Guided Offline Editing is a plugin for QGIS to help users with offline edition of PostgreSQL/Postgis layers.
- Project homepage: https://github.com/ygversil/qgis-guided-offline-editing
- Documentation: https://qgis-guided-offline-editing.readthedocs.io/en/latest/
Before the plugin can be used, "power users" (may be database administrators or gis administrator) need to prepare one or more projects for offline edition and save them into PostgreSQL.
Once some projects have been preprared, "normal users" can use the plugin to
see the list of available projects, pick one, and click the download button to
start offline editing. No need to worry about selecting correct layers to
download offline, just click Download.
Once back online, the plugin can be used to upload changes, just click the
Upload button.
Before the plugin can be used, a "power user" prepares one or more projects for editing. For example, it may be a project to collect survey data about wetlands. He or she:
- creates tables in PostgreSQL/Postgis, trying to be as close as possible to normal forms (QGIS won't allow fully normal database design, more details on this later) and with as many constraints as possible to ensure data consistency,
- loads them as layers in QGIS,
- creates in QGIS relationships between these layers,
- designs forms in QGIS to edit these layers with as much details as possible (field validation, error messages, and so on),
- set a special variable named
offlineon each layer that needs to be downloaded for offline editing, - save the project in PostgreSQL, in a known schema.
A "normal user" (who may also be a "power user" during the aforementioned preparation step) who wants to enter data about wetlands then just need to launch the plugin, select the wetland project, and click the download button.
The result is a single GeoPackage file containing both the project and the layers (saving a project in a GeoPackage has been introduced in QGIS 3.8).
He or she can now edit the layers offline and, when back online, launch the plugin again and click the upload button to synchronize the layers online.
Since this plugin saves QGIS projects in GeoPackage files, QGIS 3.8 or later is required, and this is the only software requirement.
In a multi-user context (eg. an organization), for each user to be able to
connect to PostgreSQL and open projects and layers, each user must store its
PostgreSQL credentials in QGIS authentication database under a configuration
with the same ID for all users. For example, if orgldap is the authid
to be shared across all users, the user A must store its PostgreSQL credentials
with this specific authid (username: usera, password: secreta, authid:
orgldap), and user B must also use the same authid (username: userb,
password: secretb, authid: orgldap). Under no circumstances you should
let the authid to be automatically generated.
See the following link for more information: https://docs.qgis.org/3.4/en/docs/user_manual/auth_system/auth_overview.html
PostgreSQL connection information must be provided as QGIS settings, in QGIS
INI file (either the global one, or the QGIS3.ini file in each user
folder), under a [Plugin-GuidedOfflineEditing] section. Possible values in
this section are:
host: PostgreSQL host (default:localhost),port: PostgreSQL port (default:5432),authcfg: configuration ID in QGIS authentication database where PostgreSQL credentials are stored (default:authorg),sslmode:enabledordisableddepending whether SSL is used to connect to PostgreSQL (default:disabled),dbname: PostgreSQL database where QGIS projects are saved (default:orgdb),schema: PostgreSQL schema where QGIS projects are saved (default:qgis).
Here is an example configuration tu put in QGIS3.ini file:
[Plugin-GuidedOfflineEditing] host=db.priv.acme.org port=5432 authcfg=acmeaut dbname=acmedb schema=qgis sslmode=disabled
If you are deploying QGIS on multiple computer, you can put this configuration
in a global INI file, (eg. qgis_acme_sttings.ini) and set the
QGIS_GLOBAL_SETTINGS_FILE environment variable. See the following link for
more information:
https://docs.qgis.org/3.4/en/docs/user_manual/introduction/qgis_configuration.html#deploying-qgis-within-an-organization
Finally, care must be taken that each user has sufficient permissions to edit
relevant tables (SELECT, INSERT, UPDATE, DELETE). The easiest
way to achieve this is to create a role (a PostgreSQL user with NOLOGIN
permission), grant correct permissions to this role on all tables that need to
be edited, and assign each actual user to this role.
See the following link for more information: https://www.postgresql.org/docs/current/role-membership.html
One important caveat is that each table to be edited offline must have an integer primary key. Even if you have another natural primary key, if that key is not an integer, then you cannot use it as a primary key: make it a unique column.
Another limitation is that you cannot use all PostgreSQL data types for columns. For example, you cannot use one of the range types for a column (min-max in the same column): QGIS will not recognize the type, and thus a range column won't show up in form. In this example, use two columns instead, one for min and one for max.
On the other hand, QGIS automatically generated forms cannot embrace the whole power of SQL constraints. For example, you may have a database constraint that says: "if column A is filled, then column B must be filled too". But the automatic form in QGIS cannot enforce this constraint, and thus will let user enter a value for field A and no value for field B. To work around this limitation, documentation is especially important. Each field in the form must be documented to warn user about extra constraints.
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.