为什么将数据保存到 SQLite 数据库不适用于 Swift 2？

Question

我正在使用SQLite.swift，我正在使用 SQLite.swift 演示中的这些代码。

import UIKit
import SQLite

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let db = try! Connection()
        let users = Table("users")
        let id = Expression<Int64>("id")
        let email = Expression<String>("email")
        let name = Expression<String?>("name")
        try! db.run(users.create { t in
            t.column(id, primaryKey: true)
            t.column(email, unique: true, check: email.like("%@%"))
            t.column(name)
        })
        try! db.run(users.insert(email <- "alice@mac.com"))
        for user in db.prepare(users) {
            print("id: \(user[id]), email: \(user[email])")
        }
    }
}

我第一次运行的时候，输出是：

("SELECT * FROM \"users\"", [])
id: 1, email: alice@mac.com

然后我删除第 17 行（try! db.run(users.insert(email <- "alice@mac.com"))）并再次运行，调试器输出更改为：

("SELECT * FROM \"users\"", [])

看起来alice@mac.com 没有保存到数据库。那我哪里做错了？或者如何保存到 SQLite 数据库中？

附：我正在使用 Xcode 7 beta 5、Swift 2.0

Answer 1

viewDidLoad 首先创建表，然后插入。

当表已经存在时，我不知道表创建函数的行为，但如果它没有对您抛出任何错误，它可能会再次重新创建表。如果是这种情况，在调用 viewDidLoad 并注释掉插入后，您可能最终会得到一个全新的空白表。

尝试更改逻辑以确保不会每次都重新创建表。

Answer 2

let db = try! Connection()

创建一个 in-memory 数据库，您可以从 API 文档中看到：

/// Initializes a new SQLite connection.
///
/// - Parameters:
///
///   - location: The location of the database. Creates a new database if it
///     doesn’t already exist (unless in read-only mode).
///
///     Default: `.InMemory`.
///
///   - readonly: Whether or not to open the database in a read-only state.
///
///     Default: `false`.
///
/// - Returns: A new database connection.
public init(_ location: Location = .InMemory, readonly: Bool = false) throws

数据不会持久化到文件中，数据库始终是初始状态 空。

对于持久数据库，使用

/// Initializes a new connection to a database.
///
/// - Parameters:
///
///   - filename: The location of the database. Creates a new database if
///     it doesn’t already exist (unless in read-only mode).
///
///   - readonly: Whether or not to open the database in a read-only state.
///
///     Default: `false`.
///
/// - Throws: `Result.Error` iff a connection cannot be established.
///
/// - Returns: A new database connection.
public convenience init(_ filename: String, readonly: Bool = false) throws

例如

// Compute file path for database in Documents directory:
let docsDir = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true).last!
let dbPath = (docsDir as NSString).stringByAppendingPathComponent("database.sqlite")

do {
    let db = try Connection(dbPath)
    // ... use database

} catch (error) {
    // Could not create or open database, print error
}

Answer 3

你可以有这样的东西（显然其他人都可以改进代码）：

1. 创建表格模型：

   class TUsers {
   static let TABLE_NAME : String = “users”
   static let ID = Expression<Int64>("id")
   static let EMAIL = Expression<String>(“email”)
   static let NAME = Expression<String>(“name”)
   
   class func addUser(email : String!, name : String!) -> Bool{
   
       let users = Table(TABLE_NAME)
   
       do {
   
           try DBHelper.instance.db.run(users.insert(
               TUsers.EMAIL <- email,
               TUsers.NAME <- name
           ))
   
           return true
       } catch {
           print("Insert failed")
           return false
       }
   }
   
   class func getAllUsers() -> [User] { // you must create the model user
       let users = Table(TUsers.TABLE_NAME)
   
       let query = users.select(*)
           //.filter(TUsers.EMAIL == “whatever@pomberobota.com”)
   
       var listOfUsers : [Users] = []
   
       for user in DBHelper.instance.db.prepare(query) {
           // Do whatever you need to instantiate the model User
   
   
           listOfUsers.append(User(email: users[TUsers.EMAIL], name: users[TUsers.NAME])
   
       }
   
       return listOfUsers
   }
   }
   

2. 创建一个数据库助手

   class DBHelper {
   
   static let instance = DBHelper()
   
   var db : Connection
   
   init() {
       do {
           self.db = try Connection("\(Util.getDBPath())/db.sqlite3")
           createTablesIfNotExists()
       } catch {
           print("Could not create a connection to database")
       }
   }
   
   func createTablesIfNotExists() {
   
       let users = Table(TUsers.TABLE_NAME)
       do {
           try db.run(logs.create(ifNotExists: true) { t in
                   t.column(TUsers.ID, primaryKey: true)
                   t.column(TUsers.EMAIL)
                   t.column(TUsers.NAME)
           })
       } catch {
           print(“Could not create table users”)
       }
   }
   }
   

3. 最后（这里你不需要导入 SQLite）。

   class ViewController: UIViewController {
   override func viewDidLoad() {
       super.viewDidLoad()
   
      TUsers.addUser(“user@ndetavysho.com”, “John Capuchon”)
   
       let users = TUsers.getAllUsers()
   
       for user in users {
           // do something
       }
   }
   

   }