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