sql - Ruby on Rails get records by highest price -

-

i have model rails model called orders has type_id, location, , price. each type can have multiple orders @ same location different prices. check below idea of table structure.

id | type_id | location_id | price ----------------------------------- 1  | 1       | 1           | 12 2  | 1       | 1           | 14 3  | 1       | 1           | 9 4  | 2       | 1           | 1 5  | 2       | 1           | 4 6  | 3       | 1           | 15 7  | 3       | 1           | 7

i wanting select records type_id using in example:

type_ids = "1,2,3" location_id = 1  order.find(:all, :conditions => ["location_id = ? , type_id in (?)", location_id, type_ids])

i want select record highest price each type in location, result set bring records id 2, 5 , 6.

i can not seem work out find query this, hope understand mean. if not ask can try , explain better.

cheers

eef

if want single highest-price conditions, use 

order.find(:first, :conditions => ["location_id = ? , type_id in (?)", location_id, type_ids], :order => 'price desc')

...because query order matching records highest lowest price, give first record (highest price).

if want highest-price item each type, you're breaking out of rails' query building , using find_by_sql get max(price) each instance of type_id (something select *, max(price) orders location_id = ? , type_id in (?) group type_id, i'd want run query few times against database refine it, myself).

unless number of type_ids large (e.g. in hundreds) might simpler run above query once each type , put results in 1 array; mysql query faster, particularly large numbers of type_ids, doing in rails enough unless you're determined max(price) query right.


Comments

Post a Comment

Popular posts from this blog

C#: Application without a window or taskbar item (background app) that can still use Console.WriteLine() -

-
i'm trying create application adheres following: no taskbar no console or form window can utilize console.writeline() . (i.e. if executes app command prompt write console.) the problem if create windows form (or wpf) application can have there no taskbar, console or window show up, console.writeline() nothing. if create console app, writes console, can't figure out how hide (and if did hide it, write command prompt window?)... how do this? just create standard console application. callers responsibility hide window caused program (from how run c# console application console hidden ): system.diagnostics.processstartinfo start = new system.diagnostics.processstartinfo(); start.filename = dir + @"\myprocesstostart.exe"; start.windowstyle = system.diagnostics.processwindowstyle.hidden;
Read more

c++ - Convert big endian to little endian when reading from a binary file -

-
this question has answer here: how convert between big-endian , little-endian values in c++? 28 answers i've been looking around how convert big-endian little-endians. didn't find solve problem. seem there's many way can conversion. anyway following code works ok in big-endian system. how should write conversion function work on little-endian system well? this homework, since systems @ school running big-endian system. it's got curious , wanted make work on home computer also #include <iostream> #include <fstream> using namespace std; int main() { ifstream file; file.open("file.bin", ios::in | ios::binary); if(!file) cerr << "not able read" << endl; else { cout << "opened" << endl; int i_var; double d_var; while(!file.eof()) {...
Read more

openssl - Load PKCS#8 binary key into Ruby -

-
i'm trying load particular private key encoded in binary der format ( pkcs#8 ) ruby. however, openssl::pkey won't recognize it. can make work doing console work , transforming pem so: openssl pkcs8 -inform der -in file.key -passin pass:xxxxxxxx >private_key.pem after this, key can correctly read. however, since whole process done in memory instead of writing , reading files. so question is: possible load private keys binary encoded der format ruby/openssl? thank time, fernando yes, can indirectly load pkcs#8 der-encoded private keys using ruby openssl. openssl::pkey::rsa.new handle pem-formatted pkcs#8, easy read binary der , convert pem-formatted string , load string. for example, these der-encoded private keys: $ openssl genrsa | openssl pkcs8 -topk8 -outform der \ -nocrypt -out pkcs8.key $ openssl genrsa | openssl pkcs8 -topk8 -outform der \ -v2 des3 -passout pass:secret -out pkcs8_des3.key you can this: require 'open...
Read more