I have code to run sql query in ruby as follows
sql =
ActiveRecord::Base.connection()
sql.begin_db_transaction
report = sql.execute("select * from users;")
sql.commit_db_transaction
So after this report is an Mysql::object. Now I want to extract all fields and its corresponding data to array or hash.
thanks,
execute method should produce a result which gives you a method called all_hashes - it will return an array of hashes corresponding to the rows of query's results, which seems to be what you need. So, call
report.all_hashes
Related
I am hardly trying to find one comparison of result.blank? and result[0] so finally today when i was checking one query with these two methods.
Here the code, result variable is #categories, which is an ActiveRecord result
This blank check calling one extra db call like SELECT COUNT(*) AS count_all
if #categories.blank?
end
But here that extra query is not showing there.
if #categories[0]
end
Is there any logic behind that? I couldn't find that
It is important to note that assigning a ActiveRecord query to a variable does not return the result of the query. Something like this:
#categories = Category.where(public: true)
Does not return an array with all categories that are public. Instead it returns an Relation which defines an query. The query to the database is execute once you call a method in the relation that needs to return the actual record, for example each, load, count.
That said: When you call blank? on a relation Rails needs to know it the relation will not return an empty array. Therefore Rails executes an query like:
SELECT COUNT(*) FROM categories WHERE public = 1
Because that queries is much faster that fetching all records when the only thing you need to know if there are any matching records.
Whereas #categories[0] works differently. Here it need to load all records to have an array holding all macthing categories and than return the first record in that array.
At this point both version ran only on query to the database. But I guess your next step would be to iterate over the records if there were any. If you used the first version (blank?) then the objects were not loaded, they were only counted. Therefore Rails would need to query for the actual records, what would result in a second query. The second exmaple ([0]) has the records already loaded, therefore not seconds query in needed.
I’m using Rails 4.2.7. I have an array of my model objects and currently I’m iterating through that array to find matching entries in the database based on a field my each object …
my_object_times.each_with_index do |my_object_time, index|
found_my_object_time = MyObjectTime.find_by_my_object_id_and_overall_rank(my_object_id, my_object_time.overall_rank)
My question is, how can I rewrite the above to run one query instead of N queries, if N is the size of the array. What I wanted was to force my underlying database (PostGres 9.5) to do a “IF VALUE IN (…)” type of query but I’m not sure how to extract all the attributes from my array and then pass them in appropriately to a query.
I would do something like this:
found_my_object_times = MyObjectTime.where(
object_id: my_object_id,
overall_rank: my_object_times.map(&:overall_rank)
)
I have a model called Record and belongs Product model,
the price column type is hexadecimal. Rails already convert it to string in view. But I wanna get them in my console queries.
Example code for pluck:
Product.first.records.pluck(:price)
This query displays the values in array as hexadecimal. There is a method called to_sentences for pluck values but its not enough for my case.
The problem is same in collect method:
Product.first.records.collect(&:price)
What is the pluck query to display my hexadecimal data as array of strings like:
["45,46","75,42"]
Product.first.records.pluck(:price).map(&:to_s)
please try this:
Product.first.records.pluck(:price).join(',')
I am writing an app that needs to quickly process hundreds of thousands of rows of data, so I've looked into nesting raw SQL in my Ruby code using ActiveRecord::Base.connection.execute, which is working beautifully. However whenever I run it I get the following Object as a result:
#<PG::Result:0x007fe158ab18c8 status=PGRES_TUPLES_OK ntuples=0 nfields=1 cmd_tuples=0>
I've googled around and can't find a way to parse the PG Result into something actually useful. Is there any built-in PG way to do this, or a workaround, or anything really?
Here is the query I'm using:
SELECT row_to_json(row(company_name, ccn_short_title, title))
FROM contents
WHERE contents.company_name = '#{company_name}'
AND contents.title = '#{title}';
Actually PG::Result responds to many well-known methods from Enumerable module. You can output them all to watch for the desired ones:
query = "SELECT row_to_json(row) from (select * from users) row"
result = ActiveRecord::Base.connection.execute(query)
result.methods - Object.methods
# => returns an array of methods which can be used
For example, you could iterate the results and map them to something more suitable...
result.map do |row|
JSON.parse(row["row_to_json"])
end
# => returns familiar hashes
Get a desired result hash by its index...
result[0]
And much more.
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