I have a column name in database which holds strings like CVM™ what I want to do is to split it so everything after ampersand goes into a different column and everything before the string stays where it was. The final result should put ™ into a column called abbr and save CVM into name column.
Create a rake task file
lib/tasks/split_name.rake
Then paste in the following, and change "TableName" to your actual table name.
task :split_name => :environment do
TableName.all.each do |r|
a = r.name.split("&") #assuming exact same string format, and not null
r.update_attribute(:name, a[0])
r.update_attribute(:abbr, '&' + a[1])
end
end
Then run it as such
rake split_name
Must this be done Rails level? You can also do this with just Postgres with split_part function. I assume you're working with users table:
ALTER TABLE users ADD COLUMN abbr VARCHAR;
UPDATE users
SET name = SPLIT_PART(name, '™', 1),
abbr = '™' || SPLIT_PART(name, '™', 2);
You can also bake these queries into a Rake task if needed.
Update: Opps I assumed you were using Postgres. But other languages should have similar method that you can use.
Related
I have a table(Users). In one of its columns(configs) i added a default value ("A"=>0) through a migration. Now all the new users i create have default value of A but the old users don't. I want to backfill the default value of A for the old users using migration. How do I do that?
given:
t.jsonb "configs", default: {"B"=>7, "C"=>10, "D"=>10}
This is my existing column. Here B, C and D have different values for different Users. I want to make it into
t.jsonb "configs", default: {"B"=>7, "C"=>10, "D"=>10, "A"=>0}
where the values of B, C and D stays the same for all Users but just the default value of "A" gets added to the existing json in the column.
rails - 4.2.11
db - postgres
I have gone through some documentations but couldn't find a comprehensive answer. Any help is appreciated.
From your comments is sounds like you want to update a JSONB column to have a new set of defaults, and any existing json hashes get the new key/value pair of "A": 0 added to the current value. A migration can change the DB but you will need to do it programmatically to update the rows that have values already, especially because their values are not all the same. With that said it could be something like:
User.all.each do |u|
u.configs["A"] = 0
u.save
end
This will iterate through all of the users and set the value of "a" to zero. If no "a" exists in the hash it will add it with the value of zero without touching anything else in the JSON. If "a" already exists for a user it will be set to zero. So if you have users whose value for "a" has already changed from the default of zero you can avoid them with:
User.all.each do |u|
unless conifigs["A"] # if "A" already exists skip this
u.configs["A"] = 0
u.save
end
end
Please read https://nandovieira.com/using-postgresql-and-jsonb-with-ruby-on-rails for information on how to leverage JSONB in Rails. It is a very powerful tool if you put in the code to really get the most use out of it. Be sure and read the part about store_accessor, it would help you to do a lot more with that JSONB column.
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"]
I have an API that has a database with UPC-12 values in it. Sometimes API calls will come in with UPC-10 codes. My db upc column is bigint, so it removes the leading 0 on a UPC-12 value. That leaves the last digit as a wildcard when comparing to UPC-10.
I'd like to be able to check a UPC-10 value against records in the db to see if there's a match. Since I can't use LIKE, how do I do that?
The goal is to do something like:
def self.pull_product(upc)
upc_string = upc.to_s
if upc_string.length == 10
# product = Product.where... use a wildcard to try and match to existing record
else
product = Product.find_by_upc(upc)
end
end
This Rails 4 and Postgresql.
Just to clarify:
I might have a UPC-10 api call with a upc param like: 7618600002. My database has the UPC-12 equivalent: 76186000023. So if I just query for the param in the api call, I'll get nil.
I need a way to match the the UPC-10 param against my UPC-12 value in the database.
You need to use SQL like this:
upc between upc_string::int*10 and upc_string::int*10+9
I have no idea how to code it in Rails though.
I have a typical set of models with a parent/child/grandchild/ggrand hierarchy. I create the relation with:
#summary = Function.joins(:benchmrks=>{:indicators=>:results})
.select("functions.id , benchmrks.id , indicators.id , avg(results.score) ")
.group("results.indicator_id")
I had trouble accessing columns in my result set so I did this:
#summary.each do |s|
s.attributes
end
and I see two columns defined and they are both accessible:
{"id"=>1, "avg(results.score)"=>3.0}
if I change my .select() and manually rename the columns to:
.select("functions.id as f_id, benchmrks.id as b_id, indicators.id as i_id , avg(results.score) as avg")
I see 4 columns and they are all accessible:
{"f_id"=>1, "b_id"=>1, "i_id"=>1, "avg"=>3.0}
so the dot SQL syntax of column names (functions.id, benchmrks.id, and indicators_id) seem to get collapsed into a single id by rails. This was unexpected behavior to me.
Should I have done this a different way?
Say I have a model called Transaction which has a :transaction_code attribute.
I want that attribute to be automatically filled with a sequence number which may differ from id (e.g. Transaction with id=1 could have transaction_code=1000).
I have tried to create a sequence on postgres and then making the default value for the transaction_code column the nextval of that sequence.
The thing is, if I do not assign any value to #transaction.transaction_code on RoR, when I issue a #transaction.save on RoR, it tries to do the following SQL:
INSERT INTO transactions (transaction_code) VALUES (NULL);
What this does is create a new row on the Transactions table, with transaction_code as NULL, instead of calculating the nextval of the sequence and inserting it on the corresponding column. Thus, as I found out, if you specify NULL to postgres, it assumes you really want to insert NULL into that column, regardless of it having a default value (I'm coming from ORACLE which has a different behavior).
I'm open to any solution on this, either if it is done on the database or on RoR:
either there is a way to exclude attributes from ActiveRecord's
save
or there is a way to change a column's value before insert with a trigger
or there is a way to generate these sequence numbers within RoR
or any other way, as long as it works :-)
Thanks in advance.
For the moment, you might be stuck fetching and assigning the sequence in your ROR model like this:
before_create :set_transaction_code_sequence
def set_transaction_code_sequence
self.transaction_code = self.class.connection.select_value("SELECT nextval('transaction_code_seq')")
end
I'm not particularily fond of this solution, since I'd like to see this corrected in AR directly... but it does do the trick.
If you want to insert the default value in to a column in an INSERT statement, you can use the keyword DEFAULT - no quotes:
INSERT INTO mytable (col1, col2) VALUES (105, DEFAULT);
Or you could spell out the default, nextval(...) in your case. See the manual here.
A trigger for that case is simple. That's actually what I would recommend if you want to make sure that only numbers from your sequence are entered, no matter what.
CREATE OR REPLACE FUNCTION trg_myseq()
RETURNS trigger AS
$BODY$
BEGIN
NEW.mycol := nextval('my_seq');
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
CREATE TRIGGER myseq
BEFORE INSERT
ON mytable
FOR EACH ROW
EXECUTE PROCEDURE trg_myseq();
On a side note:
If you want to assign your own (non-sequential) numbers as 'sequence', I have written a solution for that in an answer a couple of days ago:
How to specify list of values for a postgresql sequence
I was still experiencing this issue with Rails7 - I could see that Rails was generating a NULL in the insert, but changing the column from integer to bigint solved it. - Rails then does not supply a value for my sequenced column and the DEFAULT nextval('number_seq') is used.