6

Is there any way to use QGIS variable values in QGIS query builder?

I would like to create a dynamic query which will load data from PostGIS based on a string value which equals the QGIS project filename. Like this:

"project_name" =  base_file_name(  @project_filename )
2
  • 3
    Where did you want to input your query ? is it for filtering what is fetched from the database or for selecting in a layer or for creating a query layer or ...
    – J.R
    Sep 28 at 8:52
  • The "Query builder" is one for filtering data fetched from the database.
    – etrimaille
    Sep 28 at 10:06
7

You need to use a QGIS Python Macro. QGIS Expression is not supported in the Query Builder.

Go in Project properties then Macros, the code is under the screenshot :

Project properties macro

Python code to use, you need to replace the layer_id variable :

from qgis.core import QgsProject
    
def openProject():
    project = QgsProject.instance()
    base_name = project.baseName()

    # Replace by the layer ID you need to filter, print(iface.activeLayer().id()) to have it
    layer_id = "observations_4a0f00d1_eba6_41b7_b196_1ee04ff3d50e"

    layer = project.mapLayer(layer_id)
    layer.setSubsetString("\"project_name\" = '{}'".format(base_name))

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  • why two functions closeProject() and saveProject() are required?
    – Taras
    Sep 28 at 11:09
  • 1
    They are not required. They are just by default when you open this tab in QGIS, with an empty project : openProject, saveProject and closeProject. I will remove.
    – etrimaille
    Sep 28 at 11:21
  • it runs on error: Layer tablename: ERROR: column "somestring" does not exist LINE 1: ...T * FROM "public"."tablename" WHERE project_name = Somestring... I guess because the last row above inserting it without ' character.
    – Tamas Kosa
    Sep 28 at 15:38
  • Yes, I have fixed colunm and string formatting with " and '. You can still upvote if it works. I was trying with a integer sorry.
    – etrimaille
    Sep 28 at 15:45
  • 1
    Brilliant, it works
    – Tamas Kosa
    Sep 28 at 15:54

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