SQLite简介

SQLite，是一款轻型的数据库，是遵守ACID的关系型数据库管理系统，它包含在一个相对小的C库中。它是D.RichardHipp建立的公有领域项目。它的设计目标是嵌入式的，而且目前已经在很多嵌入式产品中使用了它，它占用资源非常的低，在嵌入式设备中，可能只需要几百K的内存就够了。它能够支持Windows/Linux/Unix等等主流的操作系统，同时能够跟很多程序语言相结合，比如 Tcl、C#、PHP、Java等，还有ODBC接口，同样比起Mysql、PostgreSQL这两款开源的世界著名数据库管理系统来讲，它的处理速度比他们都快。

SQLite支持的存储类型

1、INTEGER - 整形

2、blob - 二进制

3、real - 浮点型

4、text - 字符串

5、NULL - 空

SQLite优势

1、占用资源低

2、速度快

3、与其他数据库相比，更适配移动平台、嵌入式平台

SQLite基本使用

//定义数据库变量
    var db:OpaquePointer? = nil
    
    //打开数据库
    func openDB() ->Bool{
        
        if db != nil {
            print("数据库已经打开")
            return true
        }
        
        //数据库文件路径
        let dicumentPath = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true).last
//        let dbPath =  (dicumentPath as NSString).appendingPathComponent("test.sqlite")
        let dbPath = (dicumentPath! as NSString).appendingPathComponent("appDB.sqlite")
        
        let cDBPath = dbPath.cString(using: String.Encoding.utf8)
        print(dbPath)
        //打开数据库
        //第一个参数:数据库文件路径  第二个参数:数据库对象
        if sqlite3_open(cDBPath, &db) != SQLITE_OK{
            print("打开失败")
        }
        print("openDB")
        return createTable()
    }
     //创建表
    func createTable() -> Bool{
        //建表的SQL语句  
        let creatUserTable = "CREATE TABLE IF NOT EXISTS t_cache ( equipmentID TEXT NOT NULL PRIMARY KEY,sswitch1 TEXT,sswitch2 TEXT,svolume TEXT,mp3 TEXT);"
        
//         let creatCarTable = "CREATE TABLE IF NOT EXISTS 't_Car' ('ID' INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,'type' TEXT,'output' REAL,'master' TEXT);"
        //执行SQL语句-创建表 依然,项目中一般不会只有一个表
        print("createTable")
        return creatTableExecSQL(SQL_ARR: [creatUserTable])
        
    }
    //执行建表SQL语句
    func creatTableExecSQL(SQL_ARR : [String]) -> Bool {
        for item in SQL_ARR {
            if execSQL(SQL: item) == false  {
                return false
            }
        }
        print("creatTableExecSQL")
        return true
    }
    
    //执行SQL语句
    func execSQL(SQL : String) -> Bool{
        // 1.将sql语句转成c语言字符串
        let cSQL = SQL.cString(using: String.Encoding.utf8)
         //错误信息
        let errmsg : UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>? = nil
        if sqlite3_exec(db, cSQL, nil, nil, errmsg) == SQLITE_OK {
            print("execSQL")
            return true
        }else{
            print("SQL 语句执行出错 -> 错误信息: 一般是SQL语句写错了 \(errmsg)")
        return false
        }
    }

    关闭数据库
    func closeDB()-> Void{
    let result = sqlite3_close(db)
        if result == SQLITE_OK {
            db = nil
            print("数据库关闭")
        }else{
        print("关闭失败")
        }
    }

插入数据
func insertData(_ user : CacheSeting) -> Bool{
        _ = openDB()
        var stmt : OpaquePointer? = nil
        let sql = "INSERT INTO t_cache(equipmentID,sswitch1,sswitch2,svolume,mp3) VALUES ('\(user.equipmentID)','\(user.sswitch1)','\(user.sswitch2)','\(user.svolume)','\(user.mp3)')"
        let cSql = sql.cString(using: .utf8)
        let prepare_result = sqlite3_prepare_v2(db, cSql, -1, &stmt, nil)
        if prepare_result != SQLITE_OK {
            sqlite3_finalize(stmt)
            if (sqlite3_errmsg(db)) != nil {
                let msg = "SQLiteDB - failed to prepare SQL:\(sql)"
                print(msg)
            }
            return false
        }
        print(sql)
        sqlite3_bind_text(stmt, 1, user.equipmentID.cString(using: .utf8), -1, nil)
        sqlite3_bind_text(stmt, 2, user.sswitch1.cString(using: .utf8), -1, nil)
        sqlite3_bind_text(stmt, 3, user.sswitch2.cString(using: .utf8), -1, nil)
        sqlite3_bind_text(stmt, 4, user.svolume.cString(using: .utf8), -1, nil)
        sqlite3_bind_text(stmt, 5, user.mp3.cString(using: .utf8), -1, nil)
//        sqlite3_bind_text(stmt, 6, user.disturb.cString(using: .utf8), -1, nil)
        
        let step_result = sqlite3_step(stmt)
        
        if step_result != SQLITE_OK && step_result != SQLITE_DONE {
            sqlite3_finalize(stmt)
            if (sqlite3_errmsg(db)) != nil {
                let msg = "SQLiteDB - failed to execute SQL:\(sql)"
                print(msg)
            }
            return false
        }
        sqlite3_finalize(stmt)
        
        return true
    }

查询
 func selectToUserName(userID : String)-> CacheSeting{
        _ = openDB()
        let sql = "SELECT * FROM t_cache where equipmentID = '\(userID)'"
        let user = CacheSeting()
        var stmt:OpaquePointer? = nil
        let cSql = sql.cString(using: .utf8)
        
        let prepare_result = sqlite3_prepare_v2(db, cSql!, -1, &stmt, nil)
        if prepare_result != SQLITE_OK{
            sqlite3_finalize(stmt)
            if (sqlite3_errmsg(db)) != nil {
                let msg = "SQLiteDB - failed to prepare SQL:\(sql)"
                print(msg)
            }
        }
        
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            let myid = UnsafePointer(sqlite3_column_text(stmt, 0))
            let switch1 = UnsafePointer(sqlite3_column_text(stmt, 1))
            let switch2 = UnsafePointer(sqlite3_column_text(stmt, 2))
            let myvloum = UnsafePointer(sqlite3_column_text(stmt, 3))
            let myMP3 = UnsafePointer(sqlite3_column_text(stmt, 4))
//            let myDisturb = UnsafePointer(sqlite3_column_text(stmt, 5))
            user.equipmentID = String.init(cString: myid!)
            user.sswitch1 = String.init(cString: switch1!)
            user.sswitch2 = String.init(cString: switch2!)
            user.svolume = String.init(cString: myvloum!)
            user.mp3 = String.init(cString: myMP3!)
//            user.disturb = String.init(cString: myDisturb!)
            
        }
        sqlite3_finalize(stmt)
        return user
    }

更新数据
func updataMP3(userID:String , toMP3:String)->Bool{
        _ = openDB()
        let sql = "update t_cache set mp3 = '\(toMP3)'where equipmentID = '\(userID)'";
        //定义伴随指针
        var stmt:OpaquePointer? = nil
        //sql语句转换成cString类型
        let cSql = sql.cString(using: .utf8)
        //编译sql
        let prepare_result = sqlite3_prepare_v2(db, cSql!, -1, &stmt, nil)
        //判断如果失败，获取失败信息
        if prepare_result != SQLITE_OK{
            sqlite3_finalize(stmt)
            if (sqlite3_errmsg(db)) != nil {
                let msg = "SQLiteDB - failed to prepare SQL:\(sql)"
                print(msg)
            }
        }
        //step执行
        let step_result = sqlite3_step(stmt)
        //判断执行结果，如果失败，获取失败信息
        if step_result != SQLITE_OK && step_result != SQLITE_DONE {
            sqlite3_finalize(stmt)
            if (sqlite3_errmsg(db)) != nil {
                let msg = "SQLiteDB - failed to execute SQL:\(sql)"
                print(msg)
            }
            return false
        }
        //释放跟随指针
        sqlite3_finalize(stmt)
        
        return true
    }

删除数据
func deleteToUserId(userID : Int)-> Bool{
        //删除sql语句
        let sql = "delete from t_User where id = '\(userID)'"
        //定义伴随指针
        var stmt:OpaquePointer? = nil
        //sql语句转换成cString类型
        let cSql = sql.cString(using: .utf8)
        //编译sql
        let prepare_result = sqlite3_prepare_v2(db, cSql!, -1, &stmt, nil)
        //判断如果失败，获取失败信息
        if prepare_result != SQLITE_OK{
            sqlite3_finalize(stmt)
            if (sqlite3_errmsg(db)) != nil {
                let msg = "SQLiteDB - failed to prepare SQL:\(sql)"
                print(msg)
            }
        }
        //step执行
        let step_result = sqlite3_step(stmt)
        //判断执行结果，如果失败，获取失败信息
        if step_result != SQLITE_OK && step_result != SQLITE_DONE {
            sqlite3_finalize(stmt)
            if (sqlite3_errmsg(db)) != nil {
                let msg = "SQLiteDB - failed to execute SQL:\(sql)"
                print(msg)
            }
            return false
        }
        //释放跟随指针
        sqlite3_finalize(stmt)
        
        return true
    }

以上就是数据库的简单操作了，SQLite里面还有很多的操作需要值得注意，比如说在多线程中执行的时候是有安全隐患的，可能会发生这里在执行插入、另外又在执行删除、更新或者其他的指令，所以多线程操作数据库一定要保证线程安全，这方面我还没着手去写，等有试过了再更新。