I'm using Rails to search through a SQLite table (for other reasons I can't use the standard database-model system) using a SELECT query like so:
info = ActiveRecord::Base.connection.execute("SELECT * FROM #{form_name} WHERE EmailAddress = \"#{user_em}\";")
This returns the correct values, but for some reason the output is in duplicate, the difference being the 2nd set doesn't have column titles in the hash, instead going from 0-[num columns]. For example:
{"id"=>1, "Timestamp"=>"2/27/2017 14:26:03", "EmailAddress"=>"-snip-", 0=>1, 1=>"2/27/2017 14:26:03", 2=>"-snip-"}
(I'll note the obvious- there's only one row in the table with that information in it)
While it's not exactly a fatal problem, I'm interested as to why it's doing so and if it's possible to prevent it. Thanks!
This allows you to read the values both by column index or column name:
id = row[0]
timestamp = row["Timestamp"]
Related
I need to find a way to display all Vacancies from my Vacancy model except the ones that a user already applied for.
I keep the IDs of the vacancies a certain user applied for in a seperate model AppliedVacancies.
I was thinking something line the lines of:
#applied = AppliedVacancies.where(employee_id: current_employee)
#appliedvacancies_id = []
#applied.each do |appliedvacancy|
#appliedvacancies_id << appliedvacancy.id
end
#notyetappliedvacancies = Vacancy.where("id != ?", #appliedvacancy_id)
But it does not seem to like getting an array of IDs. How would I go about fixing this?
I get following error:
PG::DatatypeMismatch: ERROR: argument of WHERE must be type boolean, not type record
LINE 1: SELECT "vacancies".* FROM "vacancies" WHERE (id != 13,14)
^
: SELECT "vacancies".* FROM "vacancies" WHERE (id != 13,14)
This is purely an SQL problem.
You cannot use != to compare a value to a set of values. You need to use the IN operator.
#notyetappliedvacancies = Vacancy.where("id NOT IN (?)", #appliedvacancy_id)
As an aside, you can drastically improve the code you've written so far. You are needlessly instantiating complete ActiveRecord models for every record found in your applied_vacancies table, when all you need are the IDs.
A first pass at improvement would be to use pluck to skip the entire process and go straight to the list of IDs:
ids = AppliedVacancies.where(employee_id: current_employee).pluck(:id)
#notyetappliedvacancies = Vacancy.where("id NOT IN (?)", ids)
Next, you can go a step further and eliminate the first query all together (or rather, combine it with the last query as a sub-query) by leaving it as an AREL projection which can be subbed into the second query directly:
ids = AppliedVacancies.select(:id).where(employee_id: current_employee)
#notyetappliedvacancies = Vacancy.where("id NOT IN (?)",App)
This will generate a single query:
select * from vacancies where id not in (select id from applied_vacancies where employee_id = <value>)
Answer like #meagar, but Rails 4 way:
#notyetappliedvacancies = Vacancy.where.not(id: #appliedvacancy_id)
I would like to understand why in Rails 4 (4.2.0) I see the following behaviour when manipulating data in a join table:
student.student_courses
returns all associated records of courses for a given user;
but the following will save changes
student.student_courses[0].status = "attending"
student.student_courses[0].save
while this will not
student.student_courses.find(1).status = "attending"
student.student_courses.find(1).save
Why is that, why are those two working differently, is the first one the correct way to do it ?
student.student_courses[0] and student.student_courses.find(1) are subtly different things.
When you say student.student_courses, you're just building a query in an ActiveRecord::Relation. Once you do something to that query that requires a trip to the database, the data is retrieved. In your case, that something is calling [] or find. When you call []:
student.student_courses[0]
your student will execute the underlying query and stash all the student_courses somewhere. You can see this by looking at:
> student.student_courses[0].object_id
# and again...
> student.student_courses[0].object_id
# same number is printed twice
But if you call find, only one object is retrieved and a new one is retrieved each time:
> student.student_courses.find(1).object_id
# and again...
> student.student_courses.find(1).object_id
# two different numbers are seen
That means that this:
student.student_courses[0].status = "attending"
student.student_courses[0].save
is the same as saying:
c = student.student_courses[0]
c.status = "attending"
c.save
whereas this:
student.student_courses.find(1).status = "attending"
student.student_courses.find(1).save
is like this:
c1 = student.student_courses.find(1)
c1.status = "attending"
c2 = student.student_courses.find(1)
c2.save
When you use the find version, you're calling status= and save on entirely different objects and since nothing was actually changed in the one that you save, the save doesn't do anything useful.
student_courses is an ActiveRecord::Relation, basically a key => value store. The find method would only work on a model
Hopefully this is a little clearer. I'm sorry but I'm very new to coding in general. I have multiple tables that I have to query in succession in order to get to the correct array that I need. The following logic for the query is as follows:
this gives me an array based upon the store :id
store = Stores.find(params[:id])
this gives me another array based upon the param .location found in the table store where that value equals the row ID in the table Departments
department = Departments.find(store.location)
I need to preform one last query but in order to do so I need to figure out which day of the meeting is needed. In order to do this I have to create the parameter day_of_meeting found in the table Stores. I try to call it from the array above and create a new variable. In the Table Departments, I there are params such as day_1, day_2 and so on. I need to be able to call something like department.day_1 or department.day_2. Thus, I'm trying to actually create the variable by join the words "department.day_" to the variable store.day_of_meeting which would equal some integer, creating department.day_1...
which_day = ["department.day_", store.day_of_meeting].join("")
This query finds uses the value found from the variable department.day_1 to query table Meeting to find the values in the corresponding row.
meeting = Meeting.find(which_day)
Does this make my problem any clearer to understand?
findmethod can only accept parameters like Meeting.find(1) or Meeting.find("1-xx").
so, what you need is Meeting.find(department.send("day_" + store.day_of_meeting.to_s))
Hope to help!
So I am pulling my hair over this issue / gotcha. Basically I used find_by_sql to fetch data from my database. I did this because the query has lots of columns and table joins and I think using ActiveRecord and associations will slow it down.
I managed to pull the data and now I wanted to modify returned values. I did this by looping through the result ,for example.
a = Project.find_by_sql("SELECT mycolumn, mycolumn2 FROM my_table").each do |project|
project['mycolumn'] = project['mycolumn'].split('_').first
end
What I found out is that project['mycolumn'] was not changed at all.
So my question:
Does find_by_sql return an array Hashes?
Is it possible to modify the value of one of the attributes of hash as stated above?
Here is the code : http://pastie.org/4213454 . If you can have a look at summarize_roles2() that's where the action is taking place.
Thank you. Im using Rails 2.1.1 and Ruby 1.8. I can't really upgrade because of legacy codes.
Just change the method above to access the values, print value of project and you can clearly check the object property.
The results will be returned as an array with columns requested encapsulated as attributes of the model you call this method from.If you call Product.find_by_sql then the results will be returned in a Product object with the attributes you specified in the SQL query.
If you call a complicated SQL query which spans multiple tables the columns specified by the SELECT will be attributes of the model, whether or not they are columns of the corresponding table.
Post.find_by_sql "SELECT p.title, c.author FROM posts p, comments c WHERE p.id = c.post_id"
> [#<Post:0x36bff9c #attributes={"title"=>"Ruby Meetup", "first_name"=>"Quentin"}>, ...]
Source: http://api.rubyonrails.org/v2.3.8/
Have you tried
a = Project.find_by_sql("SELECT mycolumn, mycolumn2 FROM my_table").each do |project|
project['mycolumn'] = project['mycolumn'].split('_').first
project.save
end
Ruby 1.9.2 / rails 3.1 / deploy onto heroku --> posgresql
Hi, Once a number of rows relating to an object goes over a certain amount, I wish to pull back every nth row instead. It's simply because the rows are used (in part) to display data for graphing, so once the number of rows returned goes above say 20, it's good to return every second one, and so forth.
This question seemed to point in the right direction:
ActiveRecord Find - Skipping Records or Getting Every Nth Record
Doing a mod on row number makes sense, but using basically:
#widgetstats = self.widgetstats.find(:all,:conditions => 'MOD(ROW_NUMBER(),3) = 0 ')
doesn't work, it returns an error:
PGError: ERROR: window function call requires an OVER clause
And any attempt to solve that with e.g. basing my OVER clause syntax on things I see in the answer on this question:
Row numbering in PostgreSQL
ends in syntax errors and I can't get a result.
Am I missing a more obvious way of efficiently returning every nth task or if I'm on the right track any pointers on the way to go? Obviously returning all the data and fixing it in rails afterwards is possible, but terribly inefficient.
Thank you!
I think you are looking for a query like this one:
SELECT * FROM (SELECT widgetstats.*, row_number() OVER () AS rownum FROM widgetstats ORDER BY id) stats WHERE mod(rownum,3) = 0
This is difficult to build using ActiveRecord, so you might be forced to do something like:
#widgetstats = self.widgetstats.find_by_sql(
%{
SELECT * FROM
(
SELECT widgetstats.*, row_number() OVER () AS rownum FROM widgetstats ORDER BY id
) AS stats
WHERE mod(rownum,3) = 0
}
)
You'll obviously want to change the ordering used and add any WHERE clauses or other modifications to suit your needs.
Were I to solve this, I would either just write the SQL myself, like the SQL that you linked to. You can do this with
my_model.connection.execute('...')
or just get the id numbers and find by id
ids = (1..30).step(2)
my_model.where(id => ids)