Troy is an open source macro-based Cassandra driver for Scala applications, similar to Slick and Quill, provides type-safe & compile-time checking for database queries. Nevertheless, it doesn't impose a DSL to express the queries in Scala. Instead, it allows developers to write plain Cassandra-query-language (CQL) queries within Scala code, complete with schema validation. In addition, it provides cross-validation against the previous versions, ensuring safe and smooth schema migrations. It is worth noting that Troy doesn't connect to Cassandra during compilation. Instead, the schema is provided as CQL scripts, checked-in within same code base, consisting of plain CREATE TABLE CQL statements. That get's loaded at compile-time into a light-weight Schema engine capable of analysing queries and providing information about column types. Those CQL scripts can be written as increments, by adding new scripts containing ALTER TABLE statement, instead of editing existing scripts. This allows Troy to check backwards and forward compatibility of queries against different versions of the schema. As well as providing tools to write migration scripts.

1. Introducing Troy
Schema-safe Cassandra Toolkit
Tamer AbdulRadi
Senior Software Engineer at Cake Solutions
/tabdulradi
abdulradi.com
/troy/tabdulradi

2. /tabdulradi /tabdulradi /troy
Cassandra
• Distributed NoSQL Database
• Cassandra Query Language

3. /tabdulradi /tabdulradi /troy
Data Modelling
Post Author
Post
authorId K
postId C
postBody
authorName SQueries

4. /tabdulradi /tabdulradi /troy
CQL Shell

5. /tabdulradi /tabdulradi /troy
Java Driver
def listByAuthor(authorId: String) =
session.executeAsync(
"""
SELECT post_id, post_title
FROM test.posts
WHERE author_id = ?
""", authorId)

6. /tabdulradi /tabdulradi /troy
Enter Troy
val listByAuthor = withSchema {
(authorId: String) =>
cql"""
SELECT post_id, post_title
FROM test.posts
WHERE author_id = $authorId;
“""
}

7. /tabdulradi /tabdulradi /troy
Generated Code
val listByAuthor = {
val stmt = session.prepare(
"""SELECT post_id, post_title
FROM test.posts
WHERE author_id = ?""")
(authorId: String) =>
bind(stmt, param(authorId).as[CDT.Text])
}

8. /tabdulradi /tabdulradi /troy
Troy Codec
def param[S](value: S)
def as[C <: CDT](implicit codec: TroyCodec[S, C])

9. /tabdulradi /tabdulradi /troy
Compile-time Registry
TroyCodec[String, CDT.Ascii]
TroyCodec[String, CDT.Text]
TroyCodec[UUID, CDT.Uuid]
TroyCodec[UUID, CDT.TimeUuid]

10. /tabdulradi /tabdulradi /troy
Parsing
case class Post(id: UUID, title: String)
cql"SELECT post_id, post_title FROM test.posts;”
.prepared
.executeAsync
.as(Post)

11. /tabdulradi /tabdulradi /troy
Generated Code
(row: Row) =>
Post(
column[UUID](0)(row).as[CDT.TimeUuid],
column[String](1)(row).as[CDT.Text])

12. /tabdulradi /tabdulradi /troy
Optional Columns
case class Post(
id: UUID,
title: Option[String])
implicit def optionCodec[S, C](
implicit inner: TroyCodec[S, C]):
TroyCodec[Option[S], C]

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Collections
• Seq[S] <—> list<C>
• Set[S] <—> set<C>
• Map[KS, VS] <—> map<KC, VC>

14. /tabdulradi /tabdulradi /troy
Chaining methods
cql"SELECT …"
.prepared
.setConsistencyLevel(QUORUM)
.setFetchSize(100)
.executeAsync
.oneOption
.as(Post)

15. /tabdulradi /tabdulradi /troy
Schema Versioning

16. /tabdulradi /tabdulradi /troy
Schema Versioning

17. /tabdulradi /tabdulradi /troy
Schema Versioning
CREATE KEYSPACE test ...;
CREATE TABLE test.posts (
...
);
resources/schema.cql

18. /tabdulradi /tabdulradi /troy
ALTER TABLE test.posts ADD blah text;
Schema Versioning
resources/schema/01.cql
resources/schema/02.cql
CREATE KEYSPACE test ...;
CREATE TABLE test.posts ( ... );

19. /tabdulradi /tabdulradi /troy
Checked Compatibility
withSchema.minVersion(1) {
(authorId: String) =>
cql"""
SELECT post_id, post_title
FROM test.posts
WHERE author_id = $authorId;
""".prepared.as(Post)
}

20. /tabdulradi /tabdulradi /troy
Road Map
• Release 1.0 by the end
of the year.
• Few missing CQL
features
• Post 1.0
• Shapeless
• New style macro

21. /tabdulradi /tabdulradi /troy
Meta + Paradise
@withSchema def list(authorId: UUID) =
cql"""
SELECT post_id, post_title
FROM test.posts
where author_id = $authorId;
"""
.prepared
.executeAsync
.all
.as[UUID, String, String, Int, Post](Post)

22. /tabdulradi /tabdulradi /troy
Github Contributors