Ecto.Adapters.SQL.Connection.to_constraints

You're seeing just the callback to_constraints, go back to Ecto.Adapters.SQL.Connection module for more information.
Link to this callback

to_constraints(exception, options)

View Source

Specs

to_constraints(exception :: Exception.t(), options :: Keyword.t()) ::
  Keyword.t()

Receives the exception returned by query/4.

The constraints are in the keyword list and must return the constraint type, like :unique, and the constraint name as a string, for example:

[unique: "posts_title_index"]

Must return an empty list if the error does not come from any constraint.