@TOC

IOS數(shù)據(jù)存儲簡介

• 在項目開發(fā)當(dāng)中，我們經(jīng)常會對一些數(shù)據(jù)進行本地緩存處理岛都。離線緩存的數(shù)據(jù)一般都保存在APP所在的沙盒之中淑履。一般有以下幾種：

IOS 沙盒存儲路徑

• 要存儲數(shù)據(jù)担败，必須要了解蘋果的沙盒存儲機制，沙盒相關(guān)路徑的規(guī)則

• 獲取沙盒路徑

// 獲取Documents目錄的路徑
NSString *documentPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).lastObject;
// 得到Document目錄下的fileName文件的路徑
NSString *filePath = [documentPath stringByAppendingPathComponent:fileName];

//獲取Library/Caches目錄路徑
NSString *path = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).firstObject;
//獲取Library/Caches目錄下的fileName文件路徑
NSString *filePath = [path stringByAppendingPathComponent:fileName];

//獲取temp路徑
NSString *tmp = NSTemporaryDirectory();
//獲取temp下fileName文件的路徑
NSString *filePath = [tmp stringByAppendingPathComponent:fileName];

IOS數(shù)據(jù)存儲方式

1. PList(XML屬性列表)

• 在使用plist進行數(shù)據(jù)存儲和讀取肥照，只適用于系統(tǒng)自帶的一些常用類型才能用脚仔，且必須先獲取路徑相對麻煩
• 可以把字典或數(shù)組直接寫入到文件中。另外舆绎，NSString玻侥、NSData、NSNumber等類型亿蒸，也可以使用writeToFile:atomically:方法直接將對象寫入文件中凑兰，只是Type為空。
• 實例1

oc代碼

//寫入文件
NSString *doc = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSString *path = [doc stringByAppendingPathComponent:@"myself.plist"];
NSDictionary *dict = @{@"name": @"yixiang"};
[dict writeToFile:path atomically:YES];
//讀取文件
NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:path];

2. 偏好設(shè)置（NSUserDefaults）

• 將所有的東西都保存在同一個文件夾下面边锁，且主要用于存儲應(yīng)用的設(shè)置信息）
• NSUserDefaults可以存儲的數(shù)據(jù)類型包括：NSData姑食、NSString、NSNumber茅坛、NSDate音半、NSArray则拷、NSDictionary。如果要存儲其他類型曹鸠，則需要轉(zhuǎn)換為前面的類型煌茬，才能用NSUserDefaults存儲。
• 實例2
  OC代碼

//寫入文件
NSUserDefaults *defaults=[NSUserDefaults standardUserDefaults];
[defaults setObject:@"yixiang" forKey:@"name"];
[defaults setInteger:27 forKey:@"age"];
[defaults synchronize];
//讀取文件
NSUserDefaults *defaults=[NSUserDefaults standardUserDefaults];
NSString *name=[defaults objectForKey:@"name"];
NSInteger age=[defaults integerForKey:@"age"];

3. 歸檔（NSCoding NSKeyedArchiver NSKeyedUnarchiver）

• 因為PList存儲和NSUserDefaults存儲都有一個致命的缺陷彻桃，只能存儲常用的類型坛善。歸檔可以實現(xiàn)把自定義的對象存放在文件中。
• 需要保存的對象必須遵守NSCoding協(xié)議邻眷，并且實現(xiàn)該協(xié)議中- (void)encodeWithCoder:(NSCoder )aCoder和 - (id)initWithCoder:(NSCoder )aDecoder方法眠屎。
• 實例3
  OC代碼

//YXPerson.h文件如下：

@interface YXPerson : NSObject<NSCoding>
  @property(nonatomic,copy) NSString *name;
  @property(nonatomic,assign) int age;
  @end
//YXPerson.m文件如下：

 #import "YYPerson.h"

  @implementation YYPerson
  -(void)encodeWithCoder:(NSCoder *)aCoder{
      [aCoder encodeObject:self.name forKey:@"name"];
      [aCoder encodeInteger:self.age forKey:@"age"];
  }
  -(id)initWithCoder:(NSCoder *)aDecoder{
      if (self=[super init]) {
          self.name=[aDecoder decodeObjectForKey:@"name"];
          self.age=[aDecoder decodeIntegerForKey:@"age"];
      }
      return self;
  }
  @end

在ViewController中對它進行寫入和讀取

 //寫入對象
    YXPerson *p=[[YXPerson alloc]init];
    p.name=@"yixiang";
    p.age=27;

    NSString *docPath=[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)lastObject];
    NSString *path=[docPath stringByAppendingPathComponent:@"person.yixiang"];

    [NSKeyedArchiver archiveRootObject:p toFile:path];

     //讀取對象
     YXPerson *p=[NSKeyedUnarchiver unarchiveObjectWithFile:path];

4. SQLITE數(shù)據(jù)庫

• 上述三種方法都無法存儲大批量的數(shù)據(jù)，有性能的問題肆饶。

• SQLITE作為程序員都比較熟悉改衩，它是跨平臺的數(shù)據(jù)庫工具。下面簡單介紹一下驯镊，如何打開數(shù)據(jù)庫葫督，新增一張表格，然后對其進行增刪改查的操作板惑。

• 詳細(xì)SQLite相關(guān)性能優(yōu)化可以參考這篇文章：微信iOS SQLite源碼優(yōu)化實踐

• 實例4
  OC代碼

- (void)openDB{
    //獲取數(shù)據(jù)庫文件路徑
    NSString *doc = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *fileName = [doc stringByAppendingPathComponent:@"students.sqlite"];

    //將OC字符串轉(zhuǎn)換為c語言的字符串
    const char *cfileName = fileName.UTF8String;

    //打開數(shù)據(jù)庫文件（如果數(shù)據(jù)庫文件不存在候衍，那么該函數(shù)會自動創(chuàng)建數(shù)據(jù)庫文件）
    int result = sqlite3_open(cfileName, &_db);
    if (result == SQLITE_OK) {//打開成功
        NSLog(@"成功打開數(shù)據(jù)庫");
    }else{
        NSLog(@"打開數(shù)據(jù)庫失敗");
    }
}


- (void)createTable{
    //創(chuàng)建表
    const char *sql = "CREATE TABLE IF NOT EXISTS t_student(id integer PRIMARY KEY AUTOINCREMENT,name text NOT NULL,age integer NOT NULL);";
    char *errmsg= NULL;
    int result = sqlite3_exec(_db, sql, NULL, NULL, &errmsg);
    if (result==SQLITE_OK) {
        NSLog(@"創(chuàng)建表成功");
    }else{
        NSLog(@"創(chuàng)建表失敗---%s",errmsg);
    }
}


- (void)insertData{
    //插入數(shù)據(jù)
    for (int i=0; i<10; i++) {
        //拼接sql語句
        NSString *name = [NSString stringWithFormat:@"yixiangboy--%d",arc4random_uniform(100)];
        int age = arc4random_uniform(20)+10;
        NSString *sql = [NSString stringWithFormat:@"INSERT INTO t_student (name,age) VALUES ('%@',%d);",name,age];

         //執(zhí)行SQL語句
        char *errmsg = NULL;
        sqlite3_exec(_db, sql.UTF8String, NULL, NULL, &errmsg);
        if (errmsg) {//如果有錯誤信息
            NSLog(@"插入數(shù)據(jù)失敗--%s",errmsg);
        }else{
            NSLog(@"插入數(shù)據(jù)成功");
        }
    }
}


- (void)deleteData{
    //刪除age小于15的數(shù)據(jù)
    NSString *sql = [NSString stringWithFormat:@"DELETE FROM t_student WHERE age<15"];
    char *errmsg = NULL;
    sqlite3_exec(_db, sql.UTF8String, NULL, NULL, &errmsg);
    if (errmsg) {
        NSLog(@"刪除數(shù)據(jù)失敗");
    }else{
        NSLog(@"刪除數(shù)據(jù)成功");
    }
}

- (void)updateData{
    //大于20歲的都置為20歲
    NSString *sql = [NSString stringWithFormat:@"UPDATE t_student set age=20 WHERE age>20"];
    char *errmsg = NULL;
    sqlite3_exec(_db, sql.UTF8String, NULL, NULL, &errmsg);
    if (errmsg) {
        NSLog(@"更新數(shù)據(jù)失敗");
    }else{
        NSLog(@"更新數(shù)據(jù)成功");
    }
}


- (void)queryData{
    const char *sql = "SELECT id,name,age FROM t_student WHERE age<20";
    sqlite3_stmt *stmt = NULL;

    //進行查詢前的準(zhǔn)備工作
    if(sqlite3_prepare_v2(_db, sql, -1, &stmt, NULL)==SQLITE_OK){//SQL語句沒有問題
        NSLog(@"查詢語句沒有問題");

        //每調(diào)用一次sqlite3_step函數(shù)，stmt就會指向下一條記錄
        while (sqlite3_step(stmt)==SQLITE_ROW) {//找到一條記錄
            //取出數(shù)據(jù)
            //(1)取出第0個字段的值（int）
            int ID=sqlite3_column_int(stmt, 0);
            //(2)取出第一列字段的值(text)
            const unsigned char *name = sqlite3_column_text(stmt, 1);
            //(3)取出第二列字段的值(int)
            int age = sqlite3_column_int(stmt, 2);

            printf("%d %s %d\n",ID,name,age);
        }
    }else{
        NSLog(@"查詢語句有問題");
    }
}

5. FMDB

5.1 FMDB 簡介

• FMDB 做IOS的也應(yīng)該都耳熟能詳了洒放，項目中都用過。是一個很牛逼的DB工具滨砍。
• FMDB 是對SQLIite數(shù)據(jù)庫的C語言接口進行了一層封裝往湿，使其滿足面向?qū)ο蟮牟僮鳎涌诒仍腟QLite接口簡潔很多惋戏。同時也提供一些多線程领追，緩存，線程池的功能响逢。
• FMDB的三個類：

5.2 FMDB 創(chuàng)建數(shù)據(jù)庫

• FMDatabase創(chuàng)建的時候需要提供一個SQLite數(shù)據(jù)庫文件些膨。我們一般提供一個.db的文件路徑即可。

NSString *path = [NSTemporaryDirectory() stringByAppendingPathComponent:@"tmp.db"];
FMDatabase *db = [FMDatabase databaseWithPath:path];

5.3 FMDB 打開數(shù)據(jù)庫钦铺，關(guān)閉數(shù)據(jù)庫

• 打開數(shù)據(jù)庫：在和數(shù)據(jù)庫進行交互之前订雾，我們需要先打開數(shù)據(jù)庫。使用上一步拿到的數(shù)據(jù)庫文件操作句柄db

if (![db open]) 
{
    db = nil;
    return;
}

• 關(guān)閉數(shù)據(jù)庫

[db close];

5.4 FMDB 創(chuàng)建表

• 使用集合語句來進行表的創(chuàng)建矛洞。

NSString *sql = @"create table bulktest1 (id integer primary key autoincrement, x text);"
                 "create table bulktest2 (id integer primary key autoincrement, y text);"
                 "create table bulktest3 (id integer primary key autoincrement, z text);"
                 "insert into bulktest1 (x) values ('XXX');"
                 "insert into bulktest2 (y) values ('YYY');"
                 "insert into bulktest3 (z) values ('ZZZ');";

success = [db executeStatements:sql];

5.5 FMDB 增洼哎，刪，改，查

5.5.1 查詢

• 查詢：使用executeQuery 來執(zhí)行查詢語句噩峦，F(xiàn)MResultSet來進行存儲查詢的結(jié)果锭沟。

FMResultSet *s = [db executeQuery:@"SELECT * FROM myTable"];
while ([s next]) {
    //retrieve values for each record
}

//可通過如下的方式將結(jié)果集里面的數(shù)據(jù)取出來。

while ([rs next])
{
    if (oldIDs == nil) oldIDs = [[NSMutableArray alloc] init];
    [oldIDs addObject:[rs stringForColumnIndex:0]];
}

另外识补，F(xiàn)MResultSet可以通過如下的方法將數(shù)據(jù)通過恰當(dāng)?shù)母袷綑z索出來族淮。

intForColumn:
longForColumn:
longLongIntForColumn:
boolForColumn:
doubleForColumn:
stringForColumn:
dateForColumn:
dataForColumn:
dataNoCopyForColumn:
UTF8StringForColumn:
objectForColumn:

5.5.2 更新

• 通過調(diào)用- (BOOL)executeUpdate:(NSString*)sql withParameterDictionary:(NSDictionary *)arguments執(zhí)行插入、刪除或者更新數(shù)據(jù)李请。
  插入數(shù)據(jù)或者更新數(shù)據(jù)瞧筛。

NSString *sql = ![rs next] ? INSERT_STATEMENT : UPDATE_STATEMENT;
BOOL success = [db executeUpdate:sql withParameterDictionary:[self pr_toDBDictionary]];
if (!success)
{
    STLogDBLastError(db);
    result = NO;
    return;
}

5.5.3 刪除

• 通過執(zhí)行sql語句刪除

BOOL success = [db executeUpdate:@"DELETE FROM STAppLog WHERE userID = ? AND appLogID = ?;", self.userID, self.appLogID];
if (!success)
{
    STLogDBLastError(db);
    result = NO;
    return;
}

5.5.4 新增

5.6 FMDB 多線程操作數(shù)據(jù)庫

• FMDatabaseQueue內(nèi)部實現(xiàn)了FMDatabase相關(guān)的創(chuàng)建及管理。

FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:aPath];
[queue inDatabase:^(FMDatabase *db) {
    [db executeUpdate:@"INSERT INTO myTable VALUES (?)", @1];
    [db executeUpdate:@"INSERT INTO myTable VALUES (?)", @2];
    [db executeUpdate:@"INSERT INTO myTable VALUES (?)", @3];

    FMResultSet *rs = [db executeQuery:@"select * from foo"];
    while ([rs next]) {
        …
    }
}];

• 執(zhí)行事務(wù)

[queue inTransaction:^(FMDatabase *db, BOOL *rollback) {
    [db executeUpdate:@"INSERT INTO myTable VALUES (?)", @1];
    [db executeUpdate:@"INSERT INTO myTable VALUES (?)", @2];
    [db executeUpdate:@"INSERT INTO myTable VALUES (?)", @3];

    if (whoopsSomethingWrongHappened) {
        *rollback = YES;
        return;
    }

    // etc ...
}];

更多事務(wù)相關(guān)知識參考這篇博客：數(shù)據(jù)庫事務(wù) ios FMDB

5.7 FMDatabase源碼解析

- (BOOL)openWithFlags:(int)flags vfs:(NSString *)vfsName {
#if SQLITE_VERSION_NUMBER >= 3005000
    if (_db) {
        return YES;
    }
    
    int err = sqlite3_open_v2([self sqlitePath], (sqlite3**)&_db, flags, [vfsName UTF8String]);
    if(err != SQLITE_OK) {
        NSLog(@"error opening!: %d", err);
        return NO;
    }
    
    if (_maxBusyRetryTimeInterval > 0.0) {
        // set the handler
        [self setMaxBusyRetryTimeInterval:_maxBusyRetryTimeInterval];
    }
    
    return YES;
#else
    NSLog(@"openWithFlags requires SQLite 3.5");
    return NO;
#endif
}

• vfs是虛擬文件系統(tǒng)的簡稱导盅，主要是用來統(tǒng)一不同平臺操作系統(tǒng)文件的訪問较幌，屏蔽底層硬件介質(zhì)，提供統(tǒng)一的訪問接口白翻。
• 我們可以看到通過 sqlite3_open_v2這個函數(shù)乍炉，在指定的path上面打開了數(shù)據(jù)庫的句柄:_db.
• 后面，我們就可以拿這個句柄去訪問數(shù)據(jù)庫了滤馍，比如創(chuàng)建庫岛琼、創(chuàng)建表、插入數(shù)據(jù)巢株、更新數(shù)據(jù)槐瑞、查詢數(shù)據(jù)等。

5.8 FMResultSet源碼解析

- (FMResultSet *)executeQuery:(NSString *)sql withArgumentsInArray:(NSArray*)arrayArgs orDictionary:(NSDictionary *)dictionaryArgs orVAList:(va_list)args {
    
    // 先判斷這個句柄是否存在阁苞，即操作數(shù)據(jù)庫的入口
    if (![self databaseExists]) {
        return 0x00;
    }
    
    // 是否正在執(zhí)行查詢
    if (_isExecutingStatement) {
        [self warnInUse];
        return 0x00;
    }
    
    _isExecutingStatement = YES;
    
    int rc                  = 0x00;
    
    //定義一個stmt存放結(jié)果集
    sqlite3_stmt *pStmt     = 0x00;
    // 主要是做 銷毀stmt的工作困檩，防止內(nèi)存泄漏
    FMStatement *statement  = 0x00;
    FMResultSet *rs         = 0x00;
    
    if (_traceExecution && sql) {
        NSLog(@"%@ executeQuery: %@", self, sql);
    }
    
    if (_shouldCacheStatements) {
        statement = [self cachedStatementForQuery:sql];
        pStmt = statement ? [statement statement] : 0x00;
        [statement reset];
    }
    
    if (!pStmt) {
        
        rc = sqlite3_prepare_v2(_db, [sql UTF8String], -1, &pStmt, 0);
        
        if (SQLITE_OK != rc) {
            if (_logsErrors) {
                NSLog(@"DB Error: %d \"%@\"", [self lastErrorCode], [self lastErrorMessage]);
                NSLog(@"DB Query: %@", sql);
                NSLog(@"DB Path: %@", _databasePath);
            }
            
            if (_crashOnErrors) {
                NSAssert(false, @"DB Error: %d \"%@\"", [self lastErrorCode], [self lastErrorMessage]);
                abort();
            }
            
            sqlite3_finalize(pStmt);
            _isExecutingStatement = NO;
            return nil;
        }
    }
    
    id obj;
    int idx = 0;
    int queryCount = sqlite3_bind_parameter_count(pStmt); // pointed out by Dominic Yu (thanks!)
    
    // If dictionaryArgs is passed in, that means we are using sqlite's named parameter support
    if (dictionaryArgs) {
        
        for (NSString *dictionaryKey in [dictionaryArgs allKeys]) {
            
            // Prefix the key with a colon.
            NSString *parameterName = [[NSString alloc] initWithFormat:@":%@", dictionaryKey];
            
            if (_traceExecution) {
                NSLog(@"%@ = %@", parameterName, [dictionaryArgs objectForKey:dictionaryKey]);
            }
            
            // Get the index for the parameter name.
            int namedIdx = sqlite3_bind_parameter_index(pStmt, [parameterName UTF8String]);
            
            FMDBRelease(parameterName);
            
            if (namedIdx > 0) {
                // Standard binding from here.
                [self bindObject:[dictionaryArgs objectForKey:dictionaryKey] toColumn:namedIdx inStatement:pStmt];
                // increment the binding count, so our check below works out
                idx++;
            }
            else {
                NSLog(@"Could not find index for %@", dictionaryKey);
            }
        }
    }
    else {
        
        while (idx < queryCount) {
            
            if (arrayArgs && idx < (int)[arrayArgs count]) {
                obj = [arrayArgs objectAtIndex:(NSUInteger)idx];
            }
            else if (args) {
                obj = va_arg(args, id);
            }
            else {
                //We ran out of arguments
                break;
            }
            
            if (_traceExecution) {
                if ([obj isKindOfClass:[NSData class]]) {
                    NSLog(@"data: %ld bytes", (unsigned long)[(NSData*)obj length]);
                }
                else {
                    NSLog(@"obj: %@", obj);
                }
            }
            
            idx++;
            
            [self bindObject:obj toColumn:idx inStatement:pStmt];
        }
    }
    
    if (idx != queryCount) {
        NSLog(@"Error: the bind count is not correct for the # of variables (executeQuery)");
        sqlite3_finalize(pStmt);
        _isExecutingStatement = NO;
        return nil;
    }
    
    FMDBRetain(statement); // to balance the release below
    
    if (!statement) {
        statement = [[FMStatement alloc] init];
        [statement setStatement:pStmt];
        
        if (_shouldCacheStatements && sql) {
            [self setCachedStatement:statement forQuery:sql];
        }
    }
    
    // the statement gets closed in rs's dealloc or [rs close];
    rs = [FMResultSet resultSetWithStatement:statement usingParentDatabase:self];
    [rs setQuery:sql];
    
    NSValue *openResultSet = [NSValue valueWithNonretainedObject:rs];
    [_openResultSets addObject:openResultSet];
    
    [statement setUseCount:[statement useCount] + 1];
    
    FMDBRelease(statement);
    
    _isExecutingStatement = NO;
    
    return rs;
}

5.9 FMDatabaseQueue源碼解析

- (void)inDatabase:(void (^)(FMDatabase *db))block {
#ifndef NDEBUG
    /* Get the currently executing queue (which should probably be nil, but in theory could be another DB queue
     * and then check it against self to make sure we're not about to deadlock. */
    FMDatabaseQueue *currentSyncQueue = (__bridge id)dispatch_get_specific(kDispatchQueueSpecificKey);
    assert(currentSyncQueue != self && "inDatabase: was called reentrantly on the same queue, which would lead to a deadlock");
#endif
    
    FMDBRetain(self);
    
    dispatch_sync(_queue, ^() {
        
        FMDatabase *db = [self database];
        block(db);
        
        if ([db hasOpenResultSets]) {
            NSLog(@"Warning: there is at least one open result set around after performing [FMDatabaseQueue inDatabase:]");
            
#if defined(DEBUG) && DEBUG
            NSSet *openSetCopy = FMDBReturnAutoreleased([[db valueForKey:@"_openResultSets"] copy]);
            for (NSValue *rsInWrappedInATastyValueMeal in openSetCopy) {
                FMResultSet *rs = (FMResultSet *)[rsInWrappedInATastyValueMeal pointerValue];
                NSLog(@"query: '%@'", [rs query]);
            }
#endif
        }
    });
    
    FMDBRelease(self);
}

• FMDatabaseQueue 使用實例

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // 1、查詢所有的日志那槽。
    NSArray *arrLog = [self dd_fetchAppLogs];
});

+ (NSArray *)dd_fetchAppLogs
{
    __block NSMutableArray *appLogs = nil;
    WSELF;
    [[FMDatabaseQueue sharedInstance] inDatabase:^(FMDatabase *db) {
        SSELF;
        FMResultSet *rs = [db executeQuery:@"SELECT * FROM STAppLog;"];
        
        @onExit {
            [rs close];
        };
        
        if (rs == nil)
        {
            STLogDBLastError(db);
            return;
        }
        
        while ([rs next])
        {
            @autoreleasepool {
                if (appLogs == nil) appLogs = [[NSMutableArray alloc] init];
                STAppLog *appLog = [self mj_objectWithKeyValues:rs.resultDictionary];
                [appLogs addObject:appLog];
            }
        }
    }];
    
    return appLogs;
}

6. CoreData

6.1 創(chuàng)建數(shù)據(jù)庫表

• 在MesaSQLite設(shè)計器中創(chuàng)建表結(jié)構(gòu)悼沿，然后將生成的sql復(fù)制出來使用。這樣可以避免手敲代碼產(chǎn)生的錯誤骚灸。
• 將sql保存成文件糟趾，然后放到xcode工程中。

coredata結(jié)構(gòu)

6.2 數(shù)據(jù)模型管理類NSManagedObjectModel

• 通過NSManagedObjectModel甚牲，可以將創(chuàng)建的數(shù)據(jù)模型文件讀取為模型管理類對象义郑。實體類似于數(shù)據(jù)庫中的表結(jié)構(gòu)。

• 創(chuàng)建NSManagedObjectModel對象

• 首先丈钙、我們需要知道數(shù)據(jù)模型文件在哪魔慷，通過數(shù)據(jù)模型文件加載NSManagedObjectModel。

- (NSManagedObjectModel *)managedObjectModel
{
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    
    NSURL *modelURL = [DDBITrackKitBUNDLE URLForResource:@"Model" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

6.3 持久化存儲協(xié)調(diào)者類NSPersistentStoreCoordinator

• NSManagedObjectContext是進行數(shù)據(jù)管理的核心類著恩，我們通過這個類來進行數(shù)據(jù)的增刪改查等操作院尔。
• PersistentStoreCoordinator對象的創(chuàng)建需要用到ManagedObjectModel對象蜻展，根據(jù)objectModel的模型結(jié)構(gòu)創(chuàng)建持久化的本地存儲。同時PersistentStoreCoordinator對象需要知道數(shù)據(jù)庫文件在哪里邀摆，以便打開對一個的數(shù)據(jù)庫纵顾。

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }
    
    // 指定一個數(shù)據(jù)庫文件路徑
    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"DDBITrackKit.sqlite"];
    
    NSError *error = nil;
    // 通過ManagedObjectModel對象創(chuàng)建NSPersistentStoreCoordinator對象。
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    
    // 指定底層的存儲方式為SQLite數(shù)據(jù)庫栋盹。
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        //
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    
    return _persistentStoreCoordinator;
}

6.4 數(shù)據(jù)對象管理上下文NSManagedObjectContext

• 創(chuàng)建NSManagedObjectContext對象

操作數(shù)據(jù)需要用到Object的句柄施逾，每個句柄管理了對應(yīng)的ObjectModel對象。一般我們會創(chuàng)建一個主句柄例获。然后使用子句柄執(zhí)行多線程操作汉额。
需要注意的點是：各個線程創(chuàng)建的子句柄相互之間是不能直接進行通信的，后果是有可能會崩潰榨汤，以及查詢不出數(shù)據(jù)蠕搜、或者查詢出來錯誤的數(shù)據(jù)。如果需要通信收壕，那么需要把實體（Entity）的ObjectID傳遞給另一個線程妓灌，然后這個線程里的context執(zhí)行對應(yīng)的查詢，然后再改變查詢出來的object的數(shù)據(jù)蜜宪。比較繁瑣虫埂。
保存數(shù)據(jù)的時候∑匝椋可以調(diào)用子句柄的save:函數(shù)掉伏，然后會在我們的通知中心里拿到這個數(shù)據(jù)改變的通知。

• 創(chuàng)建主句柄

- (NSManagedObjectContext *)mainManagedObjectContext
{
    if (_mainManagedObjectContext != nil) {
        return _mainManagedObjectContext;
    }
    _mainManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    _mainManagedObjectContext.persistentStoreCoordinator = [self persistentStoreCoordinator];
    return _mainManagedObjectContext;
}

• 創(chuàng)建多線程的子句柄

- (NSManagedObjectContext *)privateContext
{
    // 設(shè)置一個 persistent store coordinator 和兩個獨立的 contexts 被證明了是在后臺處理 Core Data 的好方法澳窑。
    NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    context.persistentStoreCoordinator = [self persistentStoreCoordinator];
    return context;
}

• 創(chuàng)建數(shù)據(jù)更改的通知

[[NSNotificationCenter defaultCenter] addObserverForName:NSManagedObjectContextDidSaveNotification object:nil queue:nil usingBlock:^(NSNotification *note) {
        NSManagedObjectContext *moc = self.mainManagedObjectContext;
        if (note.object != moc) {
            [moc performBlock:^{
                [moc mergeChangesFromContextDidSaveNotification:note];
            }];
        }
    }];

6.5 查詢數(shù)據(jù)

• 通過NSEntityDescription來查詢所需要的實體對象斧散。

+ (instancetype)findOrCreateWithIdentifier:(id)identifier inContext:(NSManagedObjectContext *)context
{
    id object = nil;
    NSString *entityName = NSStringFromClass(self);
    if (identifier)
    {
        NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:entityName];
        fetchRequest.predicate = [NSPredicate predicateWithFormat:@"appLogID = %@", identifier];
        fetchRequest.fetchLimit = 1;
        fetchRequest.returnsObjectsAsFaults = NO;
        NSError *error = nil;
        id object = [[context executeFetchRequest:fetchRequest error:&error] lastObject];
        if (object == nil) {
            object = [NSEntityDescription insertNewObjectForEntityForName:entityName inManagedObjectContext:context];
        }
    }
    else
    {
        object = [NSEntityDescription insertNewObjectForEntityForName:entityName inManagedObjectContext:context];
    }
    
    return object;
}

+ (NSArray *)dd_fetchAllAppLog
{
    NSManagedObjectContext *context = [DatabaseHelper shareInstance].store.privateContext;
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"DDBILog"];
    [request setReturnsObjectsAsFaults:NO];
    NSError *error;
    NSArray *arrResult = [context executeFetchRequest:request error:&error];
    return arrResult;
}

6.6 更新數(shù)據(jù)

• 先查詢出來對象，然后更新對象響應(yīng)的字段照捡，最后調(diào)用save函數(shù)進行保存

- (void)dd_saveOrUpdateWithContext:(NSManagedObjectContext *)localContext completion:(DatabaseCompletion)completion
{
    DDBILog *tAppLog = [DDBILog findOrCreateWithIdentifier:self.appLogID inContext:localContext];
    tAppLog.accuracy         = self.accuracy;
    [localContext save:NULL];
    
    if (completion) {
        completion(YES, nil);
    }
}

6.7 刪除對象

- (void)dd_delete:(DatabaseCompletion)completion
{
    NSManagedObjectContext *localContext = [DatabaseHelper shareInstance].store.privateContext;
    [self dd_deleteWithContext:localContext completion:completion];
}

- (void)dd_deleteWithContext:(NSManagedObjectContext *)context completion:(DatabaseCompletion)completion
{
    [self MR_deleteEntityInContext:context];
    [context save:NULL];
}

7. WCDB