Migration from source YML: implode all values of each array element nested inside an parent array We are trying to pull in some data from an outside source that serves JSON.

The structure of said json is like this:

[
    {
        "name":"something",
        "desc":"some kind of desc.",
        "tags": [
            {
                "order":"3",
                "displayName":"Tag1"
            },
            {
                "order":"13",
                "displayName":"Tags 101"
            },
            {
                "order":"28",
                "displayName":"Dogs"
            }
        ]
    }, ...

]


We want to implode all tags.displayName values into one string.  I'll use the body field as an example. 
In the UI, if you view the content, "body" would be:

Tag1|Tags 101|Dogs


In the "fields" section of my migration source yml file:

name: tagsCollection
label: "tagsCollection"
selector: tags


Then, in the process section of the YML file I've tried this:

body:
    plugin: concat
    delimiter: "|"
    source:
     - stepsCollection


I've also looked into the iterator plugin.  Nothing seems to click.

If I do this in the process section of the yml file:

body: stepsCollection


body will be "Array" in the UX.  So it is aware that there is an array in that var.

What am I missing??  Many thanks
The documentation examples of concat plugin use a flat, non-associative array of strings as source, you are trying to concat a nested array of JSON objects. You could try to subprocess your tags to only fetch/concat the displayName from them