TIL, 2017-07-06, Uniqueness Index

Ruby: I’m not that really excited about the safe navigation operator (&.), but it does make sense when you’re iterating over an update hash. Or just safe merge before the edit operation?
described_class.connection.index_exists?(:match_participants, [:match_id, :participant_id], unique: true) to check if an index exists.
Factory girl sequence to get around unique index.
Mass update at the same time, with different attributes per row–there’s no easy way to do this in Rails without resorting to 1 query per row, or else you have to do it by SQL.
Postgres DEFERRABLE uniqueness constraints only work on SQL.
Viewing database constraints in PostgreSQL: pg_catalog, pg_constraint or pg_catalog, pg_indexes.
RSpec: Recheck expect and allow: expect also sort of does the allow thing already, so.
make_database_queries(matching: /UPDATE/, count: 2) is a thing.
Ruby 2.4.0–10-15% more extra speed in Rails than 2.3.x. Reference