A Modern Finagle-Postgresql Client
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README.md

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roc is a modern Finagle Postgresql Client. What's modern? A Client relying on a 6.x + version of Finagle.

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tl;dr

Roc is published to Maven Central, so for the latest stable version add the following to your build:

libraryDependencies ++= Seq(
  "com.github.finagle" %% "roc-core"  % "0.0.4",
  "com.github.finagle" %% "roc-types" % "0.0.4"
)

Roc is under heavy development, so to stay up to with the latest SNAPSHOT version add the following to your build instead:

resolvers += Resolver.sonatypeRepo("snapshots")

libraryDependencies ++= Seq(
  "com.github.finagle"  %% "roc-core" % "0.0.5-SNAPSHOT" changing()
)

Open sbt console and insert the following

scala > :paste
import com.twitter.util.Await
import roc.Postgresql
import roc.postgresql.{Request, Row}

val client = Postgresql.client
  .withUserAndPasswd("username", "password")
  .withDatabase("database")
  .newRichClient("inet!localhost:5432")
val req = new Request("SELECT * FROM STATES;")
val result = Await.result(client.query(req))
result: roc.postgresql.Result = Result(Text('id,23,1)Text('name,25,Alabama)Text('abbrv,1043,AL), Text('id,23,2)...)

Let's turn a Result into all 50 State(s).

import java.time.ZonedDateTime
import roc.types.decoders._

case class State(id: Int, name: String, abbrv: String, insertedAt: ZonedDateTime)
val row2State: (Row) => (State) = (row: Row) => {
  val id = row.get('id).as[Int]
  val name = row.get('name).as[String]
  val abbrv = row.get('abbrv).as[String]
  val insertedAt = row.get('inserted_at).as[TimestampWithTZ]
  State(id, name, abbrv, insertedAt)
}
val states = result.map(row2State).toList
states: List[State] = List(State(1,Alabama,AL,2016-05-10T11:59:13.879709-05:00), State(2,Alaska,AK,2016-05-10T11:59:20.974995-05:00))

If you're into Scaladocs ( I am ), they can be found here.

Tell me about Result

The most important type in Roc is Result, the type returned after a Postgresql query is executed. Result implements Iterable so that it can be viewed as a collection of Rows. The two additional members of Result are:

val result = client.query(new Request("SELECT * FROM FOO;"))

result.columns // all column information returned from the Request
result.completedCommand // a String representation of what happend

Result.completedCommand

  • For an INSERT command, the tag is INSERT oid rows, where rows is the number of rows inserted. oid is the object ID of the inserted row if rows is 1 and the target table has OIDs; otherwise oid is 0.
  • For a DELETE command, the tag is DELETE rows where rows is the number of rows deleted.
  • For an UPDATE command, the tag is UPDATE rows where rows is the number of rows updated.
  • For a SELECT or CREATE TABLE AS command, the tag is SELECT rows where rows is the number of rows retrieved.
  • For a MOVE command, the tag is MOVE rows where rows is the number of rows the cursor's position has been changed by.
  • For a FETCH command, the tag is FETCH rows where rows is the number of rows that have been retrieved from the cursor.

For an UPDATE or INSERT command, a Result will have a length of 0 and no column information, but will always return a completedCommand. From Postgresql's perspective, the fact that the query returns without giving an error is evidence that the command completed successfully, and Roc will adhere to their style, not the JDBC style.

Row

A Row holds a non-zero number of Elements. An Element is the actual value returned at [row][column]. For example, if we were to execute the following:

scala> val req = new Request("SELECT COUNT(*) FROM STATES;")
scala> val result = Await.result(client.query(req))
result: roc.postgresql.Result = Result(Text('count,20,50))

we are given a Result with one Column (with the name of 'count, a FormatCode of Text, and OID of 20), and one Row. To retrieve a value out of that Row, we do the following:

scala> val head = result.head // let's just get the first row
scala> val count = head.get('count)
count: roc.postgresql.Element = Text('count,20,50)

Wait, what exactly is an Element?

Elements

roc-core has an extremely minimal design philosophy. That includes the decoding of actual data. In other words, we'll decode the bytes into the correct format, we'll tell you what that format is, but it's up to you (or another roc module) to go any further. Postgreql returns data in 3 possible formats:

  1. UTF-8 Text
  2. Binary Format (typically Big Endian)
  3. No data is returned for that column ( mean it is a NULL value )

roc-core will decode this data into the given format, but goes no further in the process - it is up to core clients to decide how to procede. Going back to the example above, we see:

scala> val count = head.get('count)
count: roc.postgresql.Element = Text('count,20,50)

This means that Postgresql has returned a column name 'count, in a String format, with a Postgresql Type of Long. String encodings are typically preferred, and almost universally the case unless the column returned is binary data, or if a FETCH command is used to return a CURSOR. An Element has 3 sub-types

  1. Text
  2. Binary
  3. NULL

Yes, we've deliberately introduced a specific NULL type into the system. This allows clients to handle NULL cases in whatever way they see fit.

To get a value out of an Element, you have several options:

scala> val count = head.get('count)
count: roc.postgresql.Element = Text('count,20,50)

scala> count.asString
res4: String = 50

scala> count.asBytes
roc.postgresql.failures$UnsupportedDecodingFailure: Attempted Binary decoding of String column.

If you attempt to get the String of a Binary element, you'll get another UnsupportedDecodingFailure. The two attempts above are short cuts to getting values. The preferred method involves a fold:

def fold[A](fa: String => A, fb: Array[Byte] => A, fc: () => A): A = this match {
  case Text(_, _, value)   => fa(value)
  case Binary(_, _, value) => fb(value)
  case Null(_, _)          => fc()
}

This allows you to handle NULL values in any way you see fit, and makes the decode process typesafe. Both asString and asBytes call fold under the covers.

Finally, there is the ubiquitous parsing / decoding method as[A]:

def as[A](implicit f: ElementDecoder[A]): A = fold(f.textDecoder, f.binaryDecoder, f.nullDecoder)

An ElementDecoder is a TypeClass to allow custom decoding in a more syntax friendly way. See the Scaladocs or gitter for more information.

decoders

The roc-types project defines type aliases from Postgresql => Scala, and includes ElementDecoder instances for those types. The current types include

  • smallint => Short
  • int => Int
  • bigint => Long
  • real => Float
  • double precision => Double
  • char => Char (Note this is a C-Style understanding of a Char, not a UTF Rune)
  • text/CHARACTER VARYING => String
  • bool => Boolean
  • JSON/JSONB => Json (via Jawn)
  • Date => Date = java.time.LocalDate
  • Time => Time = java.time.LocalTime
  • TIME WITH TIME ZONE => TimestampWithTZ = java.time.ZonedDateTime
  • NULL => Option

Optional Decoders

To decode a column that may be NULL, clients should simply use an Option[A] decoder, where A = COLUMN TYPE. Let's add a population column to our states table, of type int.

case class State(id: Int, name: String, abbrv: String, population: Option[Int],
insertedAt: ZonedDateTime)
val row2State: (Row) => (State) = (row: Row) => {
  val id = row.get('id).as[Int]
  val name = row.get('name).as[String]
  val abbrv = row.get('abbrv).as[String]
  val population = row.get('population).as[Int]
  val insertedAt = row.get('inserted_at).as[TimestampWithTZ]
  State(id, name, abbrv, population, insertedAt)
}
val state = result.map(row2State).toList.head
states: State = State(1,Alabama,AL,None,2016-05-10T12:46:59.998788-05:00)

As the type of column should be known at compile time, roc-types throws an NullDecodedFailure(TYPE) with a helpful error message if you attempt to decode a NULL type:

scala> val row = result.head
row: roc.postgresql.Row = Text('inserted_at,1184,2016-05-1012:46:59.998788-05)Null('population,23)Text('abbrv,1043,AL)Text('name,25,Alabama)Text('id,23,1)
scala> val population = row.get('population).as[Int]
roc.types.failures$NullDecodedFailure: A NULL value was decoded for type INT. Hint: use the Option[INT] decoder, or ensure that Postgres cannot return NULL for the requested value.

Design Philosophy

The desire of core is to be as minimal as possible. In practice, that means mapping a Finagle Service over Postgresql with as little bedazzling as possible. The Postgresql Client will be very minimalistic ( currently just one method, def query(Request): Future[Result]), and the aim is for Result to do as little as possible. Additional future modules may provide additional functionality.

Motivation

The current finagle-postgres was developed pre Finagle 6.x and does not use modern finagle abstractions. These are core enough to require what amounts to a complete rewrite of the driver.

What's in a name?

roc (Rokh or Rukh) is named after the Persian mythological bird of prey Roc, which was based in part on the now extinct elephant bird. Yes, that means we've hit the rare 4 point play with the name

Goal Status
short name ✔️
obligatory mythological reference ✔️
bird reference for Twitter ✔️
elephant reference for Postgresql ✔️

High fives for everyone! Teenage Mutant Ninja Turtles High Fives

Contributors and Participation

roc is currently maintained by Jeffrey Davis.

The roc project supports the Typelevel code of conduct and wants all of its channels (GitHub, gitter, etc.) to be welcoming environments for everyone.

License

Licensed under the BSD-3-Clause (Revised BSD Liscense); you may not use this software except in compliance with the License.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.