Flop is an Elixir library that applies filtering, ordering and pagination parameters to your Ecto queries.
- offset-based pagination with
offset
/limit
orpage
/page_size
- cursor-based pagination (aka key set pagination), compatible with Relay pagination arguments
- ordering by multiple fields in multiple directions
- filtering by multiple conditions with various operators on multiple fields
- parameter validation
- configurable filterable and sortable fields
- join fields
- compound fields
- query and meta data helpers
- Relay connection formatter (edges, nodes and page info)
- UI helpers and URL builders through Flop Phoenix.
This library has been used in production for a while now. Nevertheless, there may still be API changes on the way to a more complete feature set.
Add flop
to your list of dependencies in mix.exs
:
def deps do
[
{:flop, "~> 0.16.1"}
]
end
If you want to configure a default repo, add this to your config file:
config :flop, repo: MyApp.Repo
Alternatively, you can add a configuration module. For more information, refer to the Flop module documentation.
To configure the sortable and filterable fields, derive Flop.Schema
in your
Ecto schema. While this step is optional, it is highly recommend, since the
parameters you will pass to the Flop functions will come from the user side and
should be validated. Deriving Flop.Schema
will ensure that Flop only
applies filtering and sorting parameters on the configured fields.
defmodule MyApp.Pet do
use Ecto.Schema
@derive {
Flop.Schema,
filterable: [:name, :species],
sortable: [:name, :age, :species]
}
schema "pets" do
field :name, :string
field :age, :integer
field :species, :string
field :social_security_number, :string
end
end
You can also define join fields, compound fields, max and default limit, and more. See the Flop.Schema documentation for all the options.
You can use Flop.validate_and_run/3
or Flop.validate_and_run!/3
to validate
the Flop parameters, retrieve the data from the database and get the meta data
for pagination in one go.
defmodule MyApp.Pets do
import Ecto.Query, warn: false
alias Ecto.Changeset
alias Flop
alias MyApp.{Pet, Repo}
@spec list_pets(Flop.t()) ::
{:ok, {[Pet.t()], Flop.Meta.t}} | {:error, Changeset.t()}
def list_pets(flop \\ %Flop{}) do
Flop.validate_and_run(Pet, flop, for: Pet)
end
end
The for
option sets the Ecto schema for which you derived Flop.Schema
. If
you didn't derive Flop.Schema as described above and don't care to do so,
you can omit this option (not recommended, unless you only deal with internally
generated, safe parameters).
On success, Flop.validate_and_run/3
returns an :ok
tuple, with the second
element being a tuple with the data and the meta data.
{:ok, {[%Pet{}], %Flop.Meta{}}}
Consult the docs for more info on the
Meta
struct.
If you prefer to validate the parameters in your controllers, you can use
Flop.validate/2
or Flop.validate!/2
and Flop.run/3
instead.
defmodule MyAppWeb.PetController do
use MyAppWeb, :controller
alias Flop
alias MyApp.Pets
alias MyApp.Pets.Pet
action_fallback MyAppWeb.FallbackController
def index(conn, params) do
with {:ok, flop} <- Flop.validate(params, for: Pet) do
pets = Pets.list_pets(flop)
render(conn, "index.html", pets: pets)
end
end
end
defmodule MyApp.Pets do
import Ecto.Query, warn: false
alias Flop
alias MyApp.Pets.Pet
alias MyApp.Repo
@spec list_pets(Flop.t()) :: {[Pet.t()], Flop.Meta.t}
def list_pets(flop \\ %Flop{}) do
Flop.run(Pet, flop, for: Pet)
end
end
If you only need the data, or if you only need the meta data, you can also
call Flop.all/3
, Flop.meta/3
or Flop.count/3
directly.
If you didn't configure a default repo as described above or if you want to override the default repo, you can pass it as an option to any function that uses the repo:
Flop.validate_and_run(Pet, flop, repo: MyApp.Repo)
Flop.all(Pet, flop, repo: MyApp.Repo)
Flop.meta(Pet, flop, repo: MyApp.Repo)
# etc.
See the docs for more detailed information.
Flop is built to handle parameters generated by a user. While you could manipulate those parameters and add additional filters when you receive them, it is recommended to cleanly separate the parameters you get from the outside and the parameters that your application needs to add internally.
For example, if you need to scope a query depending on the current user, it is
preferred to add a separate function that adds the necessary WHERE
clauses:
def list_pets(%{} = args, %User{} = current_user) do
Pet
|> scope(current_user)
|> Flop.validate_and_run(flop, for: Pet)
end
defp scope(q, %User{role: :admin}), do: q
defp scope(q, %User{id: user_id}), do: where(q, user_id: ^user_id)
To add additional filters that can only be used internally without exposing them to the user, you can pass them as a separate argument. You can use the same argument to override certain options depending on where the function is used.
def list_pets(%{} = args, opts \\ [], %User{} = current_user) do
flop_opts =
opts
|> Keyword.take([
:default_limit,
:default_pagination_type,
:pagination_types
])
|> Keyword.put(:for, Pet)
Pet
|> scope(current_user)
|> apply_filters(opts)
|> Flop.validate_and_run(flop, flop_opts)
end
defp scope(q, %User{role: :admin}), do: q
defp scope(q, %User{id: user_id}), do: where(q, user_id: ^user_id)
defp apply_filters(q, opts) do
Enum.reduce(opts, q, fn
{:last_health_check, dt}, q -> where(q, [p], p.last_health_check < ^dt)
{:reminder_service, bool}, q -> where(q, [p], p.reminder_service == ^bool)
_, q -> q
end)
end
Flop Phoenix is a companion library that defines view helpers for use in Phoenix templates.