Note: This package is now obsolete and is kept here for historical purposes as well as anyone who hasn't upgraded. Postgrex offers hstore support directly.

Ecto.Hstore adds Postgres Hstore compatibility to your Ecto models for storing sets of key/value pairs within a single PostgreSQL value. This can be useful in various scenarios, such as rows with many attributes that are rarely examined, or semi-structured data. Keys and values are simply text strings.

Hstore structures are represented by Elixir Maps.

Add Ecto.Hstore as a dependency in your mix.exs file.

defp deps do
  [{:postgrex, ">= 0.0.0"},
   {:ecto, "~> 0.7"},
   {:ecto_hstore, "~> 0.0.1"}]
end

After you are done, run mix deps.get in your shell to fetch the dependencies.

Enable Hstore through an ecto migration:

defmodule Repo.Migrations.EnableHstore do
  use Ecto.Migration

  def up do
    execute "CREATE EXTENSION hstore IF NOT EXISTS"
  end

  def down do
    execute "DROP EXTENSION hstore IF EXISTS"
  end
end

Add your desired Postgres hstore columns through a migration:

defmodule Repo.Migrations.CreateUsers do
  use Ecto.Migration

  def up do
    create table :users do
      add :flags, :hstore, null: false, default: ""
    end
  end

  def down do
    drop table(:users)
  end
end

Define your Ecto model's schema using the corresponding Ecto.Hstore type:

defmodule User do
  use Ecto.Model

  schema "users" do
    field :flags, Ecto.Hstore
  end
end

And now you're all set!

# Inserting a new user with flags is as simple as creating an Elixir Map:
user = Repo.insert %User{flags: %{key: "value"}}
user.flags #=> %{"key" => "value"}

# Updating the hstore value is as simple as `Dict.put`
flags = Dict.put(user.flags, "key2", "value2")
user = %User{user| flags: flags}
Repo.update user

query = from u in User,
          where: fragment("?->'?' = '?'", u.flags, "key2", "value2"),
          select: u

users = Repo.all(query) #=> [%User{flags: %{"key" => "value", "key2" => "value2"} ...]

Elixir Maps and Postgres Hstore types have a few important differences that users should be cautious of. The current behavior of these edge cases may change in future releases of Ecto.Hstore.

• Postgres Hstore does not allow null keys, whereas Elixir Maps do. Currently nil keys will not be serialized to Postgres.
• Postgres Hstore does not have an atom type. All keys are stored as strings. Therefore extra caution must be taken to ensure that an Elixir Map doesn't contain two converging keys (eg: %{:a => 2, "a" => 2}), because they will be consolidated to one string key "a" in a non-deterministic manner.
• Postgres Hstore only supports a single level of key/value pairs. Nested maps are not supported, and attempting to serialize nested maps will give undesirable results.

To contribute you need to compile Ecto.Hstore from source and test it:

$ git clone https://github.com/stavro/ecto_hstore.git
$ cd ecto_hstore
$ mix test

Copyright 2015 Sean Stavropoulos

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.