skunk

package skunk

Skunk is a functional data access layer for Postgres.

Design principles:

Skunk doesn't use JDBC. It speaks the Postgres wire protocol. It will not work with any other database back end.
Skunk is asynchronous all the way down, via cats-effect, fs2, and ultimately nio. The high-level network layers (Protocol and Session) are safe to use concurrently.
Serialization to and from schema types is not typeclass-based, so there are no implicit derivations. Codecs are explicit, like parser combinators.
I'm not sweating arity abstraction that much. Pass a ~ b ~ c for three args and Void if there are no args. This may change in the future but it's fine for now.
Skunk uses Resource for lifetime-managed objects, which means it takes some discipline to avoid leaks, especially when working concurrently. May or may not end up being problematic.
I'm trying to write good Scaladoc this time.

A minimal example follows. We construct a Resource that yields a Session, then use it.

package example

import cats.effect._
import skunk._
import skunk.implicits._
import skunk.codec.numeric._

object Minimal extends IOApp {

 val session: Resource[IO, Session[IO]] =
   Session.single(
     host     = "localhost",
     port     = 5432,
     user     = "postgres",
     database = "world",
   )

 def run(args: List[String]): IO[ExitCode] =
   session.use { s =>
     for {
       n <- s.unique(sql"select 42".query(int4))
       _ <- IO(println(s"The answer is $n."))
     } yield ExitCode.Success
   }

}

Continue reading for an overview of the library. It's pretty small.

Attributes

Members list

Packages

Skunk network stack, starting with BitVectorSocket at the bottom and ending with Protocol at the top (Session delegates all its work to Protocol).

Skunk network stack, starting with BitVectorSocket at the bottom and ending with Protocol at the top (Session delegates all its work to Protocol). Everything is non-blocking.

Attributes

Grouped members

Queries and Commands

Skunk recognizes two classes of statements: Query, for statements that return rows; and Command, for statements that do not return rows. These values can be constructed directly but typically arise via the sql interpolator.

val q = sql"""
  SELECT id, name
  FROM   employee
  WHERE  age > $int2
""".query(int4 ~ varchar) // Query[Short, Long ~ String]

In the above example note that query parameters are specified by interpolated Encoders and column types are specified by a Decoder passed to .query. The ~ syntax constructs left-associated HLists of types and values via nested pairs. These are all described in more detail a bit further down. Commands are constructed in a similar way but have no output columns and thus no Decoder is needed.

val c = sql"""
  UPDATE employee
  SET    salary = salary * 1.05
  WHERE  id = $int8
""".command // Command[Long]

The interpolator also permits nested Fragments and interpolated constants like table names. See StringContextOps for more information on the interpolator.

SQL and parameter encoder for a statement that returns no rows.

SQL and parameter encoder for a statement that returns no rows. We assume that sql has the same number of placeholders of the form $1, $2, etc., as the number of slots encoded by encoder, and that the parameter types specified by encoder are consistent with the schema. The check methods on Session provide a means to verify this assumption.

You can construct a Command directly, although it is more typical to use the sql interpolator.

sql"INSERT INTO foo VALUES ($int2, $varchar)".command // Command[(Short, String)]

Value parameters

encoder: An encoder for all parameters $1, $2, etc., in sql.
sql: A SQL statement returning no rows.

Attributes

See also: StringContextOps for information on the sql interpolator.

Session for information on executing a Command.
Companion: object
Source: Command.scala
Supertypes: trait Serializable

trait Product

trait Equals

trait Statement[A]

class Object

trait Matchable

class Any
Show all

A composable, embeddable hunk of SQL and typed parameters (common precursor to Command and Query).

A composable, embeddable hunk of SQL and typed parameters (common precursor to Command and Query). Although it is possible to construct a Fragment directly it is more typical to use the sql interpolator.

Attributes

Companion: object
Source: Fragment.scala
Supertypes: trait Serializable

trait Product

trait Equals

trait A => AppliedFragment

class Object

trait Matchable

class Any
Show all

SQL, parameter encoder, and row decoder for a statement that returns rows.

SQL, parameter encoder, and row decoder for a statement that returns rows. We assume that sql has the same number of placeholders of the form $1, $2, etc., as the number of slots encoded by encoder, that sql selects the same number of columns are the number of slots decoded by decoder, and that the parameter and column types specified by encoder and decoder are consistent with the schema. The check methods on Session provide a means to verify this assumption.

You can construct a Query directly, although it is more typical to use the sql interpolator.

sql"SELECT name, age FROM person WHERE age > $int2".query(varchar *: int2) // Query[Short, (String, Short)]

Value parameters

decoder: A decoder for selected columns.
encoder: An encoder for all parameters $1, $2, etc., in sql.
origin: The Origin where the sql was defined, if any.
sql: A SQL statement returning no rows.

Attributes

See also: StringContextOps for information on the sql interpolator.

Session for information on executing a Query.
Companion: object
Source: Query.scala
Supertypes: trait Serializable

trait Product

trait Equals

trait Statement[A]

class Object

trait Matchable

class Any
Show all

Session Values

Skunk's central abstraction is the Session, which represents a connection to Postgres. From the Session we can produce prepared statements, cursors, and other resources that ultimately depend on their originating Session.

A channel that can be used for inter-process communication, implemented in terms of LISTEN and NOTIFY.

A channel that can be used for inter-process communication, implemented in terms of LISTEN and NOTIFY. All instances start life as a Channel[F, String, Notification] but can be mapped out to different input and output types. See the linked documentation for more information on the transactional semantics of these operations.

Attributes

See also: LISTEN

NOTIFY
Companion: object
Source: Channel.scala
Supertypes: trait Stream[F, A] => Stream[F, Unit]

class Object

trait Matchable

class Any
Self type: Channel[F, A, B]

An open cursor from which rows can be fetched, valid during the lifetime its defining Session.

An open cursor from which rows can be fetched, valid during the lifetime its defining Session. You can use this mechanism to implement chunked reads and paged results, although it is ofen more pleasant to use a Cursor-backed Stream, as produced by PreparedQuery#stream.

Attributes

Companion: object
Source: Cursor.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Cursor[F, A]

A prepared command, valid for the life of its defining Session.

Attributes

Companion: object
Source: PreparedCommand.scala
Supertypes: class Object

trait Matchable

class Any
Self type: PreparedCommand[F, A]

A prepared query, valid for the life of its originating Session.

Attributes

Companion: object
Source: PreparedQuery.scala
Supertypes: class Object

trait Matchable

class Any

Represents a live connection to a Postgres database.

Represents a live connection to a Postgres database. Operations provided here are safe to use concurrently. Note that this is a lifetime-managed resource and as such is invalid outside the scope of its owning Resource, as are any streams constructed here. If you start an operation be sure to join its Fiber before releasing the resource.

See the companion object for information on obtaining a pooled or single-use instance.

Attributes

Companion: object
Source: Session.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: class Impl[F]

Codecs

When you construct a statement each parameter is specified via an Encoder, and row data is specified via a Decoder. In some cases encoders and decoders are symmetric and are defined together, as a Codec. There are many variants of this pattern in functional Scala libraries; this is closest in spirit to the strategy adopted by scodec.

Symmetric encoder and decoder of Postgres text-format data to and from Scala types.

Attributes

Companion: object
Source: Codec.scala
Supertypes: trait Decoder[A]

trait Encoder[A]

class Object

trait Matchable

class Any
Self type: Codec[A]

Decoder of Postgres text-format data into Scala types.

Attributes

Companion: object
Source: Decoder.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: trait Codec[A]
Self type: Decoder[A]

Encoder of Postgres text-format data from Scala types.

Attributes

Companion: object
Source: Encoder.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: trait Codec[A]
Self type: Encoder[A]

A singly-inhabited type representing arguments to a parameterless statement.

Attributes

Companion: object
Source: Void.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: object Void.type

HLists

This idea was borrowed from scodec. We use ~ to build left-associated nested pairs of values and types, and can destructure with ~ the same way.

val a: Int ~ String ~ Boolean =
  1 ~ "foo" ~ true
a match {
  case n ~ s ~ b => ...
}

Note that the ~ operation for Codec, Encoder, and Decoder is lifted. This is usually what you want. If you do need an HList of encoders you can use Tuple2.

val c: Encoder[Int ~ String ~ Boolean]
  int4 ~ bpchar ~ bit
// Unusual, but for completeness you can do it thus:
val d: Encoder[Int] ~ Encoder[String] ~ Encoder[Boolean] =
  ((int4, bpchar), bit)

It is possible that we will end up switching to shapeless.HList but this is good for now.

Companion providing unapply for ~ such that (x ~ y ~ z) match { case a ~ b ~ c => ... }.

Attributes

Source: package.scala
Supertypes: class Object

trait Matchable

class Any
Self type: ~.type

Infix alias for (A, B) that provides convenient syntax for left-associated HLists.

Attributes

Source: package.scala

Companion Objects

Companion objects for the traits and classes above.

Attributes

Companion: trait
Source: Channel.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Channel.type

Attributes

Companion: trait
Source: Codec.scala
Supertypes: trait TwiddleSyntax[Codec]

class Object

trait Matchable

class Any
Self type: Codec.type

Attributes

Companion: class
Source: Command.scala
Supertypes: trait Product

trait Mirror

class Object

trait Matchable

class Any
Self type: Command.type

Attributes

Companion: trait
Source: Cursor.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Cursor.type

Attributes

Companion: trait
Source: Decoder.scala
Supertypes: trait TwiddleSyntax[Decoder]

class Object

trait Matchable

class Any
Self type: Decoder.type

Attributes

Companion: trait
Source: Encoder.scala
Supertypes: trait TwiddleSyntax[Encoder]

class Object

trait Matchable

class Any
Self type: Encoder.type

Attributes

Companion: class
Source: Fragment.scala
Supertypes: trait Product

trait Mirror

trait TwiddleSyntax[Fragment]

class Object

trait Matchable

class Any
Show all
Self type: Fragment.type

Attributes

Companion: trait
Source: PreparedCommand.scala
Supertypes: class Object

trait Matchable

class Any
Self type: PreparedCommand.type

Attributes

Companion: trait
Source: PreparedQuery.scala
Supertypes: class Object

trait Matchable

class Any
Self type: PreparedQuery.type

Attributes

Companion: class
Source: Query.scala
Supertypes: trait Product

trait Mirror

class Object

trait Matchable

class Any
Self type: Query.type

Attributes

Companion: trait
Source: Session.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Session.type

Attributes

Companion: trait
Source: Void.scala
Supertypes: trait Singleton

trait Product

trait Mirror

trait Serializable

trait Product

trait Equals

trait Void

class Object

trait Matchable

class Any
Show all
Self type: Void.type

Type members

Classlikes

A fragment applied to its argument, yielding an existentially-typed fragment + argument pair that can be useful when constructing dynamic queries in application code.

A fragment applied to its argument, yielding an existentially-typed fragment + argument pair that can be useful when constructing dynamic queries in application code. Applied fragments must be deconstructed in order to prepare and execute.

Attributes

Companion: object
Source: AppliedFragment.scala
Supertypes: class Object

trait Matchable

class Any
Self type: AppliedFragment

Attributes

Companion: trait
Source: AppliedFragment.scala
Supertypes: class Object

trait Matchable

class Any
Self type: AppliedFragment.type

Specifies how encoded values are redacted before being shown in exceptions and traces.

Attributes

Companion: object
Source: RedactionStrategy.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: object All.type

object None.type

object OptIn.type

Attributes

Companion: trait
Source: RedactionStrategy.scala
Supertypes: trait Sum

trait Mirror

class Object

trait Matchable

class Any
Self type: RedactionStrategy.type

Attributes

Companion: object
Source: SSL.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: object None.type

object System.type

object Trusted.type
Self type: SSL

Attributes

Companion: class
Source: SSL.scala
Supertypes: class Object

trait Matchable

class Any
Self type: SSL.type

Enumerated type of Postgres error codes.

Enumerated type of Postgres error codes. These can be used as extractors for error handling, for example:

doSomething.recoverWith { case SqlState.ForeignKeyViolation(ex) => ... }

Attributes

See also: PostgreSQL Error Codes
Source: SqlState.scala
Supertypes: trait Enum

trait Serializable

trait Product

trait Equals

class Object

trait Matchable

class Any
Show all

Attributes

Companion: object
Source: Statement.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: class Command[A]

class Query[A, B]

Attributes

Companion: trait
Source: Statement.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Statement.type

Control methods for use within a transaction block.

Control methods for use within a transaction block. An instance is provided when you call Session.transaction(...).use.

Attributes

See also: Session#transaction for information on default commit/rollback behavior
Companion: object
Source: Transaction.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Transaction[F]

Attributes

Companion: trait
Source: Transaction.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Transaction.type

Attributes

Source: feature.scala
Supertypes: class Object

trait Matchable

class Any
Self type: feature.type

Attributes

Source: feature.scala
Supertypes: class Object

trait Matchable

class Any
Self type: featureFlags.type

Attributes

Source: package.scala
Supertypes: trait ToAllOps

trait ToDecoderOps

trait ToDecoderOpsLow

trait ToEncoderOps

trait ToEncoderOpsLow

trait ToCodecOps

trait ToCodecOpsLow

trait ToListOps

trait ToStringContextOps

trait ToIdOps

class Object

trait Matchable

class Any
Show all
Self type: implicits.type

Types

Attributes

Source: package.scala

Attributes

Source: package.scala

Value members

Concrete fields

Attributes

Source: package.scala

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