import Foundation
import SQLKit

// Information we'll need later.
let (dbURL, userIDs): (URL, [Int]) = ...

// A SQLDatabase represents connection settings to talk to a database.
// (Currently just the client and URL.)
// 
// "PostgreSQL" here is a type conforming to SQLClient. You don't use 
// SQLClients directly, but you can implement one yourself.
// 
// SQL includes an AnySQLClient type which allows your code to 
// dynamically connect to any registered database type.
let db = SQLDatabase<PostgreSQL>(url: dbURL)

// A SQLConnection<PostgreSQL> is an individual connection to the database.
let connection = try db.makeConnection()

// A SQLStatement represents a whole or partial statement. Values interpolated 
// into a SQLStatement will be passed through placeholders or escaped, unless 
// they are themselves SQLStatements.
let whereClause: SQLStatement
if userIDs.isEmpty {
  whereClause = ""
}
else {
  whereClause = "WHERE " + userIDs.map { "id = \($0)" }.joined(" OR ")
}

// Perform the actual query.
let users = try db.query("SELECT * FROM users \(whereClause)")

// A SQLQuery<PostgreSQL> represents the results of an individual query. It 
// is used for two things.
// 
// 1. Get `SQLColumnKey`s representing the columns in the result set:
let idKey = try users.columnKey(forName: "id", as: Int.self)
let nameKey = try users.columnKey(forName: "name", as: String?.self)

// 2. Access the rows through its iterator:
for user in users.rowIterator {
  let id = try user.value(for: idKey)
  let name = try user.value(for: nameKey) ?? "[no name]"
  print("\(id)\t\(name)")
}