I have a model DeferredHost, which also has an attribute ignore_flag. At the present, I'm just getting all of the deferred hosts in my controller:
#deferred_hosts = #company.deferred_hosts.last(5)
However, I'd like to make it subjective and only get the last 5 deferred hosts that have the ignore_flag = true.
How can I go about doing this? Should I use an if statement and loop through each deferred host, or is there a more 'Rails' way?
You can use where to make the query more specific:
#deferred_hosts = #company.deferred_hosts.where(ignore_flag: true).last(5)
Related
I'm not sure if this is just a lacking of the Rails language, or if I am searching all the wrong things here on Stack Overflow, but I cannot find out how to add an attribute to each record in an array.
Here is an example of what I'm trying to do:
#news_stories.each do |individual_news_story|
#user_for_record = User.where(:id => individual_news_story[:user_id]).pluck('name', 'profile_image_url');
individual_news_story.attributes(:author_name) = #user_for_record[0][0]
individual_news_story.attributes(:author_avatar) = #user_for_record[0][1]
end
Any ideas?
If the NewsStory model (or whatever its name is) has a belongs_to relationship to User, then you don't have to do any of this. You can access the attributes of the associated User directly:
#news_stories.each do |news_story|
news_story.user.name # gives you the name of the associated user
news_story.user.profile_image_url # same for the avatar
end
To avoid an N+1 query, you can preload the associated user record for every news story at once by using includes in the NewsStory query:
NewsStory.includes(:user)... # rest of the query
If you do this, you won't need the #user_for_record query — Rails will do the heavy lifting for you, and you could even see a performance improvement, thanks to not issuing a separate pluck query for every single news story in the collection.
If you need to have those extra attributes there regardless:
You can select them as extra attributes in your NewsStory query:
NewsStory.
includes(:user).
joins(:user).
select([
NewsStory.arel_table[Arel.star],
User.arel_table[:name].as("author_name"),
User.arel_table[:profile_image_url].as("author_avatar"),
]).
where(...) # rest of the query
It looks like you're trying to cache the name and avatar of the user on the NewsStory model, in which case, what you want is this:
#news_stories.each do |individual_news_story|
user_for_record = User.find(individual_news_story.user_id)
individual_news_story.author_name = user_for_record.name
individual_news_story.author_avatar = user_for_record.profile_image_url
end
A couple of notes.
I've used find instead of where. find returns a single record identified by it's primary key (id); where returns an array of records. There are definitely more efficient ways to do this -- eager-loading, for one -- but since you're just starting out, I think it's more important to learn the basics before you dig into the advanced stuff to make things more performant.
I've gotten rid of the pluck call, because here again, you're just learning and pluck is a performance optimization useful when you're working with large amounts of data, and if that's what you're doing then activerecord has a batch api you should look into.
I've changed #user_for_record to user_for_record. The # denote instance variables in ruby. Instance variables are shared and accessible from any instance method in an instance of a class. In this case, all you need is a local variable.
Program.where(name: "xxyyzz123") will return a collection, even if there's just one record that matches which forces me to do ugly things like:
puts Program.where(name: "xxyyzz123").first.age
or
puts Program.where(name: "xxyyzz123")[0].age
When I know for sure only one record will match, is there a shorter way to grab a property from that one record?
ActiveRecord's dynamic attribute-based finders (find_by_x) allow you to select the first record that matches in your database. For example:
Program.find_by_name('xxyyzz123')
will return the first record with name = 'xxyyzz123'
Note that these finders are 'mildly deprecated' in Rails 4. Using
Program.find_by(name: 'xxyyzz123")
achieves the same thing and may make it easier when needing to update to the next version of Rails if they ever remove the former's functionality.
See ActiveRecord::Base in the API for more.
Yes, you will have to access that with Program.where(name: "xxyyzz123").first.age, however, in Rails 3, it is usually recommended to do that type of query with: Program.find_by_name('xxyyzz123').age.
Rails 4 deprecates the above syntax and recommends you to use the following syntax for that:
Program.find_by(name: 'xxyyzz123')
If you have multiple conditions, then simply : Program.find_by(name: 'xxyyzz123', lang: 'ruby')
Behind the scene, it does the same tomfoolery - where clause and returns first object.
Is it possible to query unsaved changes using Rail's ActiveRecord or another similar approach?
An example of a Ruby interactive session is below. What I'd like to see, is the fourth line show a result of '999' instead of '10'. I'm use to using .NET and Entity Framework where something similar to this was possible. Perhaps in Ruby there is a better or different way to do the same thing. I could obviously add up the sum in a loop, but I find the query syntax more elegant. Any help is appreciated.
i = Inventory.where(:product_id => 1)
i.sum(:available) => 10
i.first.available = 999
i.sum(:available) => 10
No, since sum() is actually translated to SQL and run on the db, you must save the record to the db in order for the query to return the result you want.
Alternatively, you can use the Enumerable#sum method in ActiveSupport, which takes a block, like so:
all = Inventory.where(:product_id => 1).to_a
all.first.available = 999
all.sum(&:available)
Seems like it should be able to look at a simple tutorial or find an aswer with a quick google, but I can't...
codes = PartnerCode.find_by_sql "SELECT * from partner_codes where product = 'SPANMEX' and isused = 'false' limit 1"
I want the column named code, I want just the value. Tried everything what that seems logical. Driving me nuts because everything I find shows an example without referencing the actual values returned
So what is the object returned? Array, hash, ActiveRecord? Thanks in advance.
For Rails 4+ (and a bit earlier I think), use pluck:
Partner.where(conditions).pluck :code
> ["code1", "code2", "code3"]
map is inefficient as it will select all columns first and also won't be able to optimise the query.
You need this one
Partner.where( conditions ).map(&:code)
is shorthand for
Partner.where( conditions ).map{|p| p.code}
PS
if you are often run into such case you will like this gem valium by ernie
it gives you pretty way to get values without instantiating activerecord object like
Partner.where( conditions ).value_of :code
UPDATED:
if you need access some attribute and after that update record
save instance first in some variable:
instance=Partner.where( conditions ).first
then you may access attributes like instance.code and update some attribute
instance.update_attribute || instance.update_attributes
check documentation at api.rubyonrails.org for details
I'm trying to update one of my objects in my rails app and the changes just don't stick. There are no errors, and stepping through with the debugger just reveals that it thinks everything is updating.
Anyway, here is the code in question...
qm = QuestionMembership.find(:first, :conditions => ["question_id = ? AND form_id = ?", q_id, form_id])
qm.position = x
qm.save
For reference sake, QuestionMembership has question_id, form_id, and position fields. All are integers, and have no db constraints.
That is basically my join table between Forms and Questions.
Stepping through the code, qm gets a valid object, the position of the object does get changed to the value of x, and save returns 'true'.
However, after the method exits, the object in the db is unchanged.
What am I missing?
You may not be finding the object that you think you are. Some experimenting in irb might be enlightening.
Also, as a general rule when changing only one attribute, it's better to write
qm.update_attribute(:position, x)
instead of setting and saving. Rails will then update only that column instead of the entire row. And you also get the benefit of the data being scrubbed.
Is there an after_save?
Is the correct SQL being emitted?
In development log, you can actually see the sql that is generated.
For something like this:
qm = QuestionMembership.find(:first, :conditions => ["question_id = ? AND form_id = ?", q_id, form_id])
qm.position = x
qm.save
You should see something to the effect of:
SELECT * FROM question_memberships WHERE question_id=2 AND form_id=6 LIMIT 1
UPDATE question_memberships SET position = x WHERE id = 5
Can you output what sql you are actually seeing so we can compare?
Either update the attribute or call:
qm.reload
after the qm.save
What is the result of qm.save? True or false? And what about qm.errors, does that provide anything that makes sense to you? And what does the development.log say?
I have run into this problem rather frequently. (I was about to say consistently, but I cannot, as that would imply that I would know when it was about to happen.)
While I have no solution to the underlying issue, I have found that it seems to happen to me only when I am trying to update mysql text fields. My workaround has been to set the field to do something like:
qm.position = ""
qm.save
qm.position = x
qm.save
And to answer everyone else... when I run qm.save! I get no errors. I have not tried qm.save?
When I run through my code in the rails console everything works perfectly as evidenced by re-finding the object using the same query brings the expected results.
I have the same issue when using qm.update_attribute(... as well
My workaround has gotten me limping this far, but hopefully someone on this thread will be able to help.
Try changing qm.save to qm.save! and see if you get an exception message.
Edit: What happens when you watch the log on the call to .save!? Does it generate the expected SQL?
Use ./script/console and run this script.. step by step..
see if the position field for the object is update or not when you run line 2
then hit qm.save or qm.save!... to test
see what happens. Also as mentioned by Tim .. check the logs
Check your QuestionMembership class and verify that position does not have something like
attr_readonly :position
Best way to debug this is to do
tail -f log/development.log
And then open another console and do the code executing the save statement. Verify that the actual SQL Update statement is executed.
Check to make sure your database settings are correct. If you're working with multiple databases (or haven't changed the default sqlite3 database to MySQL) you may be working with the wrong database.
Run the commands in ./script/console to see if you see the same behavior.
Verify that a similar object (say a Form or Question) saves.
If the Form or Question saves, find the difference between the QuestionMembership and Form or Question object.
Turns out that it was emitting the wrong SQL. Basically it was looking for the QuestionMembeship object by the id column which doesn't exist.
I was under the impression that that column was unnecessary with has_many_through relationships, although it seems I was misguided.
To fix, I simply added the id column to the table as a primary key. Thanks for all the pointers.