value clauses is the expected behavior, the bug is that when the layer is saved to the backend, the default values are stored verbatim instead of running the functions server side.

Also, the bug affects (at least) two different providers: OGR and spatialite.

[elpaso]

To clarify even more: when the default value source is the provider (like it is in this case) the expression is evaluated server/backend side, there is no way to show the actual value until the layer is saved.

Exception is postgis provider, that has a more complicated logic.