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# Tailable cursors in Ruby
Tailable cursors are cursors that remain open even after they've returned
a final result. This way, if more documents are added to a collection (i.e.,
to the cursor's result set), then you can continue to call `Cursor#next` to
retrieve those results. Here's a complete test case that demonstrates the use
of tailable cursors.
Note that tailable cursors are for capped collections only.
require 'mongo'
require 'test/unit'
class TestTailable < Test::Unit::TestCase
include Mongo
def test_tailable
# Create a connection and capped collection.
@con = Connection.new
@db = @con['test']
@db.drop_collection('log')
@capped = @db.create_collection('log', :capped => true, :size => 1024)
# Insert 10 documents.
10.times do |n|
@capped.insert({:n => n})
end
# Create a tailable cursor that iterates the collection in natural order
@tail = Cursor.new(@capped, :tailable => true, :order => [['$natural', 1]])
# Call Cursor#next 10 times. Each call returns a document.
10.times do
assert @tail.next
end
# But the 11th time, the cursor returns nothing.
assert_nil @tail.next
# Add a document to the capped collection.
@capped.insert({:n => 100})
# Now call Cursor#next again. This will return the just-inserted result.
assert @tail.next
# Close the cursor.
@tail.close
end
end
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109 entries across 63 versions & 3 rubygems