Fast XLSX Exporter

Installation

Add fast_xlsx_exporter to your mix.ex deps:

def deps do
  [
    {:fast_xlsx_exporter, "~> 0.2.2"}
  ]
end

Explanation

Elixlsx was fine, until really huge exports appeared. Then it took more and more time to generate xlsx reports. And RAM.

So, being really primitive (8 hour at night from scratch knowing nothing about xlsx) this library does not store document in memory. It writes straight to file system.

Some example:

rows = [[1, 2, 3, 10], [4, 5, 6], [7, 8, 9]]

context = FastXlsxExporter.initialize()
context = Enum.reduce(rows, context, &FastXlsxExporter.put_row/2)
{:ok, document} = FastXlsxExporter.finalize(context)
File.write("/home/george/failures.xlsx", document)

See? Really simple thing, nothing special.

If you're looking for something that really supports xlsx, go with elixlsx.

Supported cell values

Numbers

Both float and integer values are supported and special form of {<float>, :percents} to write number as xlsx percent.

Example row:

[1, 12.5, {0.59, :percents}]

Strings

Strings could be written in two ways.

First one is straight (no special form). In this case strings are written sequentially to shared strings, which is RAM-friendly but bloats resulting xlsx file.

Second one requires special form of {<string>, :dictionary}. In this case strings are put into dictionary and are put into shared strings only once, but are stored in memory, which is good for limited set of values but can cause OOMKilled if strings are random.

Example rows:

# first row
["Vladimir Putin", "Donald Trump", "Literally Hitler"]
# second row
[{"some_string", :dictionary}, {"some_other_string", :dictionary}, {"some_string", :dictionary}]
# third row
["wow!", {"some_other_string", :dictionary}, "yay!"]

Date and time

Both %Date{} and %NaiveDateTime{} are rendered as dates (not strings).

Example row:

[~D[1905-12-11], ~D[2020-04-09], ~N[2020-04-09 12:00:00]]