I have a stream of data, which contains categories. I want to maintain a Category table which should contain every category I encounter exactly once.
I want to implement a id = Category.upsert(name), which should be atomic (of course), and - if possible - not use stored procedures on the DB side.
The upsert gem seems to do just that - I found it while googling to see if "upsert" is a thing.
How about this:
class Category < ActiveRecord::Base
...
class << self
def upsert(name)
transaction { self.find_or_create_by(name: name).id }
end
end
end
You will have to write an ActiveRecordExtension. Check this out.
The code will look something like this
module ActiveRecordExtension
extend ActiveSupport::Concern
def upsert(attributes)
begin
create(attributes)
rescue ActiveRecord::RecordNotUnique, PG::UniqueViolation => e
find_by_primary_key(attributes['primary_key']).
update(attributes)
end
end
end
ActiveRecord::Base.send(:include, ActiveRecordExtension)
Related
I'm trying to mimic ActiveRecord with a simple set of ruby objects for running raw sql queries. Below is a spike I've been experimenting with:
module Runable
def run
return self::Results.new
end
end
module Query
class Results
def initialize
#results = Object.find_by_sql()
end
def to_a
#code
end
end
end
module Scored
extend Runable
include Query
QUERY = 'a raw sql query string'
end
module Unseen
extend Runable
include Query
QUERY = 'a different raw sql query string'
end
What I want to be able to do is create simple Modules for each type of raw sql query I'm going to run, put them into a file like Scored or Unseen above and call .run on them to get back a results object. So like this:
Scored.run #=> #<Scored::Results:0x0000000000>
Unseen.run #=> #<Unseen::Results:0x0000000000>
but instead I get this...
Scored.run #=> #<Query::Results:0x0000000000>
Unseen.run #=> #<Query::Results:0x0000000000>
I've been doing ruby and rails for over a year but I'm just beginning to get into more advanced ruby usage. This is my first big step into using modules and mixins.
The issue, as far as I can tell, is that module class methods have self scoped to the module they're defined in. So I get Query::Results because the initialize method for Results is defined in the Query module. That make sense?
Thank you for the help!
Update 5/30 16:45
Basically, I want to wrap a handful of raw SQL statements into modules like this:
module ScoredUsers
include Queryable
QUERY="SELECT * FROM users ..."
end
and interact with the queries like this:
r = ScoredUsers.run #=> ScoredUsers::Results
r.ids
r.load_objects
REDIS.zadd user:5:cache, r.to_a
I want to keep everything in modules and classes, the ruby way (I think?) so when I want to create a new query object I can simple use the boilerplate module like Scored above.
The reason why you are getting such a results is that class Results is created just once. When the module is included new constant is created within including class (Scored::Results), but it is pointing to same memory space as constant Query::Results.
What you need is that you have to create a new class for each class this module is being included in. This is perfect opportunity to use included method:
module Query
def self.included(mod)
results = Class.new do
def initialize
#results = Object.find_by_sql()
end
def to_a
#code
end
end
mod.const_set('Results', results)
end
end
Now of course we are left with the question - do we really need to do this? This depends on how you are planning to use those classes.
I'm working on a project to recreate some of the functionality of ActiveRecord. Here's the portion that isn't working
module Associations
def belongs_to(name, params)
self.class.send(:define_method, :other_class) do |name, params|
(params[:class_name] || name.camelize).constantize
end
self.class.send(:define_method, :other_table_name) do |other_class|
other_class.table_name
end
.
.
.
o_c = other_class(name, params)
#puts this and other (working) values in a query
query = <<-SQL
...
SQL
#sends it off with db.execute(query)...
I'm building towards this testing file:
require 'all_files' #holds SQLClass & others
pets_db_file_name = File.expand_path(File.join(File.dirname(__FILE__), "pets.db"))
DBConnection.open(pets_db_file_name)
#class Person
#end
class Pet < SQLClass
set_table_name("pets")
set_attrs(:id, :name, :owner_id)
belongs_to :person, :class_name => "Person", :primary_key => :id, :foreign_key => :owner_id
end
class Person < SQLClass
set_table_name("people")
set_attrs(:id, :name)
has_many :pets, :foreign_key => :owner_id
end
.
.
.
Without any changes I received
.../active_support/inflector/methods.rb:230:in `block in constantize': uninitialized constant Person (NameError)
Just to make sure that it was an issue with the order of loading the classes in the file I began the file with the empty Person class, which, as predicted gave me
undefined method `table_name' for Person:Class (NoMethodError)
Since this is a learning project I don't want to change the test to make my code work (open all the classes, set all the tables/attributes then reopen them them for belongs_to. But, I'm stuck on how else to proceed.)
EDIT SQLClass:
class SQLClass < AssignmentClass
extend SearchMod
extend Associations
def self.set_table_name(table_name)
#table_name = table_name
end
def self.table_name
#table_name
end
#some more methods for finding rows, and creating new rows in existing tables
And the relevant part of AssignmentClass uses send on attr_accessor to give functionality to set_attrs and makes sure that before you initialize a new instance of a class all the names match what was set using set_attrs.
This highlights an important difference between dynamic, interpreted Ruby (et al) and static, compiled languages like Java/C#/C++. In Java, the compiler runs over all your source files, finds all the class/method definitions, and matches them up with usages. Ruby doesn't work like this -- a class "comes into existence" after executing its class block. Before that, the Ruby interpreter doesn't know anything about it.
In your test file, you define Pet first. Within the definition of Pet, you have belongs_to :person. belongs_to does :person.constantize, attempting to get the class object for Person. But Person doesn't exist yet! Its definition comes later in the test file.
There are a couple ways I can think that you could try to resolve this:
One would be to do what Rails does: define each class in its own file, and make the file names conform to some convention. Override constant_missing, and make it automatically load the file which defines the missing class. This will make load order problems resolve themselves automatically.
Another solution would be to make belongs_to lazy. Rather than looking up the Person class object immediately, it could just record the fact that there is an association between Pet and Person. When someone tries to call pet.person, use a missing_method hook to actually define the method. (Presumably, by that time all the class definitions will have been executed.)
Another way would be do something like:
define_method(belongs_to) do
belongs_to_class = belongs_to.constantize
self.class.send(:define_method, belongs_to) do
# put actual definition here
end
self.send(belongs_to)
end
This code is not tested, it's just to give you an idea! Though it's a pretty mind-bending idea, perhaps. Basically, you define a method which redefines itself the first time it is called. Just like using method_missing, this allows you to delay the class lookup until the first time the method is actually used.
If I can say one more thing: though you say you don't want to "overload" method_missing, I don't think that's as much of a problem as you think. It's just a matter of extracting code into helper methods to keep the definition of method_missing manageable. Maybe something like:
def method_missing(name,*a,&b)
if has_belongs_to_association?(name)
invoke_belongs_to_association(name,a,b)
elsif has_has_many_association?(name)
invoke_has_many_association(name,a,b)
# more...
else
super
end
end
Progress! Inspired by Alex D's suggestion to use method_missing to delay the creation I instead used define_methodto create a method for the name, like so:
define_method, :other_class) do |name, params|
(params[:class_name] || name.camelize).constantize
end
define_method(:other_table_name) do |other_class|
other_class.table_name
end
#etc
define_method(name) do #|params| turns out I didn't need to pass in `params` at all but:
#p "---#{params} (This is line 31: when testing this out I got the strangest error
#.rb:31:in `block in belongs_to': wrong number of arguments (0 for 1) (ArgumentError)
#if anyone can explain this I would be grateful.
#I had declared an #params class instance variable and a getter for it,
#but nothing that should make params require an argument
f_k = foreign_key(name, params)
p f_k
o_c = other_class(name, params)
o_t_n = other_table_name(o_c)
p_k = primary_key(params)
query = <<-SQL
SELECT *
FROM #{o_t_n}
WHERE #{p_k} = ?
SQL
row = DBConnection.execute(query, self.send(f_k))
o_c.parse_all(row)
end
I had the following function. It worked, but I don't like the way it looked.
# in user.rb
def awarded_requests
Request.joins('JOIN application ON application.request_id = request.id').where('accepted = true AND application.user_id = ?', self.id)
end
Then I refactored it to something that's clearly an improvement, but probably not simplest possible form:
def awarded_requests
Request.find(self.applications.accepted.map(&:request_id))
end
Can this be simplified further?
If you set up has many relationship, you can filter out those requests by merging a scope.
class User
has_many :applications
def awarded_requests
Request.joins(:applications).merge(applications.accepted)
end
end
Note that applications.accepted is not an array of records but a scope. This is how Active Record represents a part of SQL query internally, therefore it can smartly combine a few of them.
I want to be able to override certain methods in ActiveRecord::QueryMethods for educational and experimental reasons.
Example: User is an ActiveRecord class that includes modules that overwrite the QueryMethod "order":
User.where("last_logged_in_at < ?", 1.year.ago).order("my own kind of arguments here")
However, I can't seem to get things to work. What module should I override? Something in the ARel gem, AR::Relation, or AR::QueryMethods?
I think the answer is to track down where the existing Arel order is defined.
module ActiveRecord
module QueryMethods
def order(*args)
relation = clone
relation.order_values += args.flatten unless args.blank?
relation
end
end
end
A quick test in console verifies change this will work
module ActiveRecord::QueryMethods
def order(*args)
relation = clone
if args.first
puts "ordering in ascending id"
relation.order_values += ["id ASC"]
else
puts "ordering in descending id"
relation.order_values += ["id DESC"]
end
relation
end
end
So, you can do something like this.
But my suggestion would be to create a custom my_order which keeps the original order intact, but encapsulates the same logic.
But you can define this straight on active record
class ActiveRecord::Base
class << self
def my_order(*args)
self.order(*my logic for ordering*)
end
end
end
I am building a search with the keywords cached in a table. Before a user-inputted keyword is looked up in the table, it is normalized. For example, some punctuation like '-' is removed and the casing is standardized. The normalized keyword is then used to find fetch the search results.
I am currently handling the normalization in the controller with a before_filter. I was wondering if there was a way to do this in the model instead. Something conceptually like a "before_find" callback would work although that wouldn't make sense on for an instance level.
You should be using named scopes:
class Whatever < ActiveRecord::Base
named_scope :search, lambda {|*keywords|
{:conditions => {:keyword => normalize_keywords(keywords)}}}
def self.normalize_keywords(keywords)
# Work your magic here
end
end
Using named scopes will allow you to chain with other scopes, and is really the way to go using Rails 3.
You probably don't want to implement this by overriding find. Overriding something like find will probably be a headache down the line.
You could create a class method that does what you need however, something like:
class MyTable < ActiveRecord::Base
def self.find_using_dirty_keywords(*args)
#Cleanup input
#Call to actual find
end
end
If you really want to overload find you can do it this way:
As an example:
class MyTable < ActiveRecord::Base
def self.find(*args)
#work your magic here
super(args,you,want,to,pass)
end
end
For more info on subclassing checkout this link: Ruby Tips
much like the above, you can also use an alias_method_chain.
class YourModel < ActiveRecord::Base
class << self
def find_with_condition_cleansing(*args)
#modify your args
find_without_condition_cleansing(*args)
end
alias_method_chain :find, :condition_cleansing
end
end