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.
Related
I'm having trouble with a little Ruby on Rails I'm building and need some help.
I have a Table with 20+ Columns and a corresponding XML File which can be parsed as some sort of hash with a gem. Every key would be mapped to a column and every value would be a data record in said column.
The way I access a specific value in the already parsed XML file is:
filename["crs","inputkeyhere"]
which returns the value, for example "52" or whatever.
What I am trying to do is upload the file, parse it with the gem and give each column the corresponding value.
My table (or model) is called "Attributeset" and I already know how I can access every column:
#attributeset = Attributeset.new
#attributeset.attributes.keys
So my thought process was:
Iterate over all the keys
Pass every key into a block called |a|
Use the rails possibilty to set attributes by calling the corresponding #attributeset.
Set colum attribute to the corresponding xml key
So my code would go something like this:
#attributeset.attributes.keys.each do |a|
#attributeset.a=filename["crs",a]
end
But my problem is, that ruby thinks ".a" is a method and apparently does not evaluate "a" to the block parameter.
I've read through lambdas and procs and whatnot but didn't really understand how they could work for my specific situation.
Coming from bash scripting maybe my thinking might be wrong but I thought that the .a might get evaluated.
I know I can run the block with yield, but this only works in methods as far as I know..
Any help is appreciated.
Thanks and stay healthy,
Alex
Thanks for the input!
I wanted to make it as clean as possible, and not using any temporary hashes to pass arguments.
I've found the method
write_attribute
which can be used like this:
#attributeset.write_attribute(a, xmp["crs",a])
worked perfectly for me.
You can use []= method to set values dynamically:
#attributeset.attribute_names.each do |attribute|
#attributeset[attribute] = filename["crs", attribute]
end
I want to query some data from table based on user for submission.
Its working fine but if I post nothing in the the fields and post my form, it returns me nil exception.
Is there a way we can deal with nil exception, or do I need to change query?
question_options = question.question_options.where(id: self.option_id).first
The simplest solution is to use try. For example:
question_options = question.question_options.where(id: self.option_id).try(:first)
The documentation for try is here
For your issue multiple solutions exists. Your query returns nil and thats ok because nothing was found. The simplest solution is an if statement. if question_options.nil? do some thing else. Or you can use an unitialized object (or a NullObject) do work with it question_option = question.question_options.where(id: self.option_id).first || QuestionOption.new
The are other possibilites too. It depends on your requirement what way you choose.
I have the following code in a rails model:
foo = Food.find(...)
foo.with_lock do
if bar = foo.bars.find_by_stuff(stuff)
# do something with bar
else
bar = foo.bars.create!
# do something with bar
end
end
The goal is to make sure that a Bar of the type being created is not being created twice.
Testing with_lock works at the console confirms my expectations. However, in production, it seems that in either some or all cases the lock is not working as expected, and the redundant Bar is being attempted -- so, the with_lock doesn't (always?) result in the code waiting for its turn.
What could be happening here?
update
so sorry to everyone who was saying "locking foo won't help you"!! my example initially didin't have the bar lookup. this is fixed now.
You're confused about what with_lock does. From the fine manual:
with_lock(lock = true)
Wraps the passed block in a transaction, locking the object before yielding. You pass can the SQL locking clause as argument (see lock!).
If you check what with_lock does internally, you'll see that it is little more than a thin wrapper around lock!:
lock!(lock = true)
Obtain a row lock on this record. Reloads the record to obtain the requested lock.
So with_lock is simply doing a row lock and locking foo's row.
Don't bother with all this locking nonsense. The only sane way to handle this sort of situation is to use a unique constraint in the database, no one but the database can ensure uniqueness unless you want to do absurd things like locking whole tables; then just go ahead and blindly try your INSERT or UPDATE and trap and ignore the exception that will be raised when the unique constraint is violated.
The correct way to handle this situation is actually right in the Rails docs:
http://apidock.com/rails/v4.0.2/ActiveRecord/Relation/find_or_create_by
begin
CreditAccount.find_or_create_by(user_id: user.id)
rescue ActiveRecord::RecordNotUnique
retry
end
("find_or_create_by" is not atomic, its actually a find and then a create. So replace that with your find and then create. The docs on this page describe this case exactly.)
Why don't you use a unique constraint? It's made for uniqueness
A reason why a lock wouldn't be working in a Rails app in query cache.
If you try to obtain an exclusive lock on the same row multiple times in a single request, query cached kicks in so subsequent locking queries never reach the DB itself.
The issue has been reported on Github.
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
Hey everyone... I've been out of the game for awhile so you're going to have to excuse the fact that it's Rails2.3
Currently the app is running 2.3.3, I just updated it to 2.3.11
An object is edited, and saved using the .save command and the SQL generated in the logs is as follows:
UPDATE `calc_sheets` SET `is_us_connection` = 0, `holding_date_end` = '0001-02-11', `updated_on` = '2011-03-16 13:14:00', `extra_chars` = '' WHERE `id` = 657
however for some reason the created_on field is getting updated, and obviously shouldn't be. Is there some bug that I'm not aware of. I did some searching, looking and reading and nothing jumped out at me.
This is the only SQL call made during the action, so it's not as if something else is being updated or saved.
Any advice?
I realize this is out dated code, the app is fairly old, and the clients aren't ready to updated it... this "bug" however is causing all kinds of havoc.
Thanks in advance for any advice.
My guess is that the created_on table column is set to on "on update CURRENT_TIMESTAMP" (assuming mySQL) or something equivalent.