move_all_children_of_a_location.yml

# Move all children of location A to location B, taking into account that:
# - the children could be many thousands. To cope, we avoid both loading all contents in memory at the same time, and
#   creating huge db transactions. In order for that to happen, the migration should be run with `--no-transactions`;
# - live traffic to the website should not be disrupted while the migration runs. To achieve that, we sleep 10 seconds
#   between every action, which should prevent overloading either the database or the search engine;
# - some children contents could already have a location in B. In that case, we just remove their location in A

# 1: we use references to keep the migration tidier
-
    type: reference
    mode: set
    identifier: old_parent_location
    value: 123456 # change this!
-
    type: reference
    mode: set
    identifier: new_parent_location
    value: 3456789 # change this!

# 2: load all children locations
-
    type: location
    mode: load
    match:
        parent_location_id: 'reference:old_parent_location'
    expect: many
    references:
        -
            identifier: location_ids
            attribute: location_id

# 3: loop over children locations, and either move or remove them
-
    type: loop
    over: "reference:location_ids"
    steps:
        # In order to find if the child already has a .location in parent B, we need to do two loads
        -
            type: content
            mode: load
            match:
                location_id: 'loop:value'
            references:
                -
                    identifier: content_id
                    attribute: content_id
                    overwrite: true
        -
            type: location
            mode: load
            match:
                and:
                    - parent_location_id: 'reference:new_parent_location'
                    - content_id: 'reference:content_id'
            expect: any
            references:
                -
                    identifier: already_there
                    attribute: count
                    overwrite: true
        # carry out the removal operation if needed, and print a debug message
        -   type: reference
            mode: dump
            identifier: 'loop:value'
            label: 'removing location: '
            if:
                "reference:already_there":
                    gt: 0
        -
            type: location
            mode: delete
            match:
                location_id: 'loop:value'
            if:
                "reference:already_there":
                    gt: 0
        # otherwise, move the location, and print a debug message
        -
            type: reference
            mode: dump
            identifier: 'loop:value'
            label: 'moving location: '
            if:
                "reference:already_there":
                    lt: 1
        -
            type: location
            mode: update
            match:
                location_id: 'loop:value'
            parent_location_id: 'reference:new_parent_location'
            if:
                "reference:already_there":
                    lt: 1
        # give the DB and search engine some room to breathe
        -
            type: migration
            mode: sleep
            seconds: 10