IOS開發-數據庫總結

2019-11-14 20:01:35

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來源：轉載

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關于數據存儲概念：

數據結構：

基本對象：NSDictionary、NSArray和NSSet這些對象。
復雜對象：關系模型、對象圖和屬性列表多種結構等。

存儲方式：

內存：內存存儲是臨時的，運行時有效的，但效率高。
閃存：閃存則是一種持久化存儲，但產生I/O消耗，效率相對低。

歸檔：把內存數據轉移到閃存中進行持久化的操作的過程。

常用的數據存儲方案：

屬性列表：NSArray、NSDictionary、NSData、NSString、NSNumber、NSDate等

　　　　　　　　基本數據類型都支持這個機制，NSUserDefaults 也屬于屬性列表存儲，常用

　　　　　　　　于存儲配置信息。這個機制可以將這些對象直接序列化到 plist 文件中，多用

　　　　　　　　于少量數據的存儲，效率較高。

simple code:

    // NSUserDefaults 默認    NSUserDefaults *userDefaults =  [NSUserDefaults standardUserDefaults];    [userDefaults setObject:@"skyming" forKey:@"username"];    [userDefaults setObject:[NSDate date] forKey:@"date"];    [userDefaults setObject:@[@"a1",@"a2"] forKey:@"array"];    [userDefaults setInteger:6174 forKey:@"code"];    NSLog(@"userDefaults: %@",[userDefaults dictionaryRePResentation]);        NSString *username = [userDefaults objectForKey:@"username"];    NSDate *date = [userDefaults objectForKey:@"date"];    NSArray *array = [userDefaults objectForKey:@"array"];    NSInteger code = [userDefaults integerForKey:@"code"];        NSLog(@"username: %@  date:%@  /n array: %@ code: %d", username, date, array, code);    [userDefaults synchronize];    // NSUserDefaults 自定義    NSUserDefaults *defaults = [[NSUserDefaults alloc] init];    [defaults setPersistentDomain:[NSDictionary dictionaryWithObject:@"Hello" forKey:@"World"] forName:@"com.Sensoro.DefaultsTest"];    [defaults synchronize];//  數組    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);      NSString *docPath = [paths objectAtIndex:0];      NSString *myFile = [docPath stringByAppendingPathComponent:@"my.list"];      //讀取文件      NSArray *array = [[NSArray alloc] initWithContentsOfFile:myFile];      //操作完若修改了數據則，寫入文件      [array writeToFile:myFile atomically:YES];

對象歸檔: 自定義對象常用的存儲機制，對象必須實現 NSCoding 協議，NSCopying協議可選

simple code

 #pragma mark -#pragma NSCoding協議實現實現- (void)encodeWithCoder:(NSCoder *)aCoder{   //encoder    [aCoder encodeObject:self.username forKey:@"username"];    [aCoder encodeObject:self.passWord forKey:@"password"];}- (id)initWithCoder:(NSCoder *)aDecoder{    //decoder    if (self = [super init]) {        self.username = [aDecoder decodeObjectForKey:@"username"];        self.password =  [aDecoder decodeObjectForKey:@"password"];    }    return self;}#pragma NSCopying協議實現- (id)copyWithZone:(NSZone *)zone{    DSObj *copy = [[[self class] allocWithZone:zone] init];    return copy;}// 讀取        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);    NSString *docPath = [paths objectAtIndex:0];    NSString *myFile = [docPath stringByAppendingPathComponent:@"dsObj.list"];        //寫入歸檔文件    NSMutableData *datawrite = [[NSMutableData alloc] init];    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:datawrite];    [archiver encodeObject:test forKey:@"data"];    [archiver finishEncoding];    [datawrite writeToFile:myFile atomically:YES];        //讀取歸檔文件    NSData *data = [[NSMutableData alloc] initWithContentsOfFile:myFile];    NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];    DSObj *testread = [unarchiver decodeObjectForKey:@"data"];    [unarchiver finishDecoding];    NSLog(@"DSObjRead: %@ %@",[testread username], [testread password]);

當屬性多時總不能一個個的添加吧，個人偏向于使用基于運行時的一個方案：

需要歸檔的對象只需要繼承即可。

鏈接： https://github.com/skyming/SSObjectBase

SQLite: 用于存儲查詢需求較多的數據

iOS的SDK里預置了SQLite3的庫，開發者可以自建SQLite數據庫。SQLite每次寫入數據

都會產生IO消耗，把數據歸檔到相應的文件。SQLite擅長處理的數據類型其實與NSUser-

Defaults差不多，也是基礎類型的小數據，只是從組織形式上不同。開發者可以以關系型

數據庫的方式組織數據，使用SQL DML來管理數據。一般來說應用中的格式化的文本類

數據可以存放在數據庫中，尤其是類似聊天記錄、Timeline等這些具有條件查詢和排序需

求的數據。每一個數據庫的句柄都會在內存中都會被分配一段緩存，用于提高查詢效率。

另一個方面，由于查詢緩存，當產生大量句柄或數據量較大時，會出現緩存過大，造成

內存浪費。

simple code

//open database- (void)openDataBase{    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);    NSString *docPath = [paths objectAtIndex:0];    NSString *myFile = [docPath stringByAppendingPathComponent:@"data.db"];        if (sqlite3_open([myFile UTF8String], &database)==SQLITE_OK)    {        NSLog(@"open sqlite db ok.");    }    else    {        NSLog( @"can not open sqlite db " );                //close database        sqlite3_close(database);    }}//create table- (void)createTable{    char *errorMsg;    const char *createSql="create table if not exists persons (id integer primary key autoincrement,name text)";        if (sqlite3_exec(database, createSql, NULL, NULL, &errorMsg)==SQLITE_OK)    {        NSLog(@"create ok.");    }    else    {        NSLog( @"can not create table" );        [self ErrorReport:[NSString stringWithFormat:@"%s",createSql]];    }}//insert table- (void)insertTable{    char *errorMsg;        const char *insertSql="insert into persons (name) values ('skyming')";    if (sqlite3_exec(database, insertSql, NULL, NULL, &errorMsg)==SQLITE_OK)    {        NSLog(@"insert ok.");    }    else    {        NSLog( @"can not insert it to table" );        [self ErrorReport:[NSString stringWithFormat:@"%s",insertSql]];    }}//query table- (void)queryTable{    const char *selectSql="select id,name from persons";    sqlite3_stmt *statement;    if (sqlite3_prepare_v2(database, selectSql, -1, &statement, nil)==SQLITE_OK)    {        NSLog(@"select ok.");        while (sqlite3_step(statement)==SQLITE_ROW)//SQLITE_OK SQLITE_ROW        {            int _id=sqlite3_column_int(statement, 0);            NSString *name=[[NSString alloc] initWithCString:(char *)sqlite3_column_text(statement, 1) encoding:NSUTF8StringEncoding];            NSLog(@"row>>id %i, name>> %@",_id,name);        }            }    else    {        //error        [self ErrorReport:[NSString stringWithFormat:@"%s",selectSql]];    }        sqlite3_finalize(statement);}//delete table- (void)deleteTable{    char *errorMsg;    [self openDataBase];        const char *sql = "DELETE FROM persons where id=24";    if (sqlite3_exec(database, sql, NULL, NULL, &errorMsg)==SQLITE_OK)    {        NSLog(@"delete ok.");    }    else    {        NSLog( @"can not delete it" );        [self ErrorReport:[NSString stringWithFormat:@"%s",sql]];    }    }//error- (void)ErrorReport: (NSString *)item{    char *errorMsg;        if (sqlite3_exec(database, [item cStringUsingEncoding:NSUTF8StringEncoding], NULL, NULL, &errorMsg)==SQLITE_OK)    {        NSLog(@"%@ ok.",item);    }    else    {        NSLog(@"error: %s",errorMsg);        sqlite3_free(errorMsg);    }}