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Creating a unique constraint on two columns together in Ecto

How do you create a unique index on two columns in Ecto, which would correspond to this:

CREATE TABLE someTable (
    col1 int NOT NULL,
    col2 int NOT NULL,
    primary key (col1, col2)
)

?

Solution

  • A Little follow up on Patrick's answer

    Using only create unique_index on your model will ultimately throw an exception instead of giving you an error.

    To get an error add a constraint on your changeset but as a paremeter you can give the index name created by unique_index.

    So in your migration file : 

    create unique_index(:your_table, [:col1, :col2], name: :your_index_name)

    Then in your changeset :

    def changeset(model, param \\ :empty) do
  model
  |> cast(params, @required_fields, @optional_fields)
  |> unique_constraint(:name_your_constraint, name: :your_index_name)
end