Skull - Swift SQLite

Everything should be made as simple as possible, but no simpler.
—Albert Einstein

The Skull Swift package offers a bare bones (400 LOC) interface for SQLite. Emphasising simplicity, its synchronous API implements a minimal set of functions for interacting with SQLite.

import Foundation
import Skull

let skull: DispatchQueue = DispatchQueue(label: "ink.codes.skull")
let db = skull.sync {
  return try! Skull()
}

skull.async {
  let sql = "create table planets (id integer primary key, au double, name text);"

  try! db.exec(sql)
}

skull.async {
  let sql = "insert into planets values (?, ?, ?);"

  try! db.update(sql, 0, 0.4, "Mercury")
  try! db.update(sql, 1, 0.7, "Venus")
  try! db.update(sql, 2, 1, "Earth")
  try! db.update(sql, 3, 1.5, "Mars")
}

skull.sync {
  let sql = "select name from planets where au=1;"

  try! db.query(sql) { er, row in
    assert(er == nil)

    let name = row?["name"] as! String

    assert(name == "Earth")
    print(name)

    return 0
  }
}

Skull is deliberately thin, its tiny API leaves access serialization to users. Leveraging a dedicated serial queue, as shown in the example above, intuitively ensures serialized access.

enum SkullError: Error

SkullError enumerates explicit errors.

• alreadyOpen(String)
• failedToFinalize(Array<Error>)
• invalidURL
• notOpen
• sqliteError(Int, String)
• sqliteMessage(String)
• unsupportedType

typealias SkullRow = Dictionary<String, Any>

SkullRow models a row within a SQLite table. Being a Dictionary, it offers subscript access to column values, which can be of three essential types:

• String
• Int
• Double

For example:

row["a"] as String == "500.0"
row["b"] as Int == 500
row["c"] as Double == 500.0

class Skull: SQLDatabase

Skull, the main object of this module, represents a SQLite database connection. It adopts the SQLDatabase protocol, which defines its interface:

protocol SQLDatabase {
  var url: URL? { get }

  func flush() throws
  func exec(_ sql: String, cb: @escaping (SkullError?, [String : String]) -> Int) throws
  func query(_ sql: String, cb: (SkullError?, SkullRow?) -> Int) throws
  func update(_ sql: String, _ params: Any?...) throws
}

To open a database connection you initialize a new Skull object.

init(_ url: URL? = nil) throws

• url The location of the database file to open.

Opens the database located at file url. If the file does not exist, it is created. Skipping url or passing nil opens an in-memory database.

A Skull object, representing a database connection, offers following methods for accessing the database.

func exec(sql: String, cb: ((SkullError?, [String:String]) -> Int)?)) throws

• sql Zero or more UTF-8 encoded, semicolon-separated SQL statements.
• cb A callback to handle results or abort by returning non-zero.

Executes SQL statements and applies the callback for each result, limited to strings in this case. The callback is optional, if provided, it can abort execution by returning non-zero. The callback doesn't just handle results, it can also monitor execution and, if need be, abort the operation; it is applied zero or more times.

func query(sql: String, cb: (SkullError?, SkullRow?) -> Int) throws

• sql The SQL statement to query the database with.
• cb The callback to handle resuting errors and rows.

Queries the database with the specified selective SQL statement and applies the callback for each resulting row or occuring error.

func update(sql: String, params: Any?...) throws

• sql The SQL statement to apply.
• params The parameters to bind to the statement.

Updates the database by binding the specified parameters to an SQLite statement, for example:

let sql = "insert into planets values (?, ?, ?);"
try! db.update(sql, 0, 0.4, "Mercury")

This method may throw SkullError.sqliteError(Int, String) or SkullError.unsupportedType.

func flush() throws

Removes and finalizes all cached prepared statements.

var url: URL? { get }

The location of the database file.

Close the database by simply dismissing the Skull object.

📦 Add https://github.com/michaelnisi/skull to your package manifest.

MIT