iOS编程，数据库

代码�：

首先导入头文件(#import )

#pragma mark ** 单例
+ (instancetype)shareDataBaseHandler {
    
    // 在静态区, 只初始化一次.
    static DataBaseHandler *dataBase = nil;
    
    if (dataBase == nil) {
        
        dataBase = [[DataBaseHandler alloc] init];
        
    }
    
    return dataBase;
}


#pragma mark ** 定义一个sqlite 结构体(对象)
sqlite3 *db;


#pragma mark ** 打开数据库
- (void)openDataBase {
    
    // API: sqlite3_open.
    if (db != nil) {
        
        NSLog(@"数据库已经开启!!!");
        
        return;
    }
    
    // 文件路径.
    NSString *file = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"collect.sqlite"];
    
    int result = sqlite3_open(file.UTF8String, &db);
    
    if (result == SQLITE_OK) {
        
//        NSLog(@"数据库打开成功!");
        
    } else {
        
        NSLog(@"数据库打开失败, code = %d", result);
    }
    
}


#pragma mark ** 创建表格
- (void)createTable {
    
    // API: sqlite3_exec.
    
    // 创建SQL 语句.
    NSString *createTableSQL = @"CREATE TABLE IF NOT EXISTS model(number integer PRIMARY KEY AUTOINCREMENT, name text, photo text, id text)";
    
    int result = sqlite3_exec(db, createTableSQL.UTF8String, NULL, NULL, nil);
    
    if (result == SQLITE_OK) {
        
//        NSLog(@"创建表格成功");
        
    } else {
        
        NSLog(@"表格创建失败, code = %d", result);
        
    }
    
}


#pragma mark ** 插入数据
- (void)insertModel:(ModelForTravels *)model {
    
    // API: sqlite3_exec.
    NSString *insertSQL = [NSString stringWithFormat:@"INSERT into model(name, photo, id) VALUES('%@', '%@', '%@')", model.name, model.front_cover_photo_url, model.id_count];
    
    int result = sqlite3_exec(db, insertSQL.UTF8String, nil, nil, nil);
    
    if (result == SQLITE_OK) {
        
    } else {
        
    }
    
}


#pragma mark ** 删除数据
- (void)deleteWithName:(NSString *)name {
    
    // API: sqlite3_exec.
    NSString *deleteSQL = [NSString stringWithFormat:@"DELETE FROM model WHERE name = '%@'", name];
    
    int result = sqlite3_exec(db, deleteSQL.UTF8String, nil, nil, nil);
    
    if (result == SQLITE_OK) {
        
    } else {
        
    }
    
}


#pragma mark ** 查询数据
- (NSMutableArray *)selectAllData {
    
    // 存放符合条件的数据(元素是Model 对象).
    NSMutableArray *array = [NSMutableArray array];
    
    // sql 语句.
    NSString *selectSQL = [NSString stringWithFormat:@"SELECT * FROM model"];
    
    // API: stmt 结构体, sqlite3_prepareV2, sqlite3_step, sqlite3_column.
    
    // 声明一个stmt 对象(结构体).
    sqlite3_stmt *stmt = nil;
    
    int result = sqlite3_prepare_v2(db, selectSQL.UTF8String, -1, &stmt, nil);
    
    if (result == SQLITE_OK) {
        
        // 每行都执行查询语句.
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            
            // 如果查询条件匹配, 通过sqlite3_column (函数簇), 取出值.
            
            // 取出哪一列的数据.
            const unsigned char *name = sqlite3_column_text(stmt, 1);
            
            const unsigned char *photo = sqlite3_column_text(stmt, 2);
            
            const unsigned char *id_count = sqlite3_column_text(stmt, 3);
            
            // 创建Model 对象, 赋值之后放到数组中.
            ModelForTravels *model = [[ModelForTravels alloc] init];
            
            model.name = [NSString stringWithUTF8String:(const char *) name];
            
            model.front_cover_photo_url = [NSString stringWithUTF8String:(const char *) photo];
            
            model.id_count = [NSString stringWithUTF8String:(const char *) id_count];
            
            [array insertObject:model atIndex:0];
            
        }
        
        // 销毁对象.
        sqlite3_finalize(stmt);
        
    } else {
        
        // 销毁对象.
        sqlite3_finalize(stmt);
        
    }
    
    return array;
}


#pragma mark ** 删除表格
- (void)dropTable {
    
    NSString *dropSQL = @"DROP TABLE model";
    
    int result = sqlite3_exec(db, dropSQL.UTF8String, nil, nil, nil);
    
    if (result == SQLITE_OK) {
        
    } else {
        
    }
    
}


#pragma mark ** 关闭数据库
- (void)closeDB {
    
    // API: sqlite3_close.
    int result = sqlite3_close(db);
    
    if (result == SQLITE_OK) {
        
        db = nil;
        
    } else {
        
    }
    
}