daviaws

Need help with :ets.match - I always end up with an empty list []

I’m writing a module to test ets match.
It would to store client consume by month/year.

I had try to follow match spec… I even tried to do automagic translate of elixir functions with GitHub - ericmj/ex2ms: :ets.fun2ms for Elixir, translate functions to match specifications · GitHub

nonetheless I always end up with an empty list []

Please… someone help me with list_period method…

defmodule ETS.Consume do
  @moduledoc """
  Consume tasks

    r ETS.Consume

    ETS.Consume.scenario()

    table = ETS.Consume.start()
    ETS.Consume.populate(table)
    ETS.Consume.list(table, "12345678901")
    ETS.Consume.list_period(table, "12345678901", 2, 2021, 10, 2021)
  """

  import Ex2ms

  @table :cons
  @opts [:ordered_set, :protected]
  def start do
    :ets.new(@table, @opts)
  end

  def insert(ref, cpf_cnpj, mes, ano, consumo) do
    key = {cpf_cnpj, mes, ano}

    :ets.insert(ref, {key, consumo})
  end

  def list(table, cpf_cnpj) do
    :ets.match(table, {{cpf_cnpj, :"$1", :"$2"}, :"$3"})
  end

  def list_period(table, cpf_cnpj, mes_inicio, ano_inicio, mes_fim, ano_fim) do
    pattern = [{{{:"$1", :"$2", :"$3"}, :"$4"}, [{:<, :"$2", 2}], [true]}]

    :ets.match(table, pattern)
  end

  def populate(table) do
    insert(table,  "12345678901", 1, 2021, 100)
    insert(table, "12345678901", 2, 2021, 200)
    insert(table, "12345678901", 3, 2021, 300)
    insert(table, "12345678901", 4, 2021, 200)
    insert(table, "12345678901", 5, 2021, 300)
    insert(table, "12345678901", 6, 2021, 350)
    insert(table, "12345678901", 7, 2021, 200)
    insert(table, "12345678901", 8, 2021, 100)
    insert(table, "12345678901", 9, 2021, 500)
    insert(table, "12345678901", 10, 2021, 300)
    insert(table, "12345678901", 11, 2021, 200)
    insert(table, "12345678901", 12, 2021, 310)
    insert(table, "12345678902", 1, 2021, 310)
  end

  def scenario do
    table = ETS.Consume.start()
    ETS.Consume.populate(table)
    # ETS.Consume.list(table, "12345678901")
    ETS.Consume.list_period(table, "12345678901", 2, 2021, 10, 2021)
  end

  def test() do
    fun do {{ cpf_cnpj, mes, ano }, consumo} = arg when mes < 2 -> true end
  end
end

12 comments

#ets

0 567 12

2023-12-27 22:26:57 UTC

Marked As Solved

daviaws

Complete solution thank to @al2o3cr answer

defmodule ETS.Consume do
  @moduledoc """
  History by key, month, age, value

    r ETS.Consume

    ETS.Consume.scenario()

    table = ETS.Consume.start()
    ETS.Consume.populate(table)
    ETS.Consume.list(table, "12345678901")
    ETS.Consume.list_period(table, "12345678901", 2, 2021, 10, 2021)
  """
  @table :cons
  @opts [:ordered_set, :protected]
  def start do
    :ets.new(@table, @opts)
  end

  def index(age, month) do
    age * 100 + month
  end

  def insert(ref, key, month, age, bytes) do
    index = index(age, month)
    key = {key, index, age, month}

    :ets.insert(ref, {key, bytes})
  end

  def list(table, key) do
    :ets.match(table, {{key, :_, :"$1", :"$2"}, :"$3"})
  end

  def list_period(table, key, begin_month, begin_age, end_month, end_age) do
    begindex = index(begin_age, begin_month)
    endex = index(end_age, end_month)

    # :ets.fun2ms(
    #   fn {{key, index, month, age}, bytes} = _entry when
    #     key == "12345678901" and
    #     index >= 202301 and index <= 202312 ->
    #         {month, age, bytes}
    # end)
    match_spec = [
      {{{:"$1", :"$2", :"$3", :"$4"}, :"$5"},
       [
         {:andalso, {:andalso, {:==, :"$1", key}, {:>=, :"$2", begindex}},
          {:"=<", :"$2", endex}}
       ], [{{:"$3", :"$4", :"$5"}}]}
    ]


    :ets.select(table, match_spec)
  end

  def populate(table) do
    insert(table,  "12345678901", 1, 2021, 100)
    insert(table, "12345678901", 2, 2021, 200)
    insert(table, "12345678901", 3, 2021, 300)
    insert(table, "12345678901", 4, 2021, 200)
    insert(table, "12345678901", 5, 2021, 300)
    insert(table, "12345678901", 6, 2021, 350)
    insert(table, "12345678901", 7, 2021, 200)
    insert(table, "12345678901", 8, 2021, 100)
    insert(table, "12345678901", 9, 2021, 500)
    insert(table, "12345678901", 10, 2021, 300)
    insert(table, "12345678901", 11, 2021, 200)
    insert(table, "12345678901", 12, 2021, 310)
    insert(table, "12345678901", 1, 2022, 410)
    insert(table, "12345678902", 1, 2021, 310)
  end

  def scenario do
    table = ETS.Consume.start()
    ETS.Consume.populate(table)
    # ETS.Consume.list(table, "12345678901")  |> dbg()
    ETS.Consume.list_period(table, "12345678901", 1, 2021, 9, 2021)
  end
end

Post #12

Also Liked

al2o3cr

There’s an unfortunate overlap in terminology: :ets.match takes a “match pattern”, not a match specification. The documentation for :ets.select/2 demonstrates this:

ets:match(Table,{'$1','$2','$3'})

# is equivalent to

ets:select(Table,[{{'$1','$2','$3'},[],['$$']}])

Demo:

iex(1)> tab = :ets.new(:foo, [:ordered_set])
#Reference<0.3893230368.2635726851.91982>

iex(3)> :ets.insert(tab, {{"a", 1, "b"}, "c"})
true

iex(4)> :ets.insert(tab, {{"d", 2, "e"}, "f"})
true

iex(6)> :ets.select(tab, [{{{:"$1", :"$2", :"$3"}, :"$4"}, [{:<, :"$2", 2}], [:"$_"]}])
[{{"a", 1, "b"}, "c"}]

Post #8