Active Record SQL View Support for SQL Server - Is this supp


#1

I’m just exploring ROR for the first time - so excuse me if that has
already been asked/answered. I’m intersted in developing a Web front
end to an existing SQL Server database - migrating this to MySql/
Postgres is NOT an option.

The front end needs to display data that is aggregated from multiple
tables via SQL server views. The views already exist in the database
and are sufficiently complex that I cannot consider recoding them
using business objects etc.

Is it possible to use a SQL Server view as the source for an Active
Record - I want to create a form that displays the aggregrated data
(represented by views). There in no requirement to update from these
views.

Any links/references/examples/tutorials would be helpful.

TIA,
BrendanC


#2

On 23/03/07, BrendanC removed_email_address@domain.invalid wrote:

Is it possible to use a SQL Server view as the source for an Active
Record - I want to create a form that displays the aggregrated data
(represented by views). There in no requirement to update from these
views.

I do this all the time without any problems. Simply access the view
as though it were a table.

Tom


#3

Hi,

I use this and it works fine.

2007/3/23, BrendanC removed_email_address@domain.invalid:

using business objects etc.
BrendanC


Weverton G. de Morais
Tecnólogo em Redes de Comunicação
Desenvolvedor Delphi


#4

I do this all the time without any problems. Simply access
the view as though it were a table.

I do this for aggregate statistics views by choosing the model most
closely tied to the view and calling find_by_sql on its class. Is there
a benefit to actually making model objects for the views? How do you
cope with views that do not have primary keys? Alternately, is there a
benefit to getting the DBI connection and calling query manually instead
of going through find_by_sql?

  • donald

#5

On 23/03/07, Ball, Donald A Jr (Library) removed_email_address@domain.invalid
wrote:

I do this all the time without any problems. Simply access
the view as though it were a table.

I do this for aggregate statistics views by choosing the model most
closely tied to the view and calling find_by_sql on its class. Is there
a benefit to actually making model objects for the views? How do you
cope with views that do not have primary keys?

As long as you’re not doing updates, the lack of primary keys isn’t an
issue. Using a model object gives the adapter the opportunity to type
cast the returned values consistently. It also makes it easier to
auto-generate aggregate queries (avoiding find_by_sql). As an
example, I use a plugin that allows
SalaryReport.group_by(:department_id) and similar. I can share if
you’re interested.

Tom


#6

On 26/03/07, Weverton G. removed_email_address@domain.invalid wrote:

What’s plugin’s name?? I want it.

I’m not able to officially release it as I don’t have the time to
support it. I can provide the (very scrappy) code if you want to play
around with it, at your own risk! Usage is pretty basic. First,
define model with some aggregates:

class SalaryReport < ActiveRecord::Base
self.aggregates = {
:salary => ‘sum(salary)’,
:average_salary => ‘avg(salary)’
}
end

Then, call group_by(columns) to get something you can turn into a
report:

SalaryReport.group_by(:country_id, :department_id)

It will select all the aggregated columns you’ve defined, as well as
the grouped attributes, so the example above is similar to

SELECT country_id, department_id, sum(salary) salary. avg(salary)
average_salary
FROM salary_report
GROUP BY country_id, department_id

You can also include conditions if you wish, similar to those for the
find method:

SalaryReport.group_by(:country_id, :conditions => {:region_id =>
‘EUROPE’})

Here’s the actual code:

module Tomafro::ActiveRecord::GroupBy
def self.included(base)
base.extend(ClassMethods)
end

module ClassMethods
def group_by(*groups)
groups = groups.dup.flatten
options = groups.last.is_a?(Hash) ? groups.pop : {}
scope = scope(:find)
aggregate_columns = self.aggregates.collect do |key, value|
“#{value} #{key}”
end
group_columns = groups.collect(&:to_s)
sql = “SELECT #{(group_columns + aggregate_columns).join(”,\n “)}
"
sql << “FROM #{table_name} "
add_conditions!(sql, options[:conditions], scope)
sql << " GROUP BY #{group_columns.join(”, “)}”
sql << " WITH ROLLUP” if options[:rollup]
records = find_by_sql(sql)
records.each { |record| record.readonly! }
records
end

def aggregates
  @aggregates || {}
end

def aggregates=(aggregates)
  @aggregates = aggregates
end

end
end

ActiveRecord::Base.send(:include, Tomafro::ActiveRecord::GroupBy)


#7

On Mar 26, 2007, at 8:27 AM, Tom W. wrote:

self.aggregates = {
It will select all the aggregated columns you’ve defined, as well as
SalaryReport.group_by(:country_id, :conditions => {:region_id =>
def group_by(*groups)
add_conditions!(sql, options[:conditions], scope)

def aggregates=(aggregates)
  @aggregates = aggregates
end

end
end

ActiveRecord::Base.send(:include, Tomafro::ActiveRecord::GroupBy)

I just read about ActiveRecord::Calculations::ClassMethods this
morning. Tom, do the grouping capabilities provided by those methods
not meet your needs such that you wrote this plugin for yourself?

Thanks,
Craig


#8

What’s plugin’s name?? I want it.

2007/3/26, Tom W. removed_email_address@domain.invalid:

a benefit to actually making model objects for the views? How do you
Tom


Weverton G. de Morais
Tecnólogo em Redes de Comunicação
Desenvolvedor Delphi


#9

I just read about ActiveRecord::Calculations::ClassMethods this
morning. Tom, do the grouping capabilities provided by those methods
not meet your needs such that you wrote this plugin for yourself?

Last I looked, the Calculations stuff could only pull out a single
aggregate at a time. i.e to find total payroll and average salary
would take two queries:

SalaryReport.sum(:salary, :conditions => {:country_id => ‘DE’})
SalaryReport.avg(:salary, :conditions => {:country_id => ‘DE’})

Of course, it’s also possible to get these results using the standard
finder:

SalaryReport.find(:all, :select => ‘sum(salary) total_salary,
avg(salary) avg_salary’ …)

I’m not advocating my code over either of these techniques. For my
particular purpose, where I’m pulling several reports down from views,
each of which can be grouped in an astounding number of ways, my
little piece of code has proved useful. For general grouping code,
you may well find the existing finder methods sufficient.

Tom