Steps to reproduce

1. Create a new project and configure it with a PostgreSQL-database
2. $rails g model posts title body:text uuid:uuid date_column:datetime
3. Do the following in rails console:

      a = Post.create()
      b_uuid=SecureRandom.uuid
      b = Post.create(uuid: b_uuid)
      Post.find_by(uuid: b_uuid)
      # returns b OK
      another_random_uuid=SecureRandom.uuid
      Post.find_by(uuid: another_random_uuid)
      # returns nil OK
      Post.find_by(uuid: "not a uuid")

Expected behavior

I'd think that the last call should return nil or raise an exception.

Actual behavior

The last call returns Post a, a Post with a uuid that is nil.

Compareable behavior

Update: I wanted to compare it with Post.where(id:"a"), which returns nil, instead of c; but actually it searches for 0, which might lead to an unexpected find of a Post with id 0, but this case has been purely hypothetical for me; as ids typically start at 1 (and is kind of expected, since "a".to_i also returns 0 in plain ruby). Searching for an invalid date in e.g. where(date_column: "a"), however, used to (v5.1.5) return PG::InvalidDatetimeFormat but also silently continues with a search for nil. Below a table with some scenario's compared.

Related

Old issue, from long time ago, that actually settled on the 5.1.x behaviour: #11902, raising an exception.

System configuration

Rails version: 5.2.1

Ruby version: 2.4.1

(Was still working in 5.1.5/6)

update: Initially I thought that this was a Postgres only issue; but see the table above; unexpected things are happening with SQLite as well (not tested other database backends)