I'm looking for the best Ruby way to accomplish this.
I have a Person that has_many Feeds through Subscriptions. So we can do things like Person.feeds, and it gets all the feeds a person is subscribed to.
Problem is, subscriptions are either authorized or deauthorized. What is the best way to make Person.feeds respect the Authorized status bit on the Subscription model?
So we can do something like Person.feeds.where(:status => authorized).
You can call this with a command like the following:
#person.feeds.joins(:subscription).where(subscriptions: { status: 'authorized' })
N.B. the joins takes the association's format, singular in this case, while where takes the table name, typically pluralised.
What this does in order is:
Loads the feeds belonging to a person
Joins these feeds to their subscription
Queries the subscriptions table to return only the feeds where the subscription is active
To refactor this, I'd include a couple of methods in the relevant models:
# feed.rb
scope :active, -> { joins(:subscription).where(subscriptions: { status: 'authorized' }) }
# person.rb
def active_feeds
feeds.active
end
Then, you can just call #person.active_feeds to get the results you want from anywhere in your code base.
(There's also the added bonus of Feed.active being available anywhere should you wish to display active feeds outside of a user's scope.)
Hope that helps - let me know if you've any questions.
Related
My situation is this: I have multiple components in my view that ultimately depend on the same data, but in some cases the view state is derived from the data. How do I make sure my whole view stays in sync when the underlying data changes? I'll illustrate with an example using everyone's favorite Star Wars API.
First, I show a list of all the films, with a query like this:
# ALL_FILMS
query {
allFilms {
id
title
releaseDate
}
}
Next, I want a separate component in the UI to highlight the most recent film. There's no query for that, so I'll implement it with a client-side resolver. The query would be:
# MOST_RECENT_FILM
query {
mostRecentFilm #client {
id
title
}
}
And the resolver:
function mostRecentFilmResolver(parent, variables, context) {
return context.client.query({ query: ALL_FILMS }).then(result => {
// Omitting the implementation here since it's not relevant
return deriveMostRecentFilm(result.data);
})
}
Now, where it gets interesting is when SWAPI gets around to adding The Last Jedi and The Rise of Skywalker to its film list. We can suppose I'm polling on the list so that it gets periodically refetched. That's great, now my list UI is up to date. But my "most recent film" UI isn't aware that anything has changed — it's still stuck in 2015 showing The Force Awakens, even though the user can clearly see there are newer films.
Maybe I'm spoiled; I come from the world of MobX where stuff like this Just Works™. But this doesn't feel like an uncommon problem. Is there a best practice in the realm of Apollo/GraphQL for keeping things in sync? Am I approaching this problem in entirely the wrong way?
A few ideas I've had:
My "most recent film" query could also poll periodically. But you don't want to poll too often; after all, Star Wars films only come out every other year or so. (Thanks, Disney!) And depending on how the polling intervals overlap there will still be a big window where things are out of sync.
Instead putting the deriveMostRecentFilm logic in a resolver, just put it in the component and share the ALL_FILMS query between components. That would work, but that's basically answering "How do I get this to work in Apollo?" with "Don't use Apollo."
Some complicated system of keeping track of the dependencies between queries and chaining refreshes based on that. (I'm not keen to invent this if I can avoid it!)
In Apollo observables are (in components) over queried values (cached data 'slots') but your mostRecentFilm is not an observable, is not based on cached values (they are cached) but on one time fired query result (updated on demand).
You're only missing an 'updating connection', f.e. like this:
# ALL_FILMS
query {
allFilms {
id
title
releaseDate
isMostRecentFilm #client
}
}
Use isMostRecentFilm local resolver to update mostRecentFilm value in cache.
Any query (useQuery) related to mostRecentFilm #client will be updated automatically. All without additional queries, polling etc. - Just Works? (not tested, it should work) ;)
I have a code section like the following:
users = User.all(:fname => "Paul")
This of course results in getting all users called "Paul". Now I only need some of the columns available for each user which leads to replacing the above line by something like this:
users = User.all(:name => "Paul", :fields => [:id, :fname, :lname, :email])
Until now everything works as expected. Unfortunately now I want to work with users but as soon as I use something like users.to_json, also the other columns available will be lazy-loaded even due the fact, that I don't need those. What's the correct or at least a good way to end up with users only containing the attributes for each user that I need?
An intermediate object like suggested in How to stop DataMapper from double query when limiting columns/fields? is not a very good option as I have a lot of places where would need to define at least twice which fields I need and also I would loose the speed improvement gained by loading only the needed data from the DB. In addition such an intermediate object also seems to be quite ugly to build when having multiple rows of the DB selected (=> multiple objects in a collection) instead of just one.
If you usually works with the collection using json I suggest overriding the as_json method in your model:
def as_json(options = nil)
# this example ignores the user's options
super({:only => [:fname]}.merge(options || {}))
end
You are able to find more detailed explanation here http://robots.thoughtbot.com/better-serialization-less-as-json
Is it possible to simply get the people you are following with just an id and full name? I do not need any of the additional data, it's a waste of bandwidth.
Currently the only solution I have is:
twitter_client = Twitter::Client.new
friend_ids = twitter_client.friend_ids['ids']
friends = twitter_client.users(friend_ids).map { |f| {:twitter_id => f.id, :name => f.name} }
is there anyway to just have users returned be an array of ids and full names? better way of doing it than the way depicted above? preferably a way to not filter on the client side.
The users method uses the users/lookup API call. As you can see on the page, the only param available is include_entities. The only other method which helps you find users has the same limitation. So you cannot download only the needed attributes.
The only other thing I'd like to say is that you could directly use the friends variable, I don't see any benefit of running the map on it.
There are two classes: User and Question
A user may have many questions, and it also contains a question_count
to record the the count of questions belong to him.
So, when I add a new question, I want update the question_count of the
user. At first, I do as:
question = Question(title='aaa', content='bbb')
Session.add(question)
Session.flush()
user = question.user
### user is not None
user.question_count += 1
Session.commit()
Everything goes well.
But I wan't to use event callback to do the same thing. As following:
from sqlalchemy.orm.interfaces import MapperExtension
class Callback(MapperExtension):
def after_insert(self, mapper, connection, instance):
user = instance.user
### user is None !!!
user.question_count += 1
class Question(Base):
__tablename__ = "questions"
__mapper_args__ = {'extension':Callback()}
....
Note in the "after_insert" method:
instance.user # -> Get None!!!
Why?
If I change that line to:
Session.query(User).filter_by(id=instance.user_id).one()
I can get the user successfully, But: the user can't be updated!
Look I have modified the user:
user.question_count += 1
But there is no 'update' sql printed in the console, and the
question_count are not updated.
I try to add Session.flush() or Session.commit() in the
after_insert() method, but both cause errors.
Is there any important thing I'm missing? Please help me, thank you
The author of sqlalchemy gave me an useful answer in a forum, I copy it here:
Additionally, a key concept of the
unit of work pattern is that it
organizes a full list of all
INSERT,UPDATE, and DELETE statements
which will be emitted, as well as the
order in which they are emitted,
before anything happens. When the
before_insert() and after_insert()
event hooks are called, this structure
has been determined, and cannot be
changed in any way. The
documentation for before_insert() and
before_update() mentions that the
flush plan cannot be affected at this
point - only individual attributes on
the object at hand, and those which
have not been inserted or updated yet,
can be affected here. Any scheme
which would like to change the flush
plan must use
SessionExtension.before_flush.
However, there are several ways of
accomplishing what you want here
without modifiying the flush plan.
The simplest is what I already
suggested. Use
MapperExtension.before_insert() on the
"User" class, and set
user.question_count =
len(user.questions). This assumes
that you are mutating the
user.questions collection, rather than
working with Question.user to
establish the relationship. If you
happened to be using a "dynamic"
relationship (which is not the case
here), you'd pull the history for
user.questions and count up what's
been appended and removed.
The next way, is to do pretty much
what you think you want here, that is
implement after_insert on Question,
but emit the UPDATE statement
yourself. That's why "connection" is
one of the arguments to the mapper
extension methods:
def after_insert(self, mapper, connection, instance):
connection.execute(users_table.update().\
values(question_count=users_table.c.question_count +1).\
where(users_table.c.id==instance.user_id))
I wouldn't prefer that approach since
it's quite wasteful for many new
Questions being added to a single
User. So yet another option, if
User.questions cannot be relied upon
and you'd like to avoid many ad-hoc
UPDATE statements, is to actually
affect the flush plan by using
SessionExtension.before_flush:
class
MySessionExtension(SessionExtension):
def before_flush(self, session, flush_context):
for obj in session.new:
if isinstance(obj, Question):
obj.user.question_count +=1
for obj in session.deleted:
if isinstance(obj, Question):
obj.user.question_count -= 1
To combine the "aggregate" approach of
the "before_flush" method with the
"emit the SQL yourself" approach of
the after_insert() method, you can
also use SessionExtension.after_flush,
to count everything up and emit a
single mass UPDATE statement with many
parameters. We're likely well in the
realm of overkill for this particular
situation, but I presented an example
of such a scheme at Pycon last year,
which you can see at
http://bitbucket.org/zzzeek/pycon2010/src/tip/chap5/sessionextension.py
.
And, as I tried, I found we should update the user.question_count in after_flush
user, being I assume a RelationshipProperty, is only populated after the flush (as it is only this point the ORM knows how to relate the two rows).
It looks like question_count is actually a derived property, being the number of Question rows for that user. If performance is not a concern, you could use a read-only property and let the mapper do the work:
#property
def question_count(self):
return len(self.questions)
Otherwise you're looking at implementing a trigger, either at the database-level or in python (which modifies the flush plan so is more complicated).
So, I'm not quite sure how I should structure this in CakePHP to work correctly in the proper MVC form.
Let's, for argument sake, say I have the following data structure which are related in various ways:
Team
Task
Equipment
This is generally how sites are and is quite easy to structure and make in Cake. For example, I would have the a model, controller and view for each item set.
My problem (and I'm sure countless others have had it and already solved it) is that I have a level above the item sets. So, for example:
Department
Team
Task
Equipment
Department
Team
Task
Equipment
Department
Team
Task
Equipment
In my site, I need the ability for someone to view the site at an individual group level as well as move to view it all together (ie, ignore the groups).
So, I have models, views and controls for Depart, Team, Task and Equipment.
How do I structure my site so that from the Department view, someone can select a Department then move around the site to the different views for Team/Task/Equipment showing only those that belong to that particular Department.
In this same format, is there a way to also move around ignoring the department associations?
Hopefully the following example URLs clarifies anything that was unclear:
// View items while disregarding which group-set record they belong to
http://www.example.com/Team/action/id
http://www.example.com/Task/action/id
http://www.example.com/Equipment/action/id
http://www.example.com/Departments
// View items as if only those associated with the selected group-set record exist
http://www.example.com/Department/HR/Team/action/id
http://www.example.com/Department/HR/Task/action/id
http://www.example.com/Department/HR/Equipment/action/id
Can I get the controllers to function in this manner? Is there someone to read so I can figure this out?
Thanks to those that read all this :)
I think I know what you're trying to do. Correct me if I'm wrong:
I built a project manager for myself in which I wanted the URLs to be more logical, so instead of using something like
http://domain.com/project/milestones/add/MyProjectName I could use
http://domain.com/project/MyProjectName/milestones/add
I added a custom route to the end (!important) of my routes so that it catches anything that's not already a route and treats it as a "variable route".
Router::connect('/project/:project/:controller/:action/*', array(), array('project' => '[a-zA-Z0-9\-]+'));
Whatever route you put means that you can't already (or ever) have a controller by that name, for that reason I consider it a good practice to use a singular word instead of a plural. (I have a Projects Controller, so I use "project" to avoid conflicting with it.)
Now, to access the :project parameter anywhere in my app, I use this function in my AppController:
function __currentProject(){
// Finding the current Project's Info
if(isset($this->params['project'])){
App::import('Model', 'Project');
$projectNames = new Project;
$projectNames->contain();
$projectInfo = $projectNames->find('first', array('conditions' => array('Project.slug' => $this->params['project'])));
$project_id = $projectInfo['Project']['id'];
$this->set('project_name_for_layout', $projectInfo['Project']['name']);
return $project_id;
}
}
And I utilize it in my other controllers:
function overview(){
$this->layout = 'project';
// Getting currentProject id from App Controller
$project_id = parent::__currentProject();
// Finding out what time it is and performing queries based on time.
$nowStamp = time();
$nowDate = date('Y-m-d H:i:s' , $nowStamp);
$twoWeeksFromNow = $nowDate + 1209600;
$lateMilestones = $this->Project->Milestone->find('all', array('conditions'=>array('Milestone.project_id' => $project_id, 'Milestone.complete'=> 0, 'Milestone.duedate <'=> $nowDate)));
$this->set(compact('lateMilestones'));
$currentProject = $this->Project->find('all', array('conditions'=>array('Project.slug' => $this->params['project'])));
$this->set(compact('currentProject'));
}
For your project you can try using a route like this at the end of your routes.php file:
Router::connect('/:groupname/:controller/:action/*', array(), array('groupname' => '[a-zA-Z0-9\-]+'));
// Notice I removed "/project" from the beginning. If you put the :groupname first, as I've done in the last example, then you only have one option for these custom url routes.
Then modify the other code to your needs.
If this is a public site, you may want to consider using named variables. This will allow you to define the group on the URL still, but without additional functionality requirements.
http://example.com/team/group:hr
http://example.com/team/action/group:hr/other:var
It may require custom routes too... but it should do the job.
http://book.cakephp.org/view/541/Named-parameters
http://book.cakephp.org/view/542/Defining-Routes
SESSIONS
Since web is stateless, you will need to use sessions (or cookies). The question you will need to ask yourself is how to reflect the selection (or not) of a specific department. It could be as simple as putting a drop down selection in the upper right that reflects ALL, HR, Sales, etc. When the drop down changes, it will set (or clear) the Group session variable.
As for the functionality in the controllers, you just check for the Session. If it is there, you limit the data by the select group. So you would use the same URLs, but the controller or model would manage how the data gets displayed.
// for all functionality use:
http://www.example.com/Team/action/id
http://www.example.com/Task/action/id
http://www.example.com/Equipment/action/id
You don't change the URL to accommodate for the functionality. That would be like using a different URL for every USER wanting to see their ADDRESS, PHONE NUMBER, or BILLING INFO. Where USER would be the group and ADDRESS, PHONE NUMBER< and BILLING INFO would be the item sets.
WITHOUT SESSIONS
The other option would be to put the Group filter on each page. So for example on Team/index view you would have a group drop down to filter the data. It would accomplish the same thing without having to set and clear session variables.
The conclusion is and the key thing to remember is that the functionality does not change nor does the URLs. The only thing that changes is that you will be working with filtered data sets.
Does that make sense?