Hi, fellows!
Sometimes we need to get a random record from some table. The common way to get it is to use Array#sample method on a relation. Or, if your table is quiet large, you can use one of the ways your DB provides to do such thing. It could be MyModel.order(‘RAND()’).limit(1)
``
if you use MySQL, or
MyModel.order(‘RANDOM()’).limit(1)
``
if you use Postgresql.
This way is much more fast than using #sample method, even if your table is less then 1000 rows. But it has two downsides.
First, this code is now database-dependent. So if your code will some day migrate on an another DB, you will have to change it.
Second, it is not obvious for some rails novices, that doing MyModel.all.sample you actually use Array#sample method, that loads all relation collection in memory. If rails tend to be easy-to-start and clear for developer, it should not act this way.
So, my suggestion is to implement #sample method somewhere in ActiveRecord so that it will generate database query to get random row. There are functions to do it in all common DB distributions (MySQL, Postgresql, MS SQL, IBM DB2, Oracle). The usage could look like this:
MyModel.sample # returns one random record MyModel.sample(10) # returns 10 random records MyModel.all.sample # works identical to the first two examples; and this is not the Array#sample method. MyModel.some_scope.sample # returns one random record from a scope
``
and so on.
I think the performance benefit from such enhancement is quite obvious, but anyway, here is a benchmark for a Postgres table with 180 000 rows. 2.1.5 (main):0 > Benchmark.bm do |x|
2.1.5 (main):0 * x.report(‘sample’) { LessonVersion.all.sample }
2.1.5 (main):0 * x.report(‘RANDOM()’) { LessonVersion.order(‘RANDOM()’).limit(1) }
2.1.5 (main):0 * end
user system total real
sample 9.810000 8.690000 18.500000 ( 29.282437)
RANDOM() 0.000000 0.000000 0.000000 (0.000187)
=> [
[0] #<Benchmark::Tms:0x007fe7c699c568 @label=“sample”, @real=29.282437, @cstime=0.0, @cutime=0.0, @stime=8.69, @utime=9.81, @total=18.5>,
[1] #<Benchmark::Tms:0x007fe7c69a4420 @label=“RANDOM()”, @real=0.000187, @cstime=0.0, @cutime=0.0, @stime=0.0, @utime=0.0, @total=0.0>
]
``
I’ve already set up rails-dev-box on my laptop and cloned rails repository, but there is a CONTRIBUTING.md file, that recommends to get positive feedback before writing code. So, here is my proposal. I think I can write it myself, but ofcourse implementation suggestions are very welcome. Especially since I’m not very comfortible with ActiveRecord sources yet.
