SQLite query results as nodejs readable stream

make_foo_db.sh

echo 'create table foo ( name string, value int )' | sqlite3 foo.db

for idx in {0..1000}
do
echo "insert into foo( name, value ) values( $idx, 'abc${idx}' );"
done | sqlite3 foo.db

SQL query results as nodejs read stream

/*
 *
 *   Return SQLite3 query results as a Nodejs stream, sensitive to backpressure.
 *
 *   Assumes a foo.db file with a lot of rows - I used 1000 with a number & a string
 */

const stream = require('stream');
const sqlite = require('sqlite3');
class DBStream extends stream.Readable {

    constructor( opts ) {
        super( { objectMode: true } );
        this.sql = opts.sql;
        this.db = new sqlite.Database( opts.db );
        this.stmt = this.db.prepare( this.sql );
        this.on( 'end', () => this.stmt.finalize( () => this.db.close() ));
    }

    _read() {

        let strm = this;
        this.stmt.get( function(err,result) {

            // If result is undefined, push null, which will end the stream.
            /* 
             * Should have no backpressure problems, 
             * since _read is only called when the downstream is 
             * ready to fetch data
             */
            err ?
                strm.emit('error', err ) :
                strm.push( result || null);

       })
    }

}

/*
 * simple test
 */
 
stream.pipeline(
    [
        new DBStream( { sql:'select * from foo' } ),
        new stream.Transform( { objectMode: true, transform:( data, enc, cb ) => cb( null, JSON.stringify( data ) ) } ),
        process.stdout
    ],
    err => { err && console.error(err); process.exit(0) }
)

good stuff