Using raw sql queries in Rails 3 application? - sql

Question

I am working on migrating a legacy database into my Rails application (3.2.3). The original database comes with quite a few long sql queries for reports. For now, what I would like to do it use the sql queries in the Rails application and then one by one (when time allows) swap the sql queries to 'proper' Rails queries.
I have a clinical model and the controller has the following code:
#clinical_income_by_year = Clinical.find_all_by_sql(SELECT date_format(c.transactiondate,'%Y') as Year,
date_format(c.transactiondate,'%b') as Month,
sum(c.LineBalance) as "Income"
FROM clinical c
WHERE c.Payments = 0 AND c.LineBalance <> 0
AND c.analysiscode <> 213
GROUP BY c.MonthYear;)
However, when I run that code I get a few errors to do with the formatting.
Started GET "/clinicals" for 127.0.0.1 at 2012-04-29 18:00:45 +0100
SyntaxError (/Users/dannymcclelland/Projects/premvet/app/controllers/clinicals_controller.rb:6: syntax error, unexpected tIDENTIFIER, expecting ')'
...rmat(c.transactiondate,'%Y') as Year,
... ^
/Users/dannymcclelland/Projects/premvet/app/controllers/clinicals_controller.rb:7: syntax error, unexpected tIDENTIFIER, expecting keyword_end
...rmat(c.transactiondate,'%b') as Month,
... ^
/Users/dannymcclelland/Projects/premvet/app/controllers/clinicals_controller.rb:8: syntax error, unexpected tIDENTIFIER, expecting keyword_end
... sum(c.LineBalance) as "Income"
... ^
/Users/dannymcclelland/Projects/premvet/app/controllers/clinicals_controller.rb:10: syntax error, unexpected tCONSTANT, expecting keyword_end
... WHERE c.Payments = 0 AND c.LineBalance <> 0
... ^
/Users/dannymcclelland/Projects/premvet/app/controllers/clinicals_controller.rb:10: syntax error, unexpected '>'
...yments = 0 AND c.LineBalance <> 0
... ^
/Users/dannymcclelland/Projects/premvet/app/controllers/clinicals_controller.rb:11: syntax error, unexpected '>'
... AND c.analysiscode <> 213
... ^
Is there something I should be doing to the sql query before importing it into the controller? Although it's possible there is something wrong with the query (It was written quite some time ago), it does work as expected when run directly within the database. It returns an array like this:
----------------------------------------------
| Year | Month | Income |
----------------------------------------------
----------------------------------------------
| 2012 | January | 20,000 |
| 2012 | February | 20,000 |
| 2012 | March | 20,000 |
| 2012 | April | 20,000 |
----------------------------------------------
etc..
Any help, advice or general pointers would be appreciated!
I'm reading through http://guides.rubyonrails.org/active_record_querying.html trying to convert the sql query to a correct Rails query.
So far I have matched the second to last line:
AND c.analysiscode <> 213
with
#clinical_income_by_year = Clinical.where("AnalysisCode != 213")
baby steps!
UPDATE
I've got the filtering sorted now, thanks to the Rails guide site but I'm stuck on the grouping and sum part of the sql query. I have the following so far:
#clinical_income_by_year = Clinical.where("AnalysisCode != 213 AND Payments != 0 AND LineBalance != 0").page(params[:page]).per_page(15)
I'm struggling to build in the following two lines of the sql query:
sum(c.LineBalance) as "Income"
and
GROUP BY c.MonthYear;)
My view code looks like this:
<% #clinical_income_by_year.each do |clinical| %>
<tr>
<td><%= clinical.TransactionDate.strftime("%Y") %></td>
<td><%= clinical.TransactionDate.strftime("%B") %></td>
<td><%= Clinical.sum(:LineBalance) %></td>
</tr>
<% end %>
</table>
<%= will_paginate #clinical_income_by_year %>

Answer 1

The Ruby parser doesn't understand SQL, you need to use a string:
#clinical_income_by_year = Clinical.find_by_sql(%q{ ... })
I'd recommend using %q or %Q (if you need interpolation) for this so that you don't have to worry about embedded quotes so much. You should also move that into a class method in the model to keep your controllers from worrying about things that aren't their business, this will also give you easy access to connection.quote and friends so that you can properly use string interpolation:
find_by_sql(%Q{
select ...
from ...
where x = #{connection.quote(some_string)}
})
Also, the semicolon in your SQL:
GROUP BY c.MonthYear;})
isn't necessary. Some databases will let it through but you should get rid of it anyway.
Depending on your database, the identifiers (table names, column names, ...) should be case insensitive (unless some hateful person quoted them when they were created) so you might be able to use lower case column names to make things fit into Rails better.
Also note that some databases won't like that GROUP BY as you have columns in your SELECT that aren't aggregated or grouped so there is ambiguity about which c.transactiondate to use for each group.
A more "Railsy" version of your query would look something like this:
#c = Clinical.select(%q{date_format(transactiondate, '%Y') as year, date_format(transactiondate, '%b') as month, sum(LineBalance) as income})
.where(:payments => 0)
.where('linebalance <> ?', 0)
.where('analysiscode <> ?', 213)
.group(:monthyear)
Then you could do things like this:
#c.each do |c|
puts c.year
puts c.month
puts c.income
end
to access the results. You could also simplify a little bit by pushing the date mangling into Ruby:
#c = Clinical.select(%q{c.transactiondate, sum(c.LineBalance) as income})
.where(:payments => 0)
.where('linebalance <> ?', 0)
.where('analysiscode <> ?', 213)
.group(:monthyear)
Then pull apart c.transactiondate in Ruby rather than calling c.year and c.month.