Ecto custom SQL function

augnustin

Are there some Ecto gurus here?

I have this SQL function which works amazingly well (using Postgres 11.6)

CREATE EXTENSION IF NOT EXISTS "unaccent";

CREATE OR REPLACE FUNCTION slugify("value" TEXT)
RETURNS TEXT AS $$
  -- removes accents (diacritic signs) from a given string --
  WITH "unaccented" AS (
    SELECT unaccent("value") AS "value"
  ),
  -- lowercases the string
  "lowercase" AS (
    SELECT lower("value") AS "value"
    FROM "unaccented"
  ),
  -- remove single and double quotes
  "removed_quotes" AS (
    SELECT regexp_replace("value", '[''"]+', '', 'gi') AS "value"
    FROM "lowercase"
  ),
  -- replaces anything that's not a letter, number, hyphen('-'), or underscore('_') with a hyphen('-')
  "hyphenated" AS (
    SELECT regexp_replace("value", '[^a-z0-9\\-_]+', '-', 'gi') AS "value"
    FROM "removed_quotes"
  ),
  -- trims hyphens('-') if they exist on the head or tail of the string
  "trimmed" AS (
    SELECT regexp_replace(regexp_replace("value", '\-+$', ''), '^\-', '') AS "value"
    FROM "hyphenated"
  )
  SELECT "value" FROM "trimmed";
$$ LANGUAGE SQL STRICT IMMUTABLE;

select * from user u
where slugify(u.administrative) = 'ile-de-france';

I have no idea how I could insert it in a ecto query, like:

    User
      |> where(slugify(:administrative, ^administrative))
      |> order_by([f], f.city)
      |> Repo.all()

Can someone help me with that? My searches for “Ecto custom SQL function” did not produce any result.

Using 100% custom SQL query would be a pain because I need to chain it with other query criteria afterwards.

7 comments

#ecto #ecto_sql

0 2899 7

2020-04-29 11:49:41 UTC

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hauleth

Use fragment or check out my ecto_function (which is fancy way to use fragment).

Post #1

augnustin

Sounds promising @hauleth but where should I put the SQL function definition?

Your examples in the readme.md only use pre-defined SQL functions…

Thanks

Post #2

hauleth

From the viewpoint of Ecto/EctoFunction there is no difference between these two, so in you case it should work like that:

defqueryfunc slugify(value)

from u un user,
  where: slugify(u.administrative) == ^administrative

Post #3

augnustin

Yes, but I do need to tell postgres about this function definition. Any idiomatic way to do that with Ecto (or postgrex)?

Post #4

hauleth

You need to create that function in migration. You do not “tell” Postgres about function each time you want to use it.

Post #5

augnustin

You rock my world @hauleth

Here’s my migration:

defmodule Vae.Repo.Migrations.AddSlugifySQLFunction do
  use Ecto.Migration

  def change do
    Ecto.Adapters.SQL.query!(
      MyApp.Repo, """

CREATE EXTENSION IF NOT EXISTS "unaccent";

    """ )

    Ecto.Adapters.SQL.query!(
      MyApp.Repo, """

CREATE OR REPLACE FUNCTION slugify("value" TEXT)
RETURNS TEXT AS $$
  -- removes accents (diacritic signs) from a given string --
  WITH "unaccented" AS (
    SELECT unaccent("value") AS "value"
  ),
  -- lowercases the string
  "lowercase" AS (
    SELECT lower("value") AS "value"
    FROM "unaccented"
  ),
  -- remove single and double quotes
  "removed_quotes" AS (
    SELECT regexp_replace("value", '[''"]+', '', 'gi') AS "value"
    FROM "lowercase"
  ),
  -- replaces anything that's not a letter, number, hyphen('-'), or underscore('_') with a hyphen('-')
  "hyphenated" AS (
    SELECT regexp_replace("value", '[^a-z0-9\\-_]+', '-', 'gi') AS "value"
    FROM "removed_quotes"
  ),
  -- trims hyphens('-') if they exist on the head or tail of the string
  "trimmed" AS (
    SELECT regexp_replace(regexp_replace("value", '\-+$', ''), '^\-', '') AS "value"
    FROM "hyphenated"
  )
  SELECT "value" FROM "trimmed";
$$ LANGUAGE SQL STRICT IMMUTABLE;

    """ )
  end
end

Post #6

hauleth

You do not need to use Ecto,Adapters.SQL.query!/2 in the migrations. More - it is dangerous to do so (for example what if you will have multiple repos?). Instead use execute/{1,2}.

Post #7

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