How do I run a ruby function inside an ActiveRecord query?











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City.all.sample{rand(1..3)} I want the random function to generate the sample count. This always returns one record.






ruby activerecord ruby-on-rails-5







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  • @iGian couple of hundred times. Less than a thousand.
    – tambakoo
    13 hours ago






  • 1




    [1, 2, 3, 4, 5, 6, 7].sample(rand(1..3))
    – iGian
    13 hours ago










  • @iGian that was super simple! Thanks.
    – tambakoo
    13 hours ago










  • sample is not an active record query, though.
    – Sergio Tulentsev
    13 hours ago






  • 1




    @tambakoo: that it is, but you are not passing your logic to it. It runs unaltered. And then sample acts on the results. And in general, you can't "pass a ruby function to be used in a query". That's the whole point of the databases: to filter/sort/return data with maximum efficiency.
    – Sergio Tulentsev
    13 hours ago

















up vote
0
down vote

favorite












City.all.sample{rand(1..3)} I want the random function to generate the sample count. This always returns one record.






ruby activerecord ruby-on-rails-5







share|improve this question






















  • @iGian couple of hundred times. Less than a thousand.
    – tambakoo
    13 hours ago






  • 1




    [1, 2, 3, 4, 5, 6, 7].sample(rand(1..3))
    – iGian
    13 hours ago










  • @iGian that was super simple! Thanks.
    – tambakoo
    13 hours ago










  • sample is not an active record query, though.
    – Sergio Tulentsev
    13 hours ago






  • 1




    @tambakoo: that it is, but you are not passing your logic to it. It runs unaltered. And then sample acts on the results. And in general, you can't "pass a ruby function to be used in a query". That's the whole point of the databases: to filter/sort/return data with maximum efficiency.
    – Sergio Tulentsev
    13 hours ago















up vote
0
down vote

favorite









up vote
0
down vote

favorite











City.all.sample{rand(1..3)} I want the random function to generate the sample count. This always returns one record.






ruby activerecord ruby-on-rails-5







share|improve this question













City.all.sample{rand(1..3)} I want the random function to generate the sample count. This always returns one record.






ruby activerecord ruby-on-rails-5




ruby activerecord ruby-on-rails-5






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 14 hours ago









tambakoo

5510




5510












  • @iGian couple of hundred times. Less than a thousand.
    – tambakoo
    13 hours ago






  • 1




    [1, 2, 3, 4, 5, 6, 7].sample(rand(1..3))
    – iGian
    13 hours ago










  • @iGian that was super simple! Thanks.
    – tambakoo
    13 hours ago










  • sample is not an active record query, though.
    – Sergio Tulentsev
    13 hours ago






  • 1




    @tambakoo: that it is, but you are not passing your logic to it. It runs unaltered. And then sample acts on the results. And in general, you can't "pass a ruby function to be used in a query". That's the whole point of the databases: to filter/sort/return data with maximum efficiency.
    – Sergio Tulentsev
    13 hours ago




















  • @iGian couple of hundred times. Less than a thousand.
    – tambakoo
    13 hours ago






  • 1




    [1, 2, 3, 4, 5, 6, 7].sample(rand(1..3))
    – iGian
    13 hours ago










  • @iGian that was super simple! Thanks.
    – tambakoo
    13 hours ago










  • sample is not an active record query, though.
    – Sergio Tulentsev
    13 hours ago






  • 1




    @tambakoo: that it is, but you are not passing your logic to it. It runs unaltered. And then sample acts on the results. And in general, you can't "pass a ruby function to be used in a query". That's the whole point of the databases: to filter/sort/return data with maximum efficiency.
    – Sergio Tulentsev
    13 hours ago


















@iGian couple of hundred times. Less than a thousand.
– tambakoo
13 hours ago




@iGian couple of hundred times. Less than a thousand.
– tambakoo
13 hours ago




1




1




[1, 2, 3, 4, 5, 6, 7].sample(rand(1..3))
– iGian
13 hours ago




[1, 2, 3, 4, 5, 6, 7].sample(rand(1..3))
– iGian
13 hours ago












@iGian that was super simple! Thanks.
– tambakoo
13 hours ago




@iGian that was super simple! Thanks.
– tambakoo
13 hours ago












sample is not an active record query, though.
– Sergio Tulentsev
13 hours ago




sample is not an active record query, though.
– Sergio Tulentsev
13 hours ago




1




1




@tambakoo: that it is, but you are not passing your logic to it. It runs unaltered. And then sample acts on the results. And in general, you can't "pass a ruby function to be used in a query". That's the whole point of the databases: to filter/sort/return data with maximum efficiency.
– Sergio Tulentsev
13 hours ago






@tambakoo: that it is, but you are not passing your logic to it. It runs unaltered. And then sample acts on the results. And in general, you can't "pass a ruby function to be used in a query". That's the whole point of the databases: to filter/sort/return data with maximum efficiency.
– Sergio Tulentsev
13 hours ago














1 Answer
1






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oldest

votes

















up vote
0
down vote













I'd suggest this way, to avoid retrieving all records:



n.times.map.with_object() { |_, a| a << City.find(City.ids.sample) }


It returns an array of records.



Of course, n can be a random integer.






share|improve this answer





















  • Why not City.order('RAND()').limit(rand(1..3))? (RAND(), RANDOM()) depending the DB.
    – Sebastian Palma
    13 hours ago










  • @SebastianPalma: terrible performance for larger tables.
    – Sergio Tulentsev
    13 hours ago










  • You could also City.find(City.ids.sample(n)) to reduce the number of queries and get a unique set of cities but you'd still be pull all the ids out of the cities table to do the sampling in Ruby and you'd still have an array. City.where(id: City.ids.sample(n)) would give you a relation but, again, you're still pulling all the ids out of the database.
    – mu is too short
    5 hours ago











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1 Answer
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oldest

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1 Answer
1






active

oldest

votes









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oldest

votes






active

oldest

votes








up vote
0
down vote













I'd suggest this way, to avoid retrieving all records:



n.times.map.with_object() { |_, a| a << City.find(City.ids.sample) }


It returns an array of records.



Of course, n can be a random integer.






share|improve this answer





















  • Why not City.order('RAND()').limit(rand(1..3))? (RAND(), RANDOM()) depending the DB.
    – Sebastian Palma
    13 hours ago










  • @SebastianPalma: terrible performance for larger tables.
    – Sergio Tulentsev
    13 hours ago










  • You could also City.find(City.ids.sample(n)) to reduce the number of queries and get a unique set of cities but you'd still be pull all the ids out of the cities table to do the sampling in Ruby and you'd still have an array. City.where(id: City.ids.sample(n)) would give you a relation but, again, you're still pulling all the ids out of the database.
    – mu is too short
    5 hours ago















up vote
0
down vote













I'd suggest this way, to avoid retrieving all records:



n.times.map.with_object() { |_, a| a << City.find(City.ids.sample) }


It returns an array of records.



Of course, n can be a random integer.






share|improve this answer





















  • Why not City.order('RAND()').limit(rand(1..3))? (RAND(), RANDOM()) depending the DB.
    – Sebastian Palma
    13 hours ago










  • @SebastianPalma: terrible performance for larger tables.
    – Sergio Tulentsev
    13 hours ago










  • You could also City.find(City.ids.sample(n)) to reduce the number of queries and get a unique set of cities but you'd still be pull all the ids out of the cities table to do the sampling in Ruby and you'd still have an array. City.where(id: City.ids.sample(n)) would give you a relation but, again, you're still pulling all the ids out of the database.
    – mu is too short
    5 hours ago













up vote
0
down vote










up vote
0
down vote









I'd suggest this way, to avoid retrieving all records:



n.times.map.with_object() { |_, a| a << City.find(City.ids.sample) }


It returns an array of records.



Of course, n can be a random integer.






share|improve this answer












I'd suggest this way, to avoid retrieving all records:



n.times.map.with_object() { |_, a| a << City.find(City.ids.sample) }


It returns an array of records.



Of course, n can be a random integer.







share|improve this answer












share|improve this answer



share|improve this answer










answered 13 hours ago









iGian

2,3842620




2,3842620












  • Why not City.order('RAND()').limit(rand(1..3))? (RAND(), RANDOM()) depending the DB.
    – Sebastian Palma
    13 hours ago










  • @SebastianPalma: terrible performance for larger tables.
    – Sergio Tulentsev
    13 hours ago










  • You could also City.find(City.ids.sample(n)) to reduce the number of queries and get a unique set of cities but you'd still be pull all the ids out of the cities table to do the sampling in Ruby and you'd still have an array. City.where(id: City.ids.sample(n)) would give you a relation but, again, you're still pulling all the ids out of the database.
    – mu is too short
    5 hours ago


















  • Why not City.order('RAND()').limit(rand(1..3))? (RAND(), RANDOM()) depending the DB.
    – Sebastian Palma
    13 hours ago










  • @SebastianPalma: terrible performance for larger tables.
    – Sergio Tulentsev
    13 hours ago










  • You could also City.find(City.ids.sample(n)) to reduce the number of queries and get a unique set of cities but you'd still be pull all the ids out of the cities table to do the sampling in Ruby and you'd still have an array. City.where(id: City.ids.sample(n)) would give you a relation but, again, you're still pulling all the ids out of the database.
    – mu is too short
    5 hours ago
















Why not City.order('RAND()').limit(rand(1..3))? (RAND(), RANDOM()) depending the DB.
– Sebastian Palma
13 hours ago




Why not City.order('RAND()').limit(rand(1..3))? (RAND(), RANDOM()) depending the DB.
– Sebastian Palma
13 hours ago












@SebastianPalma: terrible performance for larger tables.
– Sergio Tulentsev
13 hours ago




@SebastianPalma: terrible performance for larger tables.
– Sergio Tulentsev
13 hours ago












You could also City.find(City.ids.sample(n)) to reduce the number of queries and get a unique set of cities but you'd still be pull all the ids out of the cities table to do the sampling in Ruby and you'd still have an array. City.where(id: City.ids.sample(n)) would give you a relation but, again, you're still pulling all the ids out of the database.
– mu is too short
5 hours ago




You could also City.find(City.ids.sample(n)) to reduce the number of queries and get a unique set of cities but you'd still be pull all the ids out of the cities table to do the sampling in Ruby and you'd still have an array. City.where(id: City.ids.sample(n)) would give you a relation but, again, you're still pulling all the ids out of the database.
– mu is too short
5 hours ago


















 

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