Prepared statements

Prepared statements are used to prepare a write query only once and execute it multiple times with different values. A bind variable marker ? is used to represent a dynamic value in a statement.

an INSERT statement is prepared

Given

a running cassandra cluster with schema:

CREATE KEYSPACE simplex WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 3};
USE simplex;
CREATE TABLE playlists (
  id uuid,
  title text,
  album text,
  artist text,
  song_id uuid,
  PRIMARY KEY (id, title, album, artist)
);

And

the following example:

require 'cassandra'

cluster = Cassandra.cluster
session = cluster.connect("simplex")
insert  = session.prepare(
            "INSERT INTO playlists (id, song_id, title, artist, album) " \
            "VALUES (62c36092-82a1-3a00-93d1-46196ee77204, ?, ?, ?, ?)"
          )

songs = [
  {
    :id     => Cassandra::Uuid.new('756716f7-2e54-4715-9f00-91dcbea6cf50'),
    :title  => 'La Petite Tonkinoise',
    :album  => 'Bye Bye Blackbird',
    :artist => 'Joséphine Baker'
  },
  {
    :id     => Cassandra::Uuid.new('f6071e72-48ec-4fcb-bf3e-379c8a696488'),
    :title  => 'Die Mösch',
    :album  => 'In Gold',
    :artist => 'Willi Ostermann'
  },
  {
    :id     => Cassandra::Uuid.new('fbdf82ed-0063-4796-9c7c-a3d4f47b4b25'),
    :title  => 'Memo From Turner',
    :album  => 'Performance',
    :artist => 'Mick Jager'
  },
]

songs.each do |song|
  session.execute(insert, song[:id], song[:title], song[:artist], song[:album])
end

session.execute("SELECT * FROM playlists").each do |row|
  $stderr.puts("#{row["artist"]}: #{row["title"]} / #{row["album"]}")
end

When

it is executed

Then

its output should contain:

Joséphine Baker: La Petite Tonkinoise / Bye Bye Blackbird

And

its output should contain:

Willi Ostermann: Die Mösch / In Gold

And

its output should contain:

Mick Jager: Memo From Turner / Performance

a SELECT statement with parameterized LIMIT is prepared

Given

a running cassandra cluster with schema:

CREATE KEYSPACE simplex WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 3};
USE simplex;
CREATE TABLE playlists (
  id uuid,
  title text,
  album text,
  artist text,
  song_id uuid,
  PRIMARY KEY (id, title, album, artist)
);
INSERT INTO playlists (id, song_id, title, album, artist)
VALUES (
   2cc9ccb7-6221-4ccb-8387-f22b6a1b354d,
   756716f7-2e54-4715-9f00-91dcbea6cf50,
   'La Petite Tonkinoise',
   'Bye Bye Blackbird',
   'Joséphine Baker'
);
INSERT INTO playlists (id, song_id, title, album, artist)
VALUES (
   2cc9ccb7-6221-4ccb-8387-f22b6a1b354d,
   f6071e72-48ec-4fcb-bf3e-379c8a696488,
   'Die Mösch',
   'In Gold',
   'Willi Ostermann'
);
INSERT INTO playlists (id, song_id, title, album, artist)
VALUES (
   3fd2bedf-a8c8-455a-a462-0cd3a4353c54,
   fbdf82ed-0063-4796-9c7c-a3d4f47b4b25,
   'Memo From Turner',
   'Performance',
   'Mick Jager'
);
INSERT INTO playlists (id, song_id, title, album, artist)
VALUES (
   3fd2bedf-a8c8-455a-a462-0cd3a4353c54,
   756716f7-2e54-4715-9f00-91dcbea6cf50,
   'La Petite Tonkinoise',
   'Bye Bye Blackbird',
   'Joséphine Baker'
);

And

the following example:

require 'cassandra'

cluster = Cassandra.cluster
session = cluster.connect("simplex")
select  = session.prepare("SELECT * FROM playlists LIMIT ?")
limits  = [1, 2, 3]

limits.each do |limit|
  rows = session.execute(select, limit)
  puts "selected #{rows.size} row(s)"
end

When

it is executed

Then

its output should contain:

selected 1 row(s)
selected 2 row(s)
selected 3 row(s)