#user_post = Post.find(:all,:conditions => ["content LIKE ?", "%#{params[:query]}%"])
This particular statement returning nil even though there exists a record in the database. Where could be the problem?
Please help me out.
Have you verified that the parameters are being passed in correctly? When a query isn't returning expected results it is almost always because the query you think you are executing isn't really the query that you are executing. Take a look at your log files to verify the that the query is correct.
have you tried running resulting query in mysql console? if you do have result then keep debugging, error is somewhere between controller action and rendered view. maybe you're loading result in before_filter which is not executed for your action?
Related
I am trying to implement this solution in rails, using the collection aggregate method, to clone an entire collection within the same database.
In mongo shell, this works perfectly, and a cloned collection is created successfully:
db.source_collection.aggregate([ { $match: {} }, { $out: "target_collection" } ])
The rails-mongoid alternate, according to my research, should be this, which runs without errors:
SourceCollection.collection.aggregate({"$match" => {}, "$out" => "target_collection"})
#<Mongo::Collection::View::Aggregation:0x000000055bced0 #view=#<Mongo::Collection::View:0x44951600 namespace='DB_dev.source_collection' #filter={} #options={}>, #pipeline={"$match"=>{}, "$out"=>"target_collection"}, #options={}>
I also tried with an array
SourceCollection.collection.aggregate([{"$match" => {}}, {"$out" => "target_collection"}])
#<Mongo::Collection::View::Aggregation:0x000000054936d0 #view=#<Mongo::Collection::View:0x44342320 namespace='DB_dev.source_collection' #filter={} #options={}>, #pipeline=[{"$match"=>{}}, {"$out"=>"target_collection"}], #options={}>
UPDATE
This simplest syntax also works in Mongo console:
db.source_collection.aggregate( { $out: "target_collection" } )
But the respective syntax does not seem to work in Ruby:
SourceCollection.collection.aggregate({"$out" => "target_collection"})
Unfortunately, although there are no errors, the collection is not created.
Any clues as to the way I can make this happen?
Mongo gem version 2.5.3
Update2
Apparently $out is not considered in the pipeline, thus rendering the aggregation invalid.
This can be fixed with code... I am looking for a module/class/method override, as contacting mongodb issue tracking system for a change request might not be as quick..
UPDATE - FINAL
This issue has been solved, by help of Thomas R. Koll (thank you).
I add an update to post the response I got from the ticketing service of MongoDB, which pretty much describes Thomas's solution.
The reason you're not seeing the results without count is that the
aggregate method returns a lazy cursor; that is, the query does not
execute until the return value of aggregate is iterated over.
Calling count is one way to do this. This is the same behavior
you'll see if you call find or if you call aggregate without
specifying $out; the difference is that $out has an side-effect
beyond just returning the results, so it's more obvious when exactly
it occurs.
Found the solution, and I have to explain a few thigs:
This returns a Mongo::Collection::View::Aggregation object, it won't send a query to the database
User.collection.aggregate({"$out": "target_collection"})
Only when you call a method like count or to_a on the aggregation object it will be sent to the server, but if you pass a hash you'll get an error, so the pipeline has to be an array of hashes to work
User.collection.aggregate([{"$out": "target_collection"}]).count
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.
So I have an ActiveRecord query in a controller:
t="example_name"
i = Item.where(:name => t)
This doesn't cause an error, but it doesn't seem to be returning the right thing. In the rails console, it returns a normal Item and I can access all the attributes, but looking at some print statements I put in, I can see that
i.class = Item::ActiveRecord_Relation
Whereas when I make the call as
i = Item.find(4)
for debugging purposes,
i.class = Item
I can't figure out why this is happening, especially since the where() query works in the rails console
Anytime you use a #where query in Rails, it returns as an ActiveRecord::Relation. This is beneficial to you, because Rails is avoiding the performance overhead and just saying, "I found these results according to the query you gave me."
Here's a link to the Rails docs.
I want to run a raw SQL query as following:
ActiveRecord::Base.connection.execute(some_query);
Can I capture any errors that happen while executing the query? If yes, how?
Does execute returns anything? It doesn't say in the documentation.
Cheers
You can rescue errors as normal. For example:
begin
ActiveRecord::Base.connection.execute(some_query)
rescue
# do stuff with exception
end
Have a look at the MySql (for example) adapter's code to see what's going on.
In this case, execute returns a MySql::Result object.
execute method is typically implemented by respective database adapters and returns Result object from respective database libraries. So, if you are using Mysql the return value will be of type Mysql::Result.
Typically, if there is an error, the method will simply raise an exception which can be rescued.
I think I found the answer. Execute statement returns the error that it receives from the database and that can be captured in a variable and displayed.
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.