I am experimenting with live view uploads for the first time, and I was wondering what is the recommended way of doing customized upload validations.
My simple example: I have an interface to upload files to a certain directory, and I want to warn the users of duplicate file names in their upload before they hit the submit button. My consume_uploaded_entries/3 would catch these cases, but I am expecting larger files being uploaded, so some feedback earlier would be nice.
So I could evaluate my uploads assign against a list of existing files by…
… setting :valid to false in the appropriate Phoenix.LiveView.UploadEntry structs.
… generating an appropriate error list for errors in the Phoenix.LiveView.UploadConfig struct.
It feels a little bit like screwing around with Phoenix LiveView implementation internals. Is this the way to do it? Did I miss some kind of helper function?
But now I bumped into the issue: After evaluating the affected entries and setting appropriate errors, I am not allowed to use re-assign/3 the :upload key because it is a “reserved” one:
** (ArgumentError) :uploads is a reserved assign by LiveView and it cannot be set directly
(phoenix_live_view 1.0.0-rc.6) lib/phoenix_component.ex:1324: Phoenix.Component.validate_assign_key!/1
(phoenix_live_view 1.0.0-rc.6) lib/phoenix_component.ex:1275: Phoenix.Component.assign/3
So my initial reaction proved somewhat right: The LiveView authors do not want me to prod around in those internals.
But: What can I do now? What seems to be missing is an option for allow_uploads/3 for passing a custom validator function.
Here existing_files is a list containing application specific metadata structs. As you can see I use Map.put/3 to hack my way around the “reserved assign” restriction.
The function mark_duplicate_names/2 looks like this:
defp mark_duplicate_names(%Phoenix.LiveView.UploadConfig{} = upload, existing_names) do
processed_entries =
upload.entries
|> Enum.map(fn %Phoenix.LiveView.UploadEntry{} =
entry ->
if entry.client_name in existing_names do
Map.put(entry, :valid?, false)
else
entry
end
end)
upload
|> Map.put(:entries, processed_entries) # replace file entries
|> Map.put(
:errors,
Enum.map(processed_entries, fn %Phoenix.LiveView.UploadEntry{} = entry ->
if entry.valid? do
nil
else
{entry.ref, :name_duplicate}
end
end)
|> Enum.reject(fn val -> is_nil(val) end) # create a list of error tuples for all entries with error
)
end
Finally I implement a fourth error_to_string/1 function:
defp error_to_string(:name_duplicate), do: "A file with this name already exists"
Small update: In order to preserve the errors that got returned by Phoenix’ standard evaluation (size, type, upload count issues), I had to modify the function slightly.
defp mark_duplicate_names(%Phoenix.LiveView.UploadConfig{} = upload, existing_names) do
processed_entries =
upload.entries
|> Enum.map(fn %Phoenix.LiveView.UploadEntry{} =
entry ->
if entry.client_name in existing_names do
Map.put(entry, :valid?, false)
else
entry
end
end)
duplicate_name_errors =
Enum.map(processed_entries, fn %Phoenix.LiveView.UploadEntry{} = entry ->
previous_error? = Enum.any?(upload.errors, fn {ref, _msg} -> ref == entry.ref end)
if entry.valid? or previous_error? do
nil
else
{entry.ref, :name_duplicate}
end
end)
|> Enum.reject(fn val -> is_nil(val) end)
# Combine existing errors with additional ones evaluated here.
errors = upload.errors ++ duplicate_name_errors
upload
|> Map.put(:entries, processed_entries)
|> Map.put(:errors, errors)
end