Ecto creating unique index failed for Mysql/Mariadb

Question

I try to do the following migration:

defmodule Shopper.Repo.Migrations.MakeNameUniqueShopper do
  use Ecto.Migration

  def change do
    create unique_index :shoppers, [:name]
  end
end

Also tried create unique_index :shoppers, [:name], name: :name_unique, create unique_index :shoppers, [:name], name: "name_unique", and create index(:shoppers, [:name], unique: true)

But they failed with similar error:

[info]  == Running Shopper.Repo.Migrations.MakeNameUniqueShopper.change/0 forward

[info]  create index shoppers_name_index
** (Mariaex.Error) (1071): Specified key was too long; max key length is 767 bytes
    (ecto) lib/ecto/adapters/sql.ex:172: Ecto.Adapters.SQL.query!/5
    (elixir) lib/enum.ex:1261: Enum."-reduce/3-lists^foldl/2-0-"/3
...
...

Any help would be very appreciated, to help me with the error.

Note: I'm using ecto 1.02

Following is the first migration created with mix phoenix.gen.model

defmodule Shopper.Repo.Migrations.CreateV1.Shopper do
  use Ecto.Migration

  def change do
    create table(:shoppers) do
      add :name, :string
      add :oauth_token, :string

      timestamps
    end
  end
end

Info: the name field is utf8mb4, specified by my schema

Update: I know the solution is to reduce the name field length, but how to make it work with phoenix model and migration? As it expects a string?

Answer 1

Thanks to José Valim for helping me through his answer, though this answer is the exact solution for my problem.

Create a new ecto migration script with the following code:

defmodule Shopper.Repo.Migrations.MakeNameUniqueShopper do
  use Ecto.Migration

  def change do
    alter table(:shoppers) do
      modify :name, :string, size: 100
    end

    create unique_index :shoppers, [:name], name: :shopper_name_unique
  end
end