[GIS] QGIS 3: How to rename attribute/field names for Geopackage Layer

fields-attributesgeopackageqgis-3

Issue: I need to rename several attributes/fields in a geopackage layer. How to do this?

Linked Issue: there are numerous pages on how to rename the attributes/fields of a shapefile. However there do not seem to be any pages specifically addressing the modification of attributes to geopackage layers, except a few about using Python scripts. Perhaps what is assumed at the moment (Feb 2019) is that you must be able to do Python programming in order to modify fields in Geopackage layers?

Before tagging this as a duplicate, please make sure you are not presuming that I am trying to modify a shapefile. I am trying to modify a geopackage layer.

Best Answer

You can rename, drop, add, reorder Geopackage fields using QGis 3.x as follows: Processing > Toolbox > Vector table > Refactor fields. This will output a new Geopackage.

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[GIS] How to delete fields from a Geopackage attribute table

GeoPackage is a SQLIte database, So you can edit the table with a program for manage databases.

Per example, you could to use "DBeaver", or you could to use "SQLite Expert Personal" (freeware).

With SQLite Expert you could to delete and reorder fields.

QGIS GeoPackage – Meaning of Maximum Field Length of 0

If you create a GeoPackage table by setting a max length for an attribute then the corresponding SQL CREATE statement will look like this:

CREATE TABLE "temp" ( "fid" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "geometry" POINT, "foo" TEXT(3))

For SQLite/GeoPackage database number 3 in TEXT(3) does not have any meaning. It is still possible to store longer strings into that field. The real maximum length is defined at compile time with "SQLITE_MAX_LENGTH" and by default it allows 1 billion (1 thousand million or 1,000,000,000) single byte characters https://www.sqlite.org/limits.html.

However, QGIS does read and interpret the string length in the CREATE statement and it is impossible to store any longer strings with QGIS tools. If user edits data for example directly with SQL to contain longer strings like foo='bbbbb' QGIS shows the data as it is stored into GeoPackage. However, when I tried to edit that attribute into bbbb with QGIS it actually changed the value into NULL obviously because bbbb in longer than 3 characters. I think this is a bug in QGIS. The GeoPackage standard defines

The optional maxchar_count defines the maximum number of characters in the string. If not specified, the length is unbounded. The count is provided for informational purposes, and applications MAY choose to truncate longer strings if encountered. When present, it is best practice for applications to adhere to the character count.

So it would have been OK to truncate bbbb into bbb but not to set it into NULL.

Strings without max length do not take any more space in SQLite/GeoPackage than strings with max length. If there is no real reason to limit the attribute length I would say that it is safer to not set any limits. Some reasons to limit the length include a need to export data into shapefiles (max string length 254 characters) or if the attribute will be used in a form as a postal address or something like that.

Best Answer

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[GIS] How to delete fields from a Geopackage attribute table

QGIS GeoPackage – Meaning of Maximum Field Length of 0

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