IOS 数据库（FMDB）--- 源码介绍（FMDBDataBase）

基本操作

NSString* docsdir = [NSSearchPathForDirectoriesInDomains( NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
// 将user.sqlite放到Documents文件夹下，并生成user.sqlite的绝对路径
NSString* dbpath = [docsdir stringByAppendingPathComponent:@"user.sqlite"];
// 根据user.sqlite的绝对路径获取到一个FMDatabase对象，其实就是一个封装了的SQLite数据库对象
FMDatabase* db = [FMDatabase databaseWithPath:dbpath];
// 打开该数据库
[db open];
// 执行SQL语句 - select * from people
FMResultSet *rs = [db 
executeQuery
:@"select * from people"];
// 利用next函数，循环输出结果
while ([rs next]) {
    NSLog(@"%@ %@",
        [rs stringForColumn:@"firstname"], 
        [rs stringForColumn:@"lastname"]);
}
// 关闭该数据库
[db close];

很简单是吧，甚至我觉得上面我写的注释都多余了。确实，FMDB说白了就是对SQLite数据库的C/C++接口进行了一层封装，当然功能也更为强大，比如多线程操作，另外FMDB接口要比原生的SQLite接口简洁很多。下面我们就上面的例子研究下FMDB的基本流程。

FMDBDataBase

1.[FMDatabase databaseWithPath:]---初始化工作

#pragma mark FMDatabase instantiation and deallocation

+ (instancetype)databaseWithPath:(NSString*)aPath {
    return FMDBReturnAutoreleased([[self alloc] initWithPath:aPath]);
}

- (instancetype)init {
    return [self initWithPath:nil];
}

- (instancetype)initWithPath:(NSString*)aPath {
    
    assert(sqlite3_threadsafe()); // whoa there big boy- gotta make sure sqlite it happy with what we're going to do.
    
    self = [super init];
    
    if (self) {
        _databasePath               = [aPath copy];
        _openResultSets             = [[NSMutableSet alloc] init];
        _db                         = nil;
        _logsErrors                 = YES;
        _crashOnErrors              = NO;
        _maxBusyRetryTimeInterval   = 2;
    }
    
    return self;
}

2.[FMDatabase open]－－－打开数据库

sqlite3_open(const char *filename, sqlite3 **ppDb)

该例程打开一个指向 SQLite 数据库文件的连接，返回一个用于其他 SQLite 程序的数据库连接对象。

如果 filename 参数是 NULL 或 ':memory:'，那么 sqlite3_open() 将会在 RAM 中创建一个内存数据库，这只会在 session 的有效时间内持续。

如果文件名 filename 不为 NULL，那么 sqlite3_open() 将使用这个参数值尝试打开数据库文件。如果该名称的文件不存在，sqlite3_open() 将创建一个新的命名为该名称的数据库文件并打开。

- (BOOL)open {
    if (_db) {
        return YES;
    }
    
    int err = sqlite3_open([self sqlitePath], (sqlite3**)&_db );
    if(err != SQLITE_OK) {
        NSLog(@"error opening!: %d", err);
        return NO;
    }
    
    if (_maxBusyRetryTimeInterval > 0.0) {
        // set the handler
        [self setMaxBusyRetryTimeInterval:_maxBusyRetryTimeInterval];
    }
    
    
    return YES;
}

- (void)setMaxBusyRetryTimeInterval:(NSTimeInterval)timeout {
    
    _maxBusyRetryTimeInterval = timeout;
    
    if (!_db) {
        return;
    }
    // 处理的handler设置为FMDBDatabaseBusyHandler这个函数
    if (timeout > 0) {
        sqlite3_busy_handler(_db, &FMDBDatabaseBusyHandler, (__bridge void *)(self));
    }
    else {
        // 不使用任何busy handler处理
        sqlite3_busy_handler(_db, nil, nil);
    }
}

// 注意：appledoc（生成文档的软件）中，对于有具体实现的C函数，比如下面这个函数，
// 是有bug的。所以你在生成文档时，忽略.m文件。
// 该函数就是简单调用sqlite3_sleep来挂起进程
static int FMDBDatabaseBusyHandler(void *f, int count) {
    FMDatabase *self = (__bridge FMDatabase*)f;
    // 如果count为0，表示的第一次执行回调函数
    // 初始化self->_startBusyRetryTime，供后面计算delta使用
    if (count == 0) {
        self->_startBusyRetryTime = [NSDate timeIntervalSinceReferenceDate];
        return 1;
    }
    // 使用delta变量控制执行回调函数的次数，每次挂起50~100ms
    // 所以maxBusyRetryTimeInterval的作用就在这体现出来了
    // 当挂起的时长大于maxBusyRetryTimeInterval，就返回0，并停止执行该回调函数了
    NSTimeInterval delta = [NSDate timeIntervalSinceReferenceDate] - (self->_startBusyRetryTime);
    
    if (delta < [self maxBusyRetryTimeInterval]) {
         // 使用sqlite3_sleep每次当前线程挂起50~100ms
        int requestedSleepInMillseconds = (int) arc4random_uniform(50) + 50;
        int actualSleepInMilliseconds = sqlite3_sleep(requestedSleepInMillseconds); 
        // 如果实际挂起的时长与想要挂起的时长不一致，可能是因为构建SQLite时没将HAVE_USLEEP置为1
        if (actualSleepInMilliseconds != requestedSleepInMillseconds) {
            NSLog(@"WARNING: Requested sleep of %i milliseconds, but SQLite returned %i. Maybe SQLite wasn't built with HAVE_USLEEP=1?", requestedSleepInMillseconds, actualSleepInMilliseconds);
        }
        return 1;
    }
    
    return 0;
}

2.[FMDatabase executeQuery]－－－有结果查询

- (FMResultSet *)executeQuery:(NSString *)sql withArgumentsInArray:(NSArray*)arrayArgs orDictionary:(NSDictionary *)dictionaryArgs orVAList:(va_list)args {
    
    if (![self databaseExists]) {
        return 0x00;
    }
    
    if (_isExecutingStatement) {
        [self warnInUse];
        return 0x00;
    }
    
    _isExecutingStatement = YES;
    
    int rc                  = 0x00;
    sqlite3_stmt *pStmt     = 0x00;
    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;
}

3.[FMDatabase executeQuery]－－－无结果查询

- (BOOL)executeUpdate:(NSString*)sql error:(NSError**)outErr withArgumentsInArray:(NSArray*)arrayArgs orDictionary:(NSDictionary *)dictionaryArgs orVAList:(va_list)args {
    
    if (![self databaseExists]) {
        return NO;
    }
    
    if (_isExecutingStatement) {
        [self warnInUse];
        return NO;
    }
    
    _isExecutingStatement = YES;
    
    int rc                   = 0x00;
    sqlite3_stmt *pStmt      = 0x00;
    FMStatement *cachedStmt  = 0x00;
    
    if (_traceExecution && sql) {
        NSLog(@"%@ executeUpdate: %@", self, sql);
    }
    
    if (_shouldCacheStatements) {
        cachedStmt = [self cachedStatementForQuery:sql];
        pStmt = cachedStmt ? [cachedStmt statement] : 0x00;
        [cachedStmt 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();
            }
            
            if (outErr) {
                *outErr = [self errorWithMessage:[NSString stringWithUTF8String:sqlite3_errmsg(_db)]];
            }
            
            sqlite3_finalize(pStmt);
            
            _isExecutingStatement = NO;
            return NO;
        }
    }
    
    id obj;
    int idx = 0;
    int queryCount = sqlite3_bind_parameter_count(pStmt);
    
    // 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 {
                NSString *message = [NSString stringWithFormat:@"Could not find index for %@", dictionaryKey];
                
                if (_logsErrors) {
                    NSLog(@"%@", message);
                }
                if (outErr) {
                    *outErr = [self errorWithMessage:message];
                }
            }
        }
    }
    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) {
        NSString *message = [NSString stringWithFormat:@"Error: the bind count (%d) is not correct for the # of variables in the query (%d) (%@) (executeUpdate)", idx, queryCount, sql];
        if (_logsErrors) {
            NSLog(@"%@", message);
        }
        if (outErr) {
            *outErr = [self errorWithMessage:message];
        }
        
        sqlite3_finalize(pStmt);
        _isExecutingStatement = NO;
        return NO;
    }
    
    /* Call sqlite3_step() to run the virtual machine. Since the SQL being
     ** executed is not a SELECT statement, we assume no data will be returned.
     */
    
    rc      = sqlite3_step(pStmt);
    
    if (SQLITE_DONE == rc) {
        // all is well, let's return.
    }
    else if (rc == SQLITE_ROW) {
        NSString *message = [NSString stringWithFormat:@"A executeUpdate is being called with a query string '%@'", sql];
        if (_logsErrors) {
            NSLog(@"%@", message);
            NSLog(@"DB Query: %@", sql);
        }
        if (outErr) {
            *outErr = [self errorWithMessage:message];
        }
    }
    else {
        if (outErr) {
            *outErr = [self errorWithMessage:[NSString stringWithUTF8String:sqlite3_errmsg(_db)]];
        }
        
        if (SQLITE_ERROR == rc) {
            if (_logsErrors) {
                NSLog(@"Error calling sqlite3_step (%d: %s) SQLITE_ERROR", rc, sqlite3_errmsg(_db));
                NSLog(@"DB Query: %@", sql);
            }
        }
        else if (SQLITE_MISUSE == rc) {
            // uh oh.
            if (_logsErrors) {
                NSLog(@"Error calling sqlite3_step (%d: %s) SQLITE_MISUSE", rc, sqlite3_errmsg(_db));
                NSLog(@"DB Query: %@", sql);
            }
        }
        else {
            // wtf?
            if (_logsErrors) {
                NSLog(@"Unknown error calling sqlite3_step (%d: %s) eu", rc, sqlite3_errmsg(_db));
                NSLog(@"DB Query: %@", sql);
            }
        }
    }
    
    if (_shouldCacheStatements && !cachedStmt) {
        cachedStmt = [[FMStatement alloc] init];
        
        [cachedStmt setStatement:pStmt];
        
        [self setCachedStatement:cachedStmt forQuery:sql];
        
        FMDBRelease(cachedStmt);
    }
    
    int closeErrorCode;
    
    if (cachedStmt) {
        [cachedStmt setUseCount:[cachedStmt useCount] + 1];
        closeErrorCode = sqlite3_reset(pStmt);
    }
    else {
        /* Finalize the virtual machine. This releases all memory and other
         ** resources allocated by the sqlite3_prepare() call above.
         */
        closeErrorCode = sqlite3_finalize(pStmt);
    }
    
    if (closeErrorCode != SQLITE_OK) {
        if (_logsErrors) {
            NSLog(@"Unknown error finalizing or resetting statement (%d: %s)", closeErrorCode, sqlite3_errmsg(_db));
            NSLog(@"DB Query: %@", sql);
        }
    }
    
    _isExecutingStatement = NO;
    return (rc == SQLITE_DONE || rc == SQLITE_OK);
}