如何将数据库记录存储到Rails的哈希红宝石中

Question

I'm using mysql database. Now I want to retrieve data from my database: value and time, for plotting graph. my db store up to 4000 data,and I need plot 1000 of them.

First method come to my mind is:

points=Hash.new
Records.all.each do |record|
  points[record.time.to_s]=record.value.to_s
end

then cut the first 1000 records.

But this way will be very inefficient and time consuming,It will cause my web load long.

I feel there must be a efficient way of doing this? convert first 1000 database records's attributes into hash? or convert to array pairs also ok for me,as long as data pair can plot.

thanks!

Answer 1

data = Record.limit(1000)          # Load no more than a 1000 entries
             .pluck(:time, :value) # Pick the field values into sub-arrays
                                   # it will also `SELECT` only these two
# At this point you have [[time1, value1], [time2, value2]]
# good already, but we can go further:
             .to_h # Ruby 2.1+ only! I hope you're up-to-date!
# Now it is {time1 => value1, time2 => value2}

Answer 2

您可以使用limit ：

points = Record.limit(1000).map { |r| { r.time => r.value } }