How to create block to list all children of an entity?

Question

I want to list all the nodes that have the currently viewed node as their parent.

To make this more tangible and less abstract, let's do an example:

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I have a content type Locations which has an Entity Reference field called parent_location with an unlimited number of values.

For example:

- USA (3)                             [country level]
  - New York (4)                        [state level]
    - New York City (6)                   [city level]
      - Central Park (8)                    [landmark level]
      - Empire State Building (9)           [landmark level]
      - Times Square (10)                   [landmark level]
  - Illinois (5)                        [state level]
    - Chicago (7)                         [city level]
      - Sears Tower (11)                    [landmark level]
      - That bean looking thing (12)        [landmark level]

So when I view the content for USA (3), I wanna list all the children, meaning New York (4) and Illinois (5).

When I view New York City (6) I want to list Central Park (8), Empire State Building (9), and Times Square (10).

I want these to show up when I view /node/6 and be clickable, so that I can browse this nested child/parent structure.

It's already possible by default to traverse UP on the tree. Meaning I can easily get from Times Square (10) all the way up to USA (3).

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However, I can't figure out how to list all children of the appropriate level!

I did create a block view called List Child Locations. And I've placed this view on the block Content. It shows up correctly, but it does not list the appropriate children.

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When it comes to editing my view, I have no clue what I'm doing or how...

I see there's two options:

admin/structure/views/view/list_child_locations/edit/block_1

and

admin/structure/views/view/list_child_locations/edit/entity_reference_1

I think I have to do something with contextual filters, while I'm in the Entity Reference Display. But I can't find anything that looks like what I need...

Out of all those many options, which one do I chose to make sure it does something like

SELECT * from Locations WHERE parent_location = %current_location% ?

What's the right settings for my entity display to only list the children?

Answer 1

Finally, I figured it out!

First, I learned more about contextual filters and relationships, and what they each mean and do (relationships basically relates to the FROM query, contextual filters to the WHERE query)

https://www.youtube.com/watch?v=mRWtpcUm9pI

Another user had a similar question and solved it like so:

https://www.drupal.org/project/views/issues/1724396

So all I had to do was:

/admin/structure/views/add

• show content of type "Locations"
• Create a block

Then under "advanced" add a contextual filter, check "parent_location (field_parent_location)", press the button to "Add and configure".

Then under "When no filter is available" say "provide a default value" and select "content ID from URL"

Hit apply, save the view.

Under /admin/structure/block place the block to the content region and make it visible for Locations.

This was super simple! :-)