Non-standard source for a relationship

[kbaird]

Hi. Let's say I have a Product, with a tag_ids field of type {:array, :string}.

I'd like to construct a normal-appearing tags relationship in my ProductView, such that the tags derive not from a regular has_many relationship, but rather any Tag whose uuid primary_key is in that product.tag_ids array.

Is there any reasonable way to do this?

[kbaird]

In case anyone's curious, a potential solution in the schema file:
field :tags, {:array, :map}, virtual: true

  def inject_tags_from_tag_ids(product) do
    tag_ids = product.tag_ids || []
    tags = for id <- tag_ids, do: %{id: id}
    %{product | tags: tags}
  end

Then adding tags: TagView to relationships in the View seems to work OK, as long as you pass your product through the function at some point.

NOTE: edited to remove incorrect :include from View code example.

[jeregrine]

This will work temporarily. I think a solution for this might be to allow view functions to override relationships as well to pre-process them. But I'm open to suggestions for this api as you're use case isn't unique and we'll likely see it come up again.

…

On Wed, Oct 3, 2018 at 2:18 PM, Kevin C. Baird ***@***.***> wrote: In case anyone's curious, a potential solution: field :tags, {:array, :map}, virtual: true def inject_tags_from_tag_ids(product) do tag_ids = product.tag_ids || [] tags = for id <- tag_ids, do: %{id: id} %{product | tags: tags} end Then adding tags: {TagView, :include} to relationships in the View seems to work OK. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#136 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAGKFsEeiRKtygqiJUaRJqoXUliN8WDxks5uhQ2EgaJpZM4XE_aj> .

[kbaird]

Just spitballing on things that would've seemed easier to me.

here's one idea:

def relationships do
  [
    # other entries...
    tags: {:tag_ids, &tags_from_ids/1}
  ]
end

defp tags_from_ids(tag_ids) do
  for id <- tag_ids, do: %{id: id, type: "tags"}
end

The idea being that :tag_ids is the name of the field that is the source of the data, and &tags_from_ids/1 is the function to transform said data.

The particulars above could be modified to allow specifying TagView somewhere as well, etc. If that's easier.

[kbaird]

You could also lock it down more with

def relationships do
    [
    # other entries...
    tags: [ids: :tag_ids, type: "tags"]
  ]
end

That's less flexible, intended only for an input that is known to be a list of IDs (as is true for us). I'm not sure what else you might be getting in for a relationship, anyway.

[kbaird]

FYI, this is no longer a priority for our specific project.

[jherdman]

Ha! I was just contemplating this issue. Many thanks for the heads up. I'll close this issue then.