DuckDB has a Swift client. See the announcement post for details.
Instantiating DuckDB
DuckDB supports both in-memory and persistent databases. To work with an in-memory datatabase, run:
let database = try Database(store: .inMemory) To work with a persistent database, run:
let database = try Database(store: .file(at: "test.db")) Queries can be issued through a database connection.
let connection = try database.connect() DuckDB supports multiple connections per database.
Application Example
The rest of the page is based on the example of our announcement post, which uses raw data from NASA's Exoplanet Archive loaded directly into DuckDB.
Creating an Application-Specific Type
We first create an application-specific type that we'll use to house our database and connection and through which we'll eventually define our app-specific queries.
import DuckDB final class ExoplanetStore { let database: Database let connection: Connection init(database: Database, connection: Connection) { self.database = database self.connection = connection } } Loading a CSV File
We load the data from NASA's Exoplanet Archive:
wget https://exoplanetarchive.ipac.caltech.edu/TAP/sync?query=select+pl_name+,+disc_year+from+pscomppars&format=csv -O downloaded_exoplanets.csv Once we have our CSV downloaded locally, we can use the following SQL command to load it as a new table to DuckDB:
CREATE TABLE exoplanets AS SELECT * FROM read_csv('downloaded_exoplanets.csv'); Let's package this up as a new asynchronous factory method on our ExoplanetStore type:
import DuckDB import Foundation final class ExoplanetStore { // Factory method to create and prepare a new ExoplanetStore static func create() async throws -> ExoplanetStore { // Create our database and connection as described above let database = try Database(store: .inMemory) let connection = try database.connect() // Download the CSV from the exoplanet archive let (csvFileURL, _) = try await URLSession.shared.download( from: URL(string: "https://exoplanetarchive.ipac.caltech.edu/TAP/sync?query=select+pl_name+,+disc_year+from+pscomppars&format=csv")!) // Issue our first query to DuckDB try connection.execute(""" CREATE TABLE exoplanets AS SELECT * FROM read_csv('\(csvFileURL.path)'); """) // Create our pre-populated ExoplanetStore instance return ExoplanetStore( database: database, connection: connection ) } // Let's make the initializer we defined previously // private. This prevents anyone accidentally instantiating // the store without having pre-loaded our Exoplanet CSV // into the database private init(database: Database, connection: Connection) { ... } } Querying the Database
The following example queires DuckDB from within Swift via an async function. This means the callee won't be blocked while the query is executing. We'll then cast the result columns to Swift native types using DuckDB's ResultSet cast(to:) family of methods, before finally wrapping them up in a DataFrame from the TabularData framework.
... import TabularData extension ExoplanetStore { // Retrieves the number of exoplanets discovered by year func groupedByDiscoveryYear() async throws -> DataFrame { // Issue the query we described above let result = try connection.query(""" SELECT disc_year, count(disc_year) AS Count FROM exoplanets GROUP BY disc_year ORDER BY disc_year """) // Cast our DuckDB columns to their native Swift // equivalent types let discoveryYearColumn = result[0].cast(to: Int.self) let countColumn = result[1].cast(to: Int.self) // Use our DuckDB columns to instantiate TabularData // columns and populate a TabularData DataFrame return DataFrame(columns: [ TabularData.Column(discoveryYearColumn).eraseToAnyColumn(), TabularData.Column(countColumn).eraseToAnyColumn(), ]) } } Complete Project
For the complete example project, clone the DuckDB Swift repository and open up the runnable app project located in Examples/SwiftUI/ExoplanetExplorer.xcodeproj.
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