Using Conditional branch algorithm in QGIS Graphical Modeller

Question

I have a question regarding using the Conditional Branch algorithm in the Graphical Model Builder.

I am building a rather complicated model with many branches but not every branch needs to be used every time. So I want to use the Conditional Branch algorithm to check the "art" column of the attribute table from my input layer and to only run that branch if a given value is present, PX or QX in this particular case.

The model will have at least 15 branches when I am finished but usually only a few will be needed per job.

So, I need to use the Conditional Branch algorithm as a kind of if/else filter where if the value is present it runs the branch elsewise it ignores that branch and moves on to the next one.

How do I set up the Conditional Branch so that it ignores that branch unless the value is present?

(Pic isn't my main model, just an example)

basic model

Answer 1

I've created a model with an input point layer.

A conditional branch with two conditions:

1. If there is an A in the art column: The points get buffered
2. If not it will create rectangles around the points.

Start by renaming the layer to inlayer

Create a conditional branch with the condition aggregate(layer:='inlayer', aggregate:='count', expression:="art", filter:="art" IN('A'))>0

(IN Operator)

It will count the number of values in the art column where the value is A. If more than 0 the branch will be True.

Create another branch with the opposite condition: aggregate(layer:='inlayer', aggregate:='count', expression:="art", filter:="art" IN('A'))<1

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Use the branches as dependecies to the next algorithms: enter image description here

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