DBKV

DBKV is a disk-based embedded key-value storage built on top of :dets. Inspired by CubDB's intuitive API.

Usage

Open a database

iex> {:ok, t} = DBKV.open(name: :my_table, data_dir: "tmp")
{:ok, :my_table}

iex> DBKV.open?(t)
true

Upsert a key-value pair

iex> DBKV.put(t, "greeting", "Hi")
:ok

iex> DBKV.get(t, "greeting")
"Hi"

Insert a key-value pair if it does not exist

iex> DBKV.put_new(t, "greeting", "Hello")
{:error, :exists}

iex> DBKV.get(t, "greeting")
"Hi"

iex> DBKV.put_new(t, "temperature", 32)
:ok

iex> DBKV.get(t, "temperature")
32

Update a key-value pair with a function

iex> DBKV.update(t, "greeting", "default", &(&1 <> "!!!"))
:ok

iex> DBKV.get(t, "greeting")
"Hi!!!"

iex> DBKV.update(t, "language", "default", &(&1 <> "!!!"))
:ok

iex> DBKV.get(t, "language")
"default"

Delete a key-value pair

iex> DBKV.delete(t, "greeting")
:ok

iex> DBKV.get(t, "greeting")
nil

Persistence across restart

iex> DBKV.close(t)
:ok

iex> DBKV.open?(t)
false

iex> DBKV.open(name: t, data_dir: "tmp")
{:ok, :my_table}

iex> DBKV.get(t, "temperature")
32

Initialize the table

iex> DBKV.init_table(t, [a: 0, b: 1, c: 2, d: 3, e: 4])

Select records

By key range

iex> DBKV.select_by_key_range(t, :b, :d)
[b: 1, c: 2, d: 3]

By match spec

iex> require Ex2ms

iex> match_spec = Ex2ms.fun do {k, v} = kv when :b <= k and k <= :d -> kv end
[{{:"$1", :"$2"}, [{:andalso, {:"=<", :b, :"$1"}, {:"=<", :"$1", :d}}], [:"$_"]}]

iex> DBKV.select_by_match_spec(t, match_spec)
[b: 1, c: 2, d: 3]

Troubleshooting

Argument Error

When a table is not open, underlying :dets will raise ArgumentError. Please make sure that the table is opened with a correct name.

iex> DBKV.get(:nonexistent_table, "temperature")
** (ArgumentError) argument error
    (stdlib 3.15.1) dets.erl:1259: :dets.lookup(:nonexistent_table, "temperature")
    (dbkv 0.2.0) lib/dvkv.ex:131: DBKV.get/3

Use :dets functions

DBKV is a thin wrapper of :dets. You can mix and match with any :dets functions if you wish.

iex> :dets.info(t)
[
  type: :set,
  keypos: 1,
  size: 0,
  file_size: 5464,
  filename: 'tmp/my_table.db'
]

:invalid_objects_list error

When a table is initialized inappropriately, the table may return {:error, :invalid_objects_list}. In such a case, re-opening the table will fix it.

iex> DBKV.init_table(t, ["invalid object list"])
{:error, :invalid_objects_list}

iex> DBKV.get(t, :a)
** (CaseClauseError) no case clause matching: {:error, :invalid_objects_list}
    (dbkv 0.2.0) lib/dvkv.ex:131: DBKV.get/3

iex> DBKV.close(t)
{:error, :invalid_objects_list}

iex> {:ok, t} = DBKV.open(name: :my_table, data_dir: "tmp")
dets: file "tmp/Elixir.DBKV.db" not properly closed, repairing ...
{:ok, :my_table}

iex> DBKV.all(t)
[]

Installation

DBKV can be installed by adding dbkv to your list of dependencies in mix.exs:

def deps do
  [
    {:dbkv, "~> 0.2"}
  ]
end

Documentation can be found at https://hexdocs.pm/dbkv.

Alternativess

• CubDB
• dets