Sometimes you need to iterate through a table in chunks. It's extremely inefficient to use hand-crafted `LIMIT` and `OFFSET` queries to do this.

PostgreSQL provides built-in functionality to fetch a "cursor" to your results and page through the cursor efficiently fetching chunks of the results with full MVCC compliance.

This actually ends up pairing very nicely with node's _asyncness_ and handling a lot of data. PostgreSQL is rad.

var Cursor = require('pg-cursor')

var pg = require('pg')

pg.connect(function(err, client, done) {

//imagine some_table has 30,000,000 results where prop > 100

//lets create a query cursor to efficiently deal with the huge result set

var cursor = client.query(new Cursor('SELECT * FROM some_table WHERE prop > $1', [100]))

//read the first 100 rows from this cursor

cursor.read(100, function(err, rows) {

if(err) {

//cursor error - release the client

//normally you'd do app-specific error handling here

return done(err)

}

//when the cursor is exhausted and all rows have been returned

//all future calls to `cursor#read` will return an empty row array

//so if we received no rows, release the client and be done

if(!rows.length) return done()

//do something with your rows

//when you're ready, read another chunk from

//your result

cursor.read(2000, function(err, rows) {

//I think you get the picture, yeah?

//if you dont...open an issue - I'd love to help you out!

//Also - you probably want to use some sort of async or promise library to deal with paging

//through your cursor results. node-pg-cursor makes no asumptions for you on that front.

})

})

});

Creates an instance of a query cursor. Pass this instance to node-postgres [`client#query`](https://github.com/brianc/node-postgres/wiki/Client#wiki-method-query-parameterized)

Read `rowCount` rows from the cursor instance. The `callback` will be called when the rows are available, loaded into memory, parsed, and converted to JavaScript types.

If the cursor has read to the end of the result sets all subsequent calls to `cursor#read` will return a 0 length array of rows. I'm open to other ways to signal the end of a cursor, but this has worked out well for me so far.

`result` is a special [https://github.com/brianc/node-postgres/wiki/Query#result-object](Result) object that can be used to accumulate rows.

Closes the backend portal before itterating through the entire result set. Useful when you want to 'abort' out of a read early but continue to use the same client for other queries after the cursor is finished.