ruby on rails - 'Where-in' query in postgresql for two different queries showing same result -

i have active record assosciation relation follows.

@tasks =  #<activerecord::associationrelation [#<task id: 3130, title: "commit @ least 1 small win today", content: "when check-in on app lets me acknowledge m...",created_at: "2016-01-13 01:36:15", updated_at: "2016-01-13 04:47:57", state: "active", #<task id: 3131, title: "purposefully walk 3 minutes ", content: "more ordinary day, choose 5 minutes ...", created_at: "2016-01-13 04:52:32", updated_at: "2016-01-13 04:56:22", state: "active", #<task id: 3132, title: "1km walk or run sunday", content: "i pick direction, start 10 minute warm up,...", created_at: "2016-01-13 04:56:05", updated_at: "2016-01-13 04:56:05", state: "active",#<task id: 3249, title: "1km walk or run wednesday", content: "i pick direction, start 10 minute warm up,...", created_at: "2016-01-24 23:23:34", updated_at: "2016-01-24 23:23:34", state: "active"]>    @array = []  @tasks.each |task| if (condition)   @array << task.id end    @tasks = @tasks.where.not('tasks.id in (?)',@array) 

if non empty value in @array,
above condition working fine.

if @array = [] i,e empty array,
@tasks = @tasks.where.not('tasks.id in (?)',@array) not giving me correct result.

also, @tasks = @tasks.where('tasks.id in (?)',@array), condition removing 'not' giving same result when not present when array []

 @habits = @habits.where.not('habits.id in (?)',@id_s)  ====> output => []  @habits = @habits.where('habits.id in (?)',@id_s)  ====> output => []  both returning same optput if @id_s [] 

why these queries returning same value 2 different conditions?

if rails version date should switch hash notation, handles special cases empty arrays you:

@tasks = @tasks.where.not(id: @array)