Copy model data between databases

Update: I have modified the task to use save_with_valdation(false) and made it available
as a download here.

------------------


This is an update on the post I made yesterday about how easy it is to copy model data between production and development databases.

The problem with the approach mentioned here is that the id of the original model data is not preserved. As a result, if you copy models with relationships defined using foreign keys, the relationships are not maintained.

I found that instead of using [model].create, I can use [model].new and then set the id explicitly.

model_data.each do |m|
new = model_data.new m.attributes
new.id = m.id
new.save!
end

I wrote up a rake task to do something like

rake db:cloneModelData MODEL=User,Account BATCH=Y

And the task is

namespace :db do
desc "Clone the data associated with a model from the production database to the development database.\n\n" +
" # If the development database contains any data related to the model, it is purged before the copy is made.\n" +
" # Specify the model class name on the command line as MODEL=X,Y,Z (no spaces)\n" +
" # Source database as SOURCE=db (production by default)\n" +
" # Destination database as DESTINATION=db (development by default)\n\n" +
" # To enable batch mode BATCH=Y (By default, the task queries the user to view the yaml and \n" +
" # write it to a file (just in case-call me chicken if you wish)\n" +
" # e.g. rake db:cloneModelData MODEL=User,Account,Post BATCH=Y\n"
task :cloneModelData => :environment do

batchmode = ENV['BATCH'] ? ENV['BATCH'] =~ /^y$/i : false
sourcedb = ENV['SOURCE'] || 'production'
puts "Connecting to source database '#{sourcedb}'"
ActiveRecord::Base.establish_connection(sourcedb)

unless ENV['MODEL']
print "Please specify the model class name(s) seperated by commas: "
model_names = $stdin.gets.strip
else
model_names = ENV['MODEL'].strip
end

data = {}
model_names.split(/,/).each do |model_name|

begin
klass = Kernel.const_get model_name
rescue
raise "Hmm unable to get a Class object corresponding to #{model_name}. Check if you specified the correct model name: #{$!}"
end

unless klass.superclass == ActiveRecord::Base
raise "#{model_name}.superclass (#{klass.superclass}) is not ActiveRecord::Base"
end

puts "\nCollecting data for Model Class - #{model_name}"

# Collect all the data from te production database
data[model_name] = klass.find(:all)
puts "Found #{data[model_name].length} records in the #{sourcedb} database"

unless batchmode
print "\nDo you want to see a yaml dump? [y|N]: "
if $stdin.gets.strip =~ /^y/i
puts data[model_name].to_yaml
end
print "\nDo you want to direct the yaml dump to a file? [Y|n]: "
unless $stdin.gets.strip =~ /^n/i
print "\nPlease specify the file name : "
File.open($stdin.gets.strip, 'w') do |f|
f.write data[model_name].to_yaml
end
end
end

end

destdb = ENV['DESTINATION'] || 'development'
puts "\n--------------------------------------\n\nEstablising connection with the '#{destdb}' database\n\n"

ActiveRecord::Base.establish_connection(destdb)

puts "Now deleting model related data from the #{destdb} db\n"

data.keys.each do |model_name|

klass = Kernel.const_get model_name

olddata = klass.find(:all)

puts "\nFound #{olddata.length} #{model_name} records in the #{destdb} database"
unless batchmode
print "Do you want to see a yaml dump? [y|N]: "
if $stdin.gets.strip =~ /^y/i
puts olddata.to_yaml
end
end

puts "Deleting old data"
olddata.each {|f| f.destroy}

puts "Now copying the #{sourcedb} model data into the #{destdb} database"
print "Copying #{model_name} records: "
i = 0
data[model_name].each do |d|
begin
print "#{ i+=1}, "

obj = klass.new d.attributes
obj.id = d.id
obj.save!

#klass.reflect_on_all_associations.each { |a|
# puts classname + " -> " + a.name.to_s.camelize.singularize + " [label="+a.macro.to_s+"]"
#}

rescue
raise "Error saving model data: #{$!}"
end
end
puts "\nDone copying #{model_name}\n"
end
puts "\nDone."

end
end

Njoy!