CODEWITHSUNDEEP
ruby-on-railsruby
user2950593
user2950593

Reputation: 9617

Ruby count number of queries to database?

There is something I don't fully understand. Look at this example which makes n calls (or queries) to database where n is number of customers.

@reports = Report.where(:car => car)

for customer in customers
  report = @reports.where(:city => customer.city, :age=> customer.age)
end

This one below just call the database once, right?

@reports = Report.where(:car => car).where( :city => customers.map(&:city), :age => customers.map(&:age))

for customer in customers
  report = @reports.detect(:city => customer.city, :age=> customer.age)
end

Upvotes: 0

Views: 279

Answers (1)

Bengineer
Bengineer

Reputation: 7742

Yes, the second example just makes on call to the database.

When you do @reports= Report.where(:car => car).where( :city => customers.map(&:city), :age => customers.map(&:age)) you are loading all those records into the @reports variable.

So at the detect part it doesn't need to call the database, since the records are already there.

Upvotes: 1

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