Cursors

Docs: find_each_with_cursor, find_in_batches_with_cursor, cursor

Note: This section is only relevant to applications using PostgreSQL.

For batched loading, cursors perform better than the traditional OFFSET & LIMIT approach. If you're using PostgreSQL, take advantage of them with find_each_with_cursor and find_in_batches_with_cursor.

OccamsRecord.
  query(q).
  eager_load(:customer).
  find_each_with_cursor { |order|
    ...
  }

OccamsRecord.
  query(q).
  eager_load(:customer).
  find_in_batches_with_cursor { |orders|
    orders.each { |order| ... }
  }

If you need custom logic when using your cursor, use the lower-level cursor method:

OccamsRecord.
  query(q).
  eager_load(:customer).
  cursor.
  open { |cursor|
    cursor.move(:forward, 300)
    orders = cursor.fetch(:forward, 100)
    orders.each { |order| ... }
  }

The cursor var is an instance of OccamsRecord::Cursor.

Cursors with hand-written SQL

Using cursors with hand-written SQL is a breeze with find_each_with_cursor and find_in_batches_with_cursor.

OccamsRecord.
  sql("
    SELECT * FROM orders
    WHERE order_date > :date
    ORDER BY order_date DESC, id
  ", {
    date: 10.years.ago
  }).
  find_each_with_cursor(batch_size: 1000) { |order|
    ...
  }

And you still have low-level access via cursor:

OccamsRecord.
  sql("
    SELECT * FROM orders
    WHERE order_date > :date
    ORDER BY order_date DESC, id
  ", {
    date: 10.years.ago
  }).
  cursor.
  open { |cursor|
    cursor.move(:forward, 300)
    orders = cursor.fetch(:forward, 100)
    orders.each { |order| ... }
  }