UPDATE. Check these benchmarks to test it for yourself.
Should I store the collection of objects in a variable of some service like this:
ConfigService{
private def countries = Country.findAllBySomeCondition()
public def countries(){
return countries
}
}
or use:
ConfigService{
public def countries(){
return Country.findAllBySomeCondition()
}
}
If the collection will be used often only for read.
Depends. In your first example, the value is cached, which may be a little more efficient, but if at some point more Countries are added, they may not show up on your service call. However, if you call .countries() often with your second example, you may incur some performance hits.
The best option would probably be to get some benchmarks as to how long the queries take, and decide whether it's best to try to cache the value yourself, or to ensure that it's always up-to-date. My suggestion would be to stick with the second example, as Hibernate handles some caching for you already, and chances are the list is not big enough to significantly hinder your app.
#GrailsGuy's answer is spot on and I'm gave him a +1. To provide you with some other options you could:
1) If your list of Countries doesn't change you could put them in an enum and avoid the DB all together.
2) If you give the user the ability to add/remove/edit Countries then you could cache the list like you are in example 1 but then when the user add/remove/edits a country you can force reload the list.
ConfigService{
private def countries
public def countries(){
if(countries == null) {
countries = Country.findAllBySomeCondition()
}
return countries
}
}
CountryService {
def configService
def addCountry() {
//Do add country stuff
configService.countries = null
}
}
This way you can cache the countries until they get updated. Like #GrailsGuy said though Hibernate will do this to some extent for you.
Related
I'm trying to learn Grails but am still pretty much on beginner level.
I made a tiny application, where you can basically add events, and people can write reviews about them and rate them.
So I have an eventController and reviewController. The rating is just an Integer in a review. But now I want to show an overall rating for an event. So the events rating should be the average value of the corresponding ratings value.
This is my event domain code where the rating is initially set, I left out the constraints and toString:
class Event {
Double dRating = 2
static hasMany = [ratings:Rating]
}
The controller is simply:
class EventController {
def scaffold = Event
}
The rating domain file:
class Rating {
String comment
java.util.Date date = new java.util.Date()
Integer rating
Event event
}
and the Rating Controller is:
class RatingController {
def scaffold = Rating
}
Hope I didn't make mistakes, I had to translate variable names so they're understandable.
I'm guessing that where dRating is set, I could somehow add some calculation, but I don't even know how to access the values of the rating, and everything I try ends in lots of errors and having to restart the app again and again. I tried adding calculations in the controller, but there I don't know how to get the value into the database. So where do I actually put the logic, and how do I access the values?
If any other file is important, please tell me.
Hoping to get some hints on how to start doing this, I didn't think it would be this hard.
At first I would recommend start reading grails doc. Later from your question it is not much clear what you are asking a there could be several places or possibilities of setting up the value in domain field and persist it to database. I'm telling all of these which are known to me:
If it is generalised calculation that needs to be applied to your dRating field, then create a setter with standard bean naming convention and do this there. For example, you want to find percentage from say 1000 and then add it to dRating
class Event {
static hasMany = [ratings:Rating]
Double dRating
void setDRating(Double value){
this.dRating = value * 100/1000 // alternatively value /10
}
}
Do it in commandObject: If you don't want to put certain calculations and validation in domain then put these in command objects. See this. You can at any point of time assign values from command object to domain object by .properties binding mechanism. For example,
yourDomainObject.properties = yourcommandObjectObject.properties
Remember properties having same name would be binded.
Do it in service: You can do your calculations in service method, inject that service into your controller and call that method to perform calculations and even to persist to db as well. Remember services are by default transactional.
Hope it helps!
I'm trying to accelerate the performance of my app and wonder if there is a difference between accessing domain property value with instance.name and instance.getName()
If it is, which one is the best in terms of performance ?
Example
class User {
String name
}
User user = User.get(100);
//is it better this way
user.name
//or this way
user.getName()
Thank you
It doesn't matter for the usage you've provided, because user.name uses user.getName() behind scenes. So it's the same. If you want to access property directly you have to use # like this user.#name. See more here
But I don't think this is the way you can speed up your app.
It is very likely you will find a lot easier ways for improving performance of your code. Here are some ideas where to start if you like to improve performance.
A) Number of queries. Try to avoid the the N+1 problem. For example if one user hasMany [events: Event], code like user.events.each { access event.anyPropertyExceptId } will dispatch new queries for each event.
B) Efficiency of queries. Grails per default creates indexes for all gorm associations / other nested domains. However anything you use to search, filter etc. you need to do "manually" for example.
static mapping = {
anyDomainProperty index: 'customIndexName'
}
C) Only query for the data you are interested in, replace for example:
User.all.each { user ->
println user.events.size()
}
with
Event.withCriteria {
projections {
property('user')
countDistinct('id')
groupProperty('user')
}
}
D) If you really need to speed up your groovy code and your problem is rather a single request than general cpu usage, take a look at http://gpars.codehaus.org and http://grails.org/doc/2.3.8/guide/async.html and try to parallize work.
I doubt any performance issues in your application are related to how you are accessing your properties of your domain classes. In fact, if you profile/measure your application I'm sure you will see that is the case.
I'm newbie in Ruby but I have a lot of experience in other programming languages. I need to iterate over large amount of records (from db or any persistent storage). Storage engine allows me to retrieve records partially by ranges. In PHP I usually write custom iterator that loads range of records iterate over them and when need loads next part of records and forget about previous part. Some trade-off between script memory usage and count of request to storage. Something like this (copied from comments here):
class Database_Result_Iterator {
...
private $_db_resource = null;
private $_loaded = false;
private $_valid = false;
function rewind() {
if ($this->_db_resource) {
mysql_free($this->_db_resource);
$this->_db_resource = null;
}
$this->_loaded = false;
$this->_valid = false;
}
function valid() {
if ($this->_loaded) {
$this->load();
}
return $this->_valid;
}
private function load() {
$this->_db_resource = mysql_query(...);
$this->_loaded = true;
$this->next(); // Sets _valid
}
}
How such approach is transformed in Ruby? I.e. I have some class Voter and method get_votes that returns all votes belong to current voter object. It is possible to retrieve not an array with all votes but collection of votes with possibility to iterate over it. How should I implement it?
UPDATE
Please not consider ActiveRecord and RDBMS as only one possible storage. And what about Redis as storage and commands like LRANGE? I'm interested in common code pattern for solution such kind of problem in Ruby.
From the guides on Ruby on Rails:
User.all.each do |user|
NewsLetter.weekly_deliver(user)
end
Is very innefficient. You probably want to do most of the filtering in the database, to start with. ActiveRecord offers a method called find_each for this:
User.find_each(:batch_size => 5000) do |user|
NewsLetter.weekly_deliver(user)
end
The :batch_size parameter allows to fetch slices of data instead of getting the entire resultset. Extremely helpfull in most cases.
But, you probably don't want to operate on all records in the first place:
User.with_newsletter.each do |user|
NewsLetter.weekly_deliver(user)
end
Where with_newsletter is a so called scope.
I really don't see the point of this question.
AR is an API for querying RDBMS and that's how you do it in AR.
If you want to do redis you'll have to either write it yourself at the driver level or find a similar abstraction to AR for Redis... I think DataMapper had a redis adapter.
If there is a universal way to do this for any data store it is likely in DataMapper, but the basic pattern to follow when creating your own would be to look at how AR implements find_each/find_in_batches and do it for your store of choice.
It sounds like you want to use find_each (http://apidock.com/rails/ActiveRecord/Batches/ClassMethods/find_each). This lets you iterate through a large dataset by loading in a small number, iterating over them, then loading in another batch and so on.
User.find_each do |user|
user.do_some_stuff
end
will iterate through all users without loading a bajillion of them into memory at once.
I have two object, a room type and a reservation. Simplified they are:
class Room {
String description
int quantity
}
class Reservation {
String who
Room room
}
I want to query for all rooms along with the number of rooms available for each type. In SQL this does what I want:
select id, quantity, occupied, quantity-coalesce(occupied, 0) as available
from room left join(select room_id, count(room_id) as occupied from reservation)
on id = room_id;
I'm not getting anywhere trying to work out how to do this with HQL.
I'd appreciate any pointers since it seems like I'm missing something fairly fundamental in either HQL or GORM.
The problem here is your trying to represent fields that are not your domain classes like available and occupied. Trying to get HQL\GORM to do this can be a bit a little frustrating, but not impossible. I think you have a couple options here...
1.) Build your domain classes so that there easier to use. Maybe your Room needs to know about it's Reservations via a mapping table or, perhaps write what you want the code to look like and then adjust the design.
For example. Maybe you want your code to look like this...
RoomReservation.queryAllByRoomAndDateBetween(room, arrivalDate, departureDate);
Then you would implement it like this...
class RoomReservation{
...
def queryAllByRoomAndDateBetween(def room, Date arrivalDate, Date departureDate){
return RoomReservation.withCriteria {
eq('room', room)
and {
between('departureDate', arrivalDate, departureDate)
}
}
}
2.) My second thought is... It's okay to use the database for what it's good for. Sometimes using sql in you code is simply the most effective way to do something. Just do it in moderation and keep it centralized and unit tested. I don't suggest you use this approach because you query isn't that complex, but it is an option. I use stored procedures for things like 'dashboard view's' that query millions of objects for summary data.
class Room{
...
def queryReservations(){
def sql = new Sql(dataSoruce);
return sql.call("{call GetReservations(?)}", [this.id]) //<-- stored procedure.
}
}
I'm not sure how you can describe a left join with a subquery in HQL. INn any case you can easily execute raw SQL in grails too, if HQL is not expressive enough:
in your service, inject the dataSource and create a groovy.sql.Sql instance
def dataSource
[...]
def sql= new Sql(dataSource)
sql.eachRow("...."){row->
[...]
}
I know it's very annoying when people try to patronize you into their way of thinking when you ask a question, instead of answering your question or just shut up, but in my opinion, this query is sufficiently complex that I would create a concept for this number in my data structure, perhaps an Availability table associated to the Room, which would keep count not only of the quantity but also of the occupied value.
This is instead of computing it every time you need it.
Just my $.02 just ignore it if it annoys you.
Note I am referring to one request, and not several requests and sessions.
I have several components that require Doctrine user object, some are located in layout, others are located in templates. Sometimes I need that Doctrine user object in action. Currently I have added a function to sfUser class that loads that object from database, which means every time I call that function I make a call to db. I'd like to know where to store this object so that I can access it without having to query db every time I need it. Again, we're talking about a single request, not several requests or something that would require session.
Can I save it in sfContext somehow? Any other places so that it can be available everywhere?
You can store it in your model's Table class, because tables are always accessed as singletones.
class sfGuardUserTable extends PluginsfGuardUserTable
{
protected $specialUser = null;
public function getSpecialUser()
{
if (null === $this->specialUser)
{
$this->specialUser = $this->findOneById(1);
}
return $this->specialUser;
}
}
Now, you can use this in actions and components like this:
$u = sfGuardUserTable::getInstance()->getSpecialUser();
And you will always end up with one query.
you can configure Doctrine cache so that the result of this specific request is always cached. What if so good about it is that if you use, say, the APC backend, you will have it cached across requests. You also get query caching as a bonus (this is not result caching, read the link I provided carefully)!