I am pretty new to Qgis and a real beginner when it comes to working with expressions in Qgis. Maybe someone can help me with following problem:
I have several Layers (like Building + House) and each of them have specific attributes values that i want to filter. So my idea was to get an extra layer Test with the attribute value that i want to filter on the other layers and put a filter expression to the attribute value A in table category_1 of layer Test. Basically to avoid rewriting the filters for each layer all the time. But I dont know how to get it done. I tried it with get_feature and attribute() but in my Qgis 2.18 there is no help how such expressions have to look like. That makes it really hard if u have no clue. So how can I filter with the attribute value A in category_1 of layer the Test in the layer House ?