How to use UUID Generator in Qgis 2

Question

I try to generate a UUID (edit widget) for a vector shapefile in qgis 2 but the field value is always NULL. Does the field requirea specific datatype? I used integer. In the manual I found the info "what uuid-generator is" but not how to use it.

Thanks for any help, Patrick

Answer 1

I struggled for a bit to figure this out, too...

First off, it is important to understand what is a UUID (or GUID)?

GUIDs are usually stored as 128-bit values, and are commonly displayed as 32 hexadecimal digits with groups separated by hyphens, such as {21EC2020-3AEA-1069-A2DD-08002B30309D}. GUIDs generated from random numbers sometimes contain 6 fixed bits saying they are random and 122 random bits;

As far as QGIS is concerned, this would be a 36 character string that will look something like 3a2a47bf-ccaf-4aa9-8100-cb3abceec3e7, so you would not be able to use a INT field type.

Next, using the UUID Generator widget is a "manual" process that edits a single record at a time. To do so:

1. Set your Properties-> Fields-> Edit Widget is set to "UUID generator".
2. Open your attribute table
3. Toggle on edit mode
4. Double-click in the empty field (set in step 1) to generate a new UUID for that record.

If what you are really after is a way to automatically generate UUID's for all features, @NathanW modified this 2011 code to work with QGIS 2:

import uuid
fieldname = 'UUID' # set the name of your field to update

layer = qgis.utils.iface.activeLayer() # get the active layer from the TOC
layer.startEditing() # start editing

iter = layer.getFeatures() # get all features from the layer
for feat in iter: # iterate over features
    feat[fieldname] = str(uuid.uuid4()) #fill field with GUID
    layer.updateFeature(feat) #update the attribute value

layer.commitChanges() # save edits to the layer

Then, do the following:

1. Highlight the layer to update (in the TOC)
2. Open up the Python Console,
3. Press the "Show Editor" button,
4. Paste this code into the Python Console,
5. Change the FIELDNAME variable to match the name of your field in your layer,
6. Press the "Run script" button.