IOS開發-數據庫總結

時間 2019-11-18

標籤 ios 開發數據庫總結欄目 iOS 简体版

原文原文鏈接

關於數據存儲概念：html

數據結構：ios

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

存儲方式：git

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做的過程。github

經常使用的數據存儲方案：sql

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 也屬於屬性列表存儲，經常使用數據庫

　　　　　　　　於存儲配置信息。這個機制能夠將這些對象直接序列化到 plist 文件中，多用數組

　　　　　　　　於少許數據的存儲，效率較高。緩存

simple code:數據結構

    // 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];  
    //操做完若修改了數據則，寫入文件  
    [array writeToFile:myFile atomically:YES];

對象歸檔: 自定義對象經常使用的存儲機制，對象必須實現 NSCoding 協議，NSCopying協議可選

simple code架構

 #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，我的偏向於使用基於運行時的一個方案：

須要歸檔的對象只須要繼承便可。

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

SQLite: 用於存儲查詢需求較多的數據

iOS的SDK裏預置了SQLite3的庫，開發者能夠自建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差很少，也是基礎類型的小數據，只是從組織形式上不一樣。開發者能夠以關係型

數據庫的方式組織數據，使用SQL DML來管理數據。通常來講應用中的格式化的文本類

數據能夠存放在數據庫中，尤爲是相似聊天記錄、Timeline等這些具備條件查詢和排序需

求的數據。每個數據庫的句柄都會在內存中都會被分配一段緩存，用於提升查詢效率。

另外一個方面，因爲查詢緩存，當產生大量句柄或數據量較大時，會出現緩存過大，形成

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);
    }
}