[sqlite] Accessing an SQLite Database in Swift

Sometimes, a Swift version of the "SQLite in 5 minutes or less" approach shown on sqlite.org is sufficient. The "5 minutes or less" approach uses sqlite3_exec() which is a convenience wrapper for sqlite3_prepare(), sqlite3_step(), sqlite3_column(), and sqlite3_finalize().

Swift 2.2 can directly support the sqlite3_exec() callback function pointer as either a global, non-instance procedure func or a non-capturing literal closure {}.

Readable typealias

typealias sqlite3 = COpaquePointer
typealias CCharHandle = UnsafeMutablePointer<UnsafeMutablePointer<CChar>>
typealias CCharPointer = UnsafeMutablePointer<CChar>
typealias CVoidPointer = UnsafeMutablePointer<Void>

Callback Approach

func callback(
    resultVoidPointer: CVoidPointer, // void *NotUsed 
    columnCount: CInt,               // int argc
    values: CCharHandle,             // char **argv     
    columns: CCharHandle             // char **azColName
    ) -> CInt {
    for  i in 0 ..< Int(columnCount) {
        guard let value = String.fromCString(values[i]) 
        else { continue }
        guard let column = String.fromCString(columns[i]) 
        else { continue }
        print("\(column) = \(value)")
    }
    return 0 // status ok
}

func sqlQueryCallbackBasic(argc: Int, argv: [String]) -> Int {
    var db: sqlite3 = nil 
    var zErrMsg:CCharPointer = nil
    var rc: Int32 = 0 // result code

    if argc != 3 {
        print(String(format: "ERROR: Usage: %s DATABASE SQL-STATEMENT", argv[0]))
        return 1
    }

    rc = sqlite3_open(argv[1], &db)
    if  rc != 0 {
        print("ERROR: sqlite3_open " + String.fromCString(sqlite3_errmsg(db))! ?? "" )
        sqlite3_close(db)
        return 1
    }

    rc = sqlite3_exec(db, argv[2], callback, nil, &zErrMsg)
    if rc != SQLITE_OK {
        print("ERROR: sqlite3_exec " + String.fromCString(zErrMsg)! ?? "")
        sqlite3_free(zErrMsg)
    }

    sqlite3_close(db)
    return 0
}

Closure Approach

func sqlQueryClosureBasic(argc argc: Int, argv: [String]) -> Int {
    var db: sqlite3 = nil 
    var zErrMsg:CCharPointer = nil
    var rc: Int32 = 0

    if argc != 3 {
        print(String(format: "ERROR: Usage: %s DATABASE SQL-STATEMENT", argv[0]))
        return 1
    }

    rc = sqlite3_open(argv[1], &db)
    if  rc != 0 {
        print("ERROR: sqlite3_open " + String.fromCString(sqlite3_errmsg(db))! ?? "" )
        sqlite3_close(db)
        return 1
    }

    rc = sqlite3_exec(
        db,      // database 
        argv[2], // statement
        {        // callback: non-capturing closure
            resultVoidPointer, columnCount, values, columns in

            for i in 0 ..< Int(columnCount) {
                guard let value = String.fromCString(values[i]) 
                else { continue }
                guard let column = String.fromCString(columns[i]) 
                else { continue }
                print("\(column) = \(value)")
            }
            return 0
        }, 
        nil, 
        &zErrMsg
    )

    if rc != SQLITE_OK {
        let errorMsg = String.fromCString(zErrMsg)! ?? ""
        print("ERROR: sqlite3_exec \(errorMsg)")
        sqlite3_free(zErrMsg)
    }
    sqlite3_close(db)
    return 0
}

To prepare an Xcode project to call a C library such as SQLite, one needs to (1) add a Bridging-Header.h file reference C headers like #import "sqlite3.h", (2) add Bridging-Header.h to Objective-C Bridging Header in project settings, and (3) add libsqlite3.tbd to Link Binary With Library target settings.

The sqlite.org's "SQLite in 5 minutes or less" example is implemented in a Swift Xcode7 project here.