Elixir: clean deps

Source: How to remove unused deps from mix.lock
This removes the unused files, as well as cleans mix.lock.

> mix deps.clean --unused --unlock

Elixir: rename_keys

Elixir equivalent of Clojure rename_keys()

  @doc """
  Returns the map with the keys in kmap renamed to the values in kmap.
  """
  def rename_keys(map, kmap) when is_map(map) and is_map(kmap) do
    for {key, value} <- map,
        into: %{},
        do: if(new_key = Map.get(kmap, key), do: {new_key, value}, else: {key, value})
  end

Elixir: if key exists: update, otherwise: assoc

Remember Clojure: if key exists: update, otherwise: assoc? Let's do that with Elixir.

  @doc """
  If `key` exists in `map`, updates its value (assumed to be a list) by concatenating `value`.
  If `key` does not exist in `map`, creates `{key => [value]}` in `map`.
  ## Examples

    iex(35)> Tap.Worker.update_conj!(%{a: [1]}, :a, 2)
    %{a: [1, 2]}

    iex(36)> Tap.Worker.update_conj!(%{a: [1]}, :b, 2)
    %{a: [1], b: [2]}

  """
  @spec update_conj!(map, any, any) :: map
  def update_conj!(map, key, value) when is_map(map) do
    Map.update(map, key, [value], fn
      existing_values when is_list(existing_values) ->
        existing_values ++ [value]

      existing_value ->
        raise(ArgumentError, "Value is not a list: #{inspect(existing_value)}")
    end)
  end

Elixir: map to struct

Courtesy of Jose Valim: (https://groups.google.com/forum/#!msg/elixir-lang-talk/6geXOLUeIpI/L9einu4EEAAJ).

  def to_struct(kind, attrs) do
    struct = struct(kind)

    Logger.debug("attrs = #{inspect(attrs)}")

    Enum.reduce(Map.to_list(struct), struct, fn {k, _}, acc ->
      case Map.fetch(attrs, k) do
        {:ok, v} -> %{acc | k => v}
        :error -> acc
      end
    end)
  end

macOS: Docker volumes and Minikube

This morning I decided to replace Docker Desktop on my mac with the Hyperkit + Minikube combo like explained in Run Docker without Docker Desktop on macOS.

Volumes

However, some file mounted through a volume in docker-compose invariably resulted in a directory being created in the container instead of a file.
docker-compose.yaml

version: "3.8"
services:
  postgres:
    container_name: oss-postgres
    image: postgres:14-alpine
    stdin_open: true
    tty: true
    restart: always
    ports:
      - 5432:5432
    volumes:
      - ./postgres/postgres.sh:/docker-entrypoint-initdb.d/postgres.sh
    environment:
      POSTGRES_PASSWORD: "xxx"

logs

oss-postgres  | /usr/local/bin/docker-entrypoint.sh: running /docker-entrypoint-initdb.d/postgres.sh
oss-postgres  | /usr/local/bin/docker-entrypoint.sh: line 169: /docker-entrypoint-initdb.d/postgres.sh: Is a directory
oss-postgres exited with code 126

It appears that the volumes need being created in the Minikube VM beforehand (source: Replace Docker Desktop with Minikube and Hyperkit on macOS), like in:

> minikube stop
> minikube start --mount --mount-string="/Users/jerome/src/boss/:/Users/jerome/src/boss/" --memory 4096 --cpus 4

Ports

Any service previously reachable through localhost by port forwarding is now available by using docker.dev, mapped to minikube ip in /etc/hosts. 

NOTE

Never use .local domain on macOS, or DNS resolving will become awfully slow: use for ex. docker.dev instead of docker.local for the hostname of the minikube ip, contrary to what the 1st article proposes.

Elixir: convert map to keywords list

iex(20)> Enum.reduce(%{"code" => 33, "kind" => 2, "servid" => 13}, [], fn {k, v}, acc -> acc ++ [{String.to_atom(k), v}] end)
[code: 33, kind: 2, servid: 13]

or

iex(23)> for {k, v} <- %{"code" => 33, "kind" => 2, "servid" => 13}, do: {String.to_atom(k), v}
[code: 33, kind: 2, servid: 13]

elixir-ls: /usr/local/bin/elixir: line 231: exec: erl: not found

Source: Elixir on Emacs: exec erl not found
If after installing elixir-ls in emacs, you get this error reported in *elixir-ls::stderr* buffer, then install exec-path-from-shell by using M-x package-list-packages.

PostgreSQL: Get a column value corresponding to the min of another column

Source: Understanding Window Functions

Purpose: Get a column value corresponding to the min of another column (i.e. both values must belong to the same row)
E.g. Let's say we have columns a,b,c,b. We want a,b matching min(c) while partitioning by d.

 

crmmbqt=# create table demo (a int, b int, c int, d int);

 

crmmbqt=# insert into demo (a, b, c, d) values (1,2,1,1), (2,1,3,1), (3,4,5,2), (4,3,4,2);

INSERT 0 4

Time: 6.106 ms

crmmbqt=# select * from demo;

┌───┬───┬───┬───┐

│ a │ b │ c │ d │

├───┼───┼───┼───┤

│ 1 │ 2 │ 1 │ 1 │

│ 2 │ 1 │ 3 │ 1 │

│ 3 │ 4 │ 5 │ 2 │

│ 4 │ 3 │ 4 │ 2 │

└───┴───┴───┴───┘

(4 rows)

crmmbqt=# select first_value(a) over (partition by d order by c) as a, first_value(b) over (partition by d order by c) as b, c, d from demo;

┌───┬───┬───┬───┐

│ a │ b │ c │ d │

├───┼───┼───┼───┤

│ 1 │ 2 │ 1 │ 1 │

│ 1 │ 2 │ 3 │ 1 │

│ 4 │ 3 │ 4 │ 2 │

│ 4 │ 3 │ 5 │ 2 │

└───┴───┴───┴───┘

(4 rows)

NB: The use of first_value() is really important here.
For example, if you want to get max(c) instead of min(c), do not use last_value(a) but instead:

first_value(a) over (partition by d order by c desc)

crmmbqt=# select min(a) as a, min(b) as b, min(c), d from (select first_value(a) over (partition by d order by c) as a, first_value(b) over (partition by d order by c) as b, c, d from demo) as foo group by d;

┌───┬───┬─────┬───┐

│ a │ b │ min │ d │

├───┼───┼─────┼───┤

│ 1 │ 2 │ 1   │ 1 │

│ 4 │ 3 │ 4   │ 2 │

└───┴───┴─────┴───┘

(2 rows)

Git: Moving files to a new repository while preserving history

> git --version
git version 2.18.0

This method did not work for me: Move files from one repository to another, preserving git history
But this one did the trick: Moving Files and Directories to a New Repository in Git

Here is the list of commands used in order to extract the contents of the perl/ directory from the connectmv repo. into the ss-sms-vas repo.:

> mkdir cloneA
> cd cloneA/
> git clone git@github.com:<MY_TEAM>/connectmv.git
> cd connectmv/
> git subtree split --prefix perl/ --branch my-subtree
> git checkout my-subtree
> git remote add repoA git@github.com::<MY_TEAM>/ss-sms-vas.git
> git pull repoA main --allow-unrelated-histories

> git push -u repoA my-subtree:main
> cd ../../
> rm -rf cloneA/

> cd ss-sms-vas/
> git pull
> git lol lib/MBQT/mod_perl/AbstractVas.pm 
* 72be224f (Thu Jan 7 18:32:47 2021 Jerome G) PLTBUGS-8700: exploded USSD CDR per process
* 680a9ff2 (Thu Jan 7 13:51:45 2021 Jerome G) PLTBUGS-8700: removed unlock
...