Check out example codes for "arel_table rails". It will help you in understanding the concepts better.

Code Example 1

Address.where( Address.arel_table[:created_at].lt( 5.days.ago ) ).to_sql
# SELECT "addresses".* FROM "addresses"  WHERE ("addresses"."created_at" < '2016-12-13 03:31:23.911914')

Code Example 2

veg = Arel::Table.new(:vegetables)
query = veg[:created_at].gteq( 5.days.ago ).and(
  veg[:color].eq("green").or(
    veg[:gardener].eq("Susan")
  )
)
query.to_sql
#  "vegetables"."created_at" >= '2016-12-13 03:54:28.575342'
#    AND ("vegetables"."color" = 'green' OR "vegetables"."gardener" = 'Susan')
Vegetable.where( query )

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