一、FMDB源码结构
我们可以从结构上看出FMDB在共有5个文件组成,其中FMDB.h用于管理其他5个文件,下面分别讲述5个文件的用处
(1)FMDatabase:代表一个单独的SQLite操作实例,数据库通过它增删改查操作;
(2)FMResultSet:代表查询后的结果集;
(3)FMDatabaseQueue:代表串行队列,对多线程操作提供了支持;
(4)FMDatabaseAdditions:本类用于扩展FMDatabase,用于查找表是否存在,版本号等功能;
(5)FMDatabasePool:此方式官方是不推荐使用,代表是任务池,也是对多线程提供了支持。
下面将具体讲述每一个类的核心代码是怎么样的?
二、FMDB源码解析
2.1 FMDatabase源码解析
2.1.1 打开数据库连接
- (BOOL)open;是对SQLite中sqlite3_open()函数的封装使用
下面看一下具体使用
- (BOOL)open {
if (_isOpen) {
return YES;
}
if (_db) {
[self close];
}
// now open database
int err = sqlite3_open([self sqlitePath], (sqlite3**)&_db );
if(err != SQLITE_OK) {
NSLog(@"error opening!: %d", err);
return NO;
}
//当执行这段代码的时候,数据库正在被其他线程访问,就需要给他设置重试时间,
if (_maxBusyRetryTimeInterval > 0.0) {
// set the handler
[self setMaxBusyRetryTimeInterval:_maxBusyRetryTimeInterval];
}
_isOpen = YES;
return YES;
}
//下面我们看一下setMaxBusyRetryTimeInterval的实现方法
- (void)setMaxBusyRetryTimeInterval:(NSTimeInterval)timeout {
_maxBusyRetryTimeInterval = timeout;
if (!_db) {
return;
}
if (timeout > 0) {
sqlite3_busy_handler(_db, &FMDBDatabaseBusyHandler, (__bridge void *)(self));
}
else {
// turn it off otherwise
sqlite3_busy_handler(_db, nil, nil);
}
}
上面是打开数据库连接,上面方法setMaxBusyRetryTimeInterval()设置重试时间,
相当于SQLite中调用int sqlite3_busy_handler(sqlite3*,int()(void,int),void*);
针对int sqlite3_busy_handler(sqlite3*,int()(void,int),void*);该函数
(1)第一个参数:哪个数据库需要设置busy_handler
(2)第二个参数:需要回调的busy handler,调用次函数时,需要传参,是sqlite3_busy_handler第三个参数
(3)第三个参数:int参数代表锁事件,该函数被调用次数,如果返回为0,不会再次访问数据库,返回非0,将不断尝试访问数据库。
当获取不到锁时,会执行回调函数的次数以此来延时,等待其他线程等操作完数据库,这样获得操作数据库。
2.1.2 查询数据库
executeQuery函数是数据库比较重要的方法。
在看实现文件
- (FMResultSet *)executeQuery:(NSString*)sql, ... {
va_list args;
va_start(args, sql);
//整个方法关键是下面一句
id result = [self executeQuery:sql withArgumentsInArray:nil orDictionary:nil orVAList:args];
va_end(args);
return result;
}
从上面可以看出:调用executeQuery函数,实际上是调用
- (FMResultSet *)executeQuery:(NSString )sql withArgumentsInArray:(NSArray)arrayArgs orDictionary:(NSDictionary *)dictionaryArgs orVAList:(va_list)args函数,下面看下此函数的实现方式。
- (FMResultSet *)executeQuery:(NSString *)sql withArgumentsInArray:(NSArray*)arrayArgs orDictionary:(NSDictionary *)dictionaryArgs orVAList:(va_list)args {
//判断数据库是否存在
if (![self databaseExists]) {
return 0x00;
}
//判断数据库是否已经在使用当中
if (_isExecutingStatement) {
[self warnInUse];
return 0x00;
}
_isExecutingStatement = YES;
int rc = 0x00;
sqlite3_stmt *pStmt = 0x00;
FMStatement *statement = 0x00;
FMResultSet *rs = 0x00;
//打印sql语句
if (_traceExecution && sql) {
NSLog(@"%@ executeQuery: %@", self, sql);
}
//获取缓存数据
if (_shouldCacheStatements) {
statement = [self cachedStatementForQuery:sql];
pStmt = statement ? [statement statement] : 0x00;
[statement reset];
}
//没有缓存数据,直接查询数据库
if (!pStmt) {
//对sql语句进行预处理,生成预处理过的“sql语句”pStmt。
rc = sqlite3_prepare_v2(_db, [sql UTF8String], -1, &pStmt, 0);
if (SQLITE_OK != rc) {//出错处理
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
//对dictionaryArgs参数的处理,类似于下面":age"参数形式
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 {//对于arrayArgs参数和不定参数的处理,类似于"?"参数形式
while (idx < queryCount) {
if (arrayArgs && idx < (int)[arrayArgs count]) {
obj = [arrayArgs objectAtIndex:(NSUInteger)idx];
}
else if (args) {//不定参数形式
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) {//如果绑定的参数数目不对,则进行出错处理
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) {//生成FMStatement对象
statement = [[FMStatement alloc] init];
[statement setStatement:pStmt];
//缓存的处理,key为sql语句,值为statement
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;
}
发现上面那个函数有四个参数,看到源码之后,我们一一讲述四个参数:
(1)第一个参数sql:代表我们要查询的sql语句;
(2)第二个参数arrayArgs:代表数组类型的参数,举例如下:
FMResultSet *resultSet = [_db executeQuery:@"SELECT * FROM t_student WHERE age > ?" withArgumentsInArray:@[@25]];
(3)第三个参数dictionaryArgs:代表字典类型的参数,举例如下:
FMResultSet *resultSet = [_db executeQuery:@"SELECT * FROM t_student WHERE age > :age" withParameterDictionary:@{@"age":@25}];
(4)第四个参数args:代表可变类型的参数,举例如下:
FMResultSet *resultSet = [_db executeQuery:@"SELECT * FROM t_student WHERE age > ?",@(20)];
2.1.3 更新数据库
针对FMDB数据库增删改都属于对数据库的更新操作,FMDB通过executeUpdate系列函数来实现对数据库的更新操作。
- (BOOL)executeUpdate:(NSString*)sql, …;系列函数,我们来看一下executeUpdate函数的实现。
- (BOOL)executeUpdate:(NSString*)sql, ... {
va_list args;
va_start(args, sql);
//主要是下面这个函数
BOOL result = [self executeUpdate:sql error:nil withArgumentsInArray:nil orDictionary:nil orVAList:args];
va_end(args);
return result;
}
我们再来看一下红色标出的代码实现,- (BOOL)executeUpdate:(NSString*)sql error:(NSError**)outErr withArgumentsInArray:(NSArray*)arrayArgs orDictionary:(NSDictionary *)dictionaryArgs orVAList:(va_list)args函数实现。
#pragma mark Execute updates
- (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 (SQLITE_INTERRUPT == rc) {
if (_logsErrors) {
NSLog(@"Error calling sqlite3_step. Query was interrupted (%d: %s) SQLITE_INTERRUPT", rc, sqlite3_errmsg(_db));
NSLog(@"DB Query: %@", sql);
}
}
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);
}
我们看完了发现它和executeQuery函数有很多相似的地方,源码标注大家可以看一下executeQuery的标注,也是有几个参数,参数的形式也差不多,就是多了一个error,错误的输出语句。
2.1.4 执行多条sql
一次性来执行多条的sql语句对于数据库来说也是常用的操作。FMDB通过使用executeStatements函数来执行多条sql语句
- (BOOL)executeStatements:(NSString *)sql;系列函数来操作,下面看一下函数实现方式
- (BOOL)executeStatements:(NSString *)sql {
return [self executeStatements:sql withResultBlock:nil];
}
上面通过调用executeStatements函数调用,我们再进一步看executeStatements的实现方式。
- (BOOL)executeStatements:(NSString *)sql withResultBlock:(__attribute__((noescape)) FMDBExecuteStatementsCallbackBlock)block {
int rc;
char *errmsg = nil;
rc = sqlite3_exec([self sqliteHandle], [sql UTF8String], block ? FMDBExecuteBulkSQLCallback : nil, (__bridge void *)(block), &errmsg);
if (errmsg && [self logsErrors]) {
NSLog(@"Error inserting batch: %s", errmsg);
sqlite3_free(errmsg);
}
return (rc == SQLITE_OK);
}
上面函数,发现有SQLite,其实对sqlite3_exec函数的封装,完成对多条sql语句的查找。这样讲可能不是很清晰,举例一下:
//多个SQL执行语句入一个字符串中执行
- (void)executeStatementsTest{
NSString *sql =
@"CREATE TABLE IF NOT EXISTS t_student_tmp (id integer PRIMARY KEY AUTOINCREMENT, name text NOT NULL, age integer NOT NULL);"
"INSERT INTO t_student_tmp (name, age) VALUES ('yixiang', 10);"
"INSERT INTO t_student_tmp (name, age) VALUES ('yixiangXX', 20);";
BOOL success = [_db executeStatements:sql];
if (success) {
NSLog(@"执行成功");
}else{
NSLog(@"执行失败");
}
sql = @"SELECT * FROM t_student;"
"SELECT * FROM t_student_tmp;";
success = [_db executeStatements:sql withResultBlock:^int(NSDictionary *resultsDictionary) {
NSLog(@"%@",resultsDictionary);//查询结果都在resultsDictionary
return 0;
}];
if (success) {
NSLog(@"查询成功");
}else{
NSLog(@"查询失败");
}
}
2.1.6 加解密
在FMDatabase还有一个功能,就是对FMDB进行加解密处理,下面为实现方式
#pragma mark Key routines
- (BOOL)rekey:(NSString*)key {
NSData *keyData = [NSData dataWithBytes:(void *)[key UTF8String] length:(NSUInteger)strlen([key UTF8String])];
return [self rekeyWithData:keyData];
}
- (BOOL)rekeyWithData:(NSData *)keyData {
#ifdef SQLITE_HAS_CODEC
if (!keyData) {
return NO;
}
int rc = sqlite3_rekey(_db, [keyData bytes], (int)[keyData length]);
if (rc != SQLITE_OK) {
NSLog(@"error on rekey: %d", rc);
NSLog(@"%@", [self lastErrorMessage]);
}
return (rc == SQLITE_OK);
#else
#pragma unused(keyData)
return NO;
#endif
}
- (BOOL)setKey:(NSString*)key {
NSData *keyData = [NSData dataWithBytes:[key UTF8String] length:(NSUInteger)strlen([key UTF8String])];
return [self setKeyWithData:keyData];
}
- (BOOL)setKeyWithData:(NSData *)keyData {
#ifdef SQLITE_HAS_CODEC
if (!keyData) {
return NO;
}
int rc = sqlite3_key(_db, [keyData bytes], (int)[keyData length]);
return (rc == SQLITE_OK);
#else
#pragma unused(keyData)
return NO;
#endif
}
FMDB使用setKey:和 setKeyWithData:输入密码和鉴别身份,通过rekey:和rekeyWithData:来清除和密码和设置密码,在上面的源码大家可以发现,也是对sqlite3_key以及sqlite3_rekey函数的封装。
上面就是FMDB中FMDatabase类的主要核心代码,希望大家对FMDatabase认识有个提高。
2.2 FMResultSet
2.2.1 初始化对象
- (instancetype)resultSetWithStatement:(FMStatement )statement usingParentDatabase:(FMDatabase)aDB;
通过上面方法可以看出里面有两个参数
(1)第一个参数:(FMStatement *)statement
该对象是对sqlite3_stmt的进一步封装,在sqlite3_stmt *所表示的内容已经不是我们经常使用过的sql语句啦,而是预处理过的语句。
(2)第二个参数:(FMDatabase*)aDB
代表结果集所拥有的FMDatabase操作对象。
下面看一下初始化对象的实现代码
+ (instancetype)resultSetWithStatement:(FMStatement *)statement usingParentDatabase:(FMDatabase*)aDB {
FMResultSet *rs = [[FMResultSet alloc] init];
[rs setStatement:statement];
[rs setParentDB:aDB];
NSParameterAssert(![statement inUse]);
[statement setInUse:YES]; // weak reference
return FMDBReturnAutoreleased(rs);
}
2.2.2 遍历结果集合
- (BOOL)next;
FMDB通过- (BOOL)next函数完成遍历取结果集合。一起看一下- (BOOL)next;的实现代码
- (BOOL)next {
return [self nextWithError:nil];
}
上面代码可以发现:- (BOOL)next函数是对SQLite中-(BOOL)nextWithError:(NSError **)outErr函数的封装,主要完成对对象的逐行取值的任务。在深入看下nextWithError函数实现。
- (BOOL)nextWithError:(NSError **)outErr {
int rc = sqlite3_step([_statement statement]);
if (SQLITE_BUSY == rc || SQLITE_LOCKED == rc) {
NSLog(@"%s:%d Database busy (%@)", __FUNCTION__, __LINE__, [_parentDB databasePath]);
NSLog(@"Database busy");
if (outErr) {
*outErr = [_parentDB lastError];
}
}
else if (SQLITE_DONE == rc || SQLITE_ROW == rc) {
// all is well, let's return.
}
else if (SQLITE_ERROR == rc) {
NSLog(@"Error calling sqlite3_step (%d: %s) rs", rc, sqlite3_errmsg([_parentDB sqliteHandle]));
if (outErr) {
*outErr = [_parentDB lastError];
}
}
else if (SQLITE_MISUSE == rc) {
// uh oh.
NSLog(@"Error calling sqlite3_step (%d: %s) rs", rc, sqlite3_errmsg([_parentDB sqliteHandle]));
if (outErr) {
if (_parentDB) {
*outErr = [_parentDB lastError];
}
else {
// If 'next' or 'nextWithError' is called after the result set is closed,
// we need to return the appropriate error.
NSDictionary* errorMessage = [NSDictionary dictionaryWithObject:@"parentDB does not exist" forKey:NSLocalizedDescriptionKey];
*outErr = [NSError errorWithDomain:@"FMDatabase" code:SQLITE_MISUSE userInfo:errorMessage];
}
}
}
else {
// wtf?
NSLog(@"Unknown error calling sqlite3_step (%d: %s) rs", rc, sqlite3_errmsg([_parentDB sqliteHandle]));
if (outErr) {
*outErr = [_parentDB lastError];
}
}
if (rc != SQLITE_ROW) {
[self close];
}
return (rc == SQLITE_ROW);
}
2.2.3 获取行列的值
通过查看源码发现有以下几处:
(1)- (int)intForColumnIndex:(int)columnIdx;
(2)- (long)longForColumnIndex:(int)columnIdx;
(3)- (long long int)longLongIntForColumnIndex:(int)columnIdx;
上面三个是根据列的索引获取该列的值。再看三个函数的实现代码
(1)- (int)intForColumnIndex:(int)columnIdx;
- (int)intForColumnIndex:(int)columnIdx {
return sqlite3_column_int([_statement statement], columnIdx);
}
(2)- (long)longForColumnIndex:(int)columnIdx
- (long)longForColumnIndex:(int)columnIdx {
return (long)sqlite3_column_int64([_statement statement], columnIdx);
}
(3)- (long long int)longLongIntForColumnIndex:(int)columnIdx
- (long long int)longLongIntForColumnIndex:(int)columnIdx {
return sqlite3_column_int64([_statement statement], columnIdx);
}
通过上面三个函数,可以发现上面三个函数实际上是对sqlite3_column_ *函数的封装。
(4)- (int)intForColumn:(NSString*)columnName;
(5)- (long)longForColumn:(NSString*)columnName;
(6)- (long long int)longLongIntForColumn:(NSString*)columnName;
上面三个方法是根据列的名称取该列的值。下面看一下三个函数具体实现,只举一个即可,其他都是一样实现方式。
- (int)intForColumn:(NSString*)columnName {
return [self intForColumnIndex:[self columnIndexForName:columnName]];
}
再深入看一下intForColumnIndex实现方式,回到上面啦,(方法(1)看上)。
- (int)intForColumnIndex:(int)columnIdx {
return sqlite3_column_int([_statement statement], columnIdx);
}
2.2.4 获取行中所有元素
- (NSDictionary*)resultDictionary:返回值类型为字典。下面是实现方式:
- (NSDictionary*)resultDictionary {
NSUInteger num_cols = (NSUInteger)sqlite3_data_count([_statement statement]);
if (num_cols > 0) {
NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithCapacity:num_cols];
int columnCount = sqlite3_column_count([_statement statement]);
int columnIdx = 0;
for (columnIdx = 0; columnIdx < columnCount; columnIdx++) {
NSString *columnName = [NSString stringWithUTF8String:sqlite3_column_name([_statement statement], columnIdx)];
id objectValue = [self objectForColumnIndex:columnIdx];
[dict setObject:objectValue forKey:columnName];
}
return dict;
}
else {
NSLog(@"Warning: There seem to be no columns in this set.");
}
return nil;
}
2.2.5 KVC讲解
- (void)kvcMagic:(id)object:FMDB中只能对string类型进行支持
下面是kvcMagic:(id)object实现方式
- (void)kvcMagic:(id)object {
// 使用了KVC,将数据库中的每一行数据对应到每一个对象中,对象的属性要和数据库的列名保持一直。
int columnCount = sqlite3_column_count([_statement statement]);
int columnIdx = 0;
for (columnIdx = 0; columnIdx < columnCount; columnIdx++) {
const char *c = (const char *)sqlite3_column_text([_statement statement], columnIdx);
// check for a null row
if (c) {
NSString *s = [NSString stringWithUTF8String:c];
[object setValue:s forKey:[NSString stringWithUTF8String:sqlite3_column_name([_statement statement], columnIdx)]];
}
}
}
2.3 FMDatabaseQueue
FMDB中比较突出优点就是对多线程的处理,而FMDB中对多线程的支持多亏FMDatabaseQueue类。
2.3.1 初始化队列
- (instancetype)databaseQueueWithPath:(NSString*)aPath
实现代码如下:
+ (instancetype)databaseQueueWithPath:(NSString *)aPath {
FMDatabaseQueue *q = [[self alloc] initWithPath:aPath];
FMDBAutorelease(q);
return q;
}
上面函数调用了- (instancetype)initWithPath:(NSString*)aPath flags:(int)openFlags vfs:(NSString *)vfsName函数实现如下:
- (instancetype)initWithPath:(NSString*)aPath flags:(int)openFlags vfs:(NSString *)vfsName {
self = [super init];
if (self != nil) {
_db = [[[self class] databaseClass] databaseWithPath:aPath];
FMDBRetain(_db);
#if SQLITE_VERSION_NUMBER >= 3005000
BOOL success = [_db openWithFlags:openFlags vfs:vfsName];
#else
BOOL success = [_db open];
#endif
if (!success) {
NSLog(@"Could not create database queue for path %@", aPath);
FMDBRelease(self);
return 0x00;
}
_path = FMDBReturnRetained(aPath);
//生成一个串行队列
_queue = dispatch_queue_create([[NSString stringWithFormat:@"fmdb.%@", self] UTF8String], NULL);
//给串行队列生成一个标识
dispatch_queue_set_specific(_queue, kDispatchQueueSpecificKey, (__bridge void *)self, NULL);
_openFlags = openFlags;
_vfsName = [vfsName copy];
}
return self;
}
2.3.2 串行执行数据库的操作
下面看一段代码
- (void)inDatabase:(void (^)(FMDatabase *db))block {
/* 使用dispatch_get_specific目的来查看当前queue是否是之前我们设定的那个_queue,如是的话,那么使用kDispatchQueueSpecificKey作为参数就这样传给dispatch_get_specific的话,返回的值是不为空,而且返回值应该就是上面initWithPath:函数中绑定的那个FMDatabaseQueue对象。有人说除了当前queue还有可能有其他什么queue?这就是FMDatabaseQueue的用途,你可以创建多个FMDatabaseQueue对象来并发执行不同的SQL语句。
另外为什么要判断是不是当前执行的这个queue呢?是为了防止死锁,防止多线程操作出现死锁!
*/
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");
FMDBRetain(self);
dispatch_sync(_queue, ^() {//串行执行block
FMDatabase *db = [self database];
block(db);
if ([db hasOpenResultSets]) {//调试代码
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);
}
通过上面代码发现,对于一个queue就是一个串行队列,即使你开启多线程,依然是串行执行的。
为了方便大家理解,下面举一个例子:
/**
* FMDatabaseQueue实现多线程的案例
*/
- (void)FMDatabaseQueueMutilThreadTest{
//1、获取数据库文件的路径
NSString *doc = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSString *fileName = [doc stringByAppendingPathComponent:@"students.sqlite"];
//使用queue1
FMDatabaseQueue *queue1 = [FMDatabaseQueue databaseQueueWithPath:fileName];
[queue1 inDatabase:^(FMDatabase *db) {
for (int i=0; i<10; i++) {
NSLog(@"queue1---%zi--%@",i,[NSThread currentThread]);
}
}];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[queue1 inDatabase:^(FMDatabase *db) {
for (int i=11; i<20; i++) {
NSLog(@"queue1---%zi--%@",i,[NSThread currentThread]);
}
}];
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[queue1 inDatabase:^(FMDatabase *db) {
for (int i=20; i<30; i++) {
NSLog(@"queue1---%zi--%@",i,[NSThread currentThread]);
}
}];
});
}
2.3.3 关于事物
对于事物,在数据库中,也是保护数据库的安全一种方式。对于一条sql语句,要么全success,要么全fail。下面是实现代码:
- (void)inTransaction:(void (^)(FMDatabase *db, BOOL *rollback))block {
[self beginTransaction:NO withBlock:block];
}
- (void)beginTransaction:(BOOL)useDeferred withBlock:(void (^)(FMDatabase *db, BOOL *rollback))block {
FMDBRetain(self);
dispatch_sync(_queue, ^() { //串行执行,保证线程安全。
BOOL shouldRollback = NO;
if (useDeferred) {
[[self database] beginDeferredTransaction];// 使用延时性事务
}
else {
[[self database] beginTransaction];// 默认使用独占性事务
}
block([self database], &shouldRollback);//执行block
if (shouldRollback) { //根据shouldRollback判断 判断是否回滚,还是提交。
[[self database] rollback];
}
else {
[[self database] commit];
}
});
FMDBRelease(self);
}
2.4 FMDatabaseAdditions
2.4.1 validateSQL
-(BOOL)validateSQL:(NSString*)sql error:(NSError**)error;通过此方法。校验sql语句是否合法。下面是实现代码
- (BOOL)validateSQL:(NSString*)sql error:(NSError**)error {
sqlite3_stmt *pStmt = NULL;
BOOL validationSucceeded = YES;
int rc = sqlite3_prepare_v2([self sqliteHandle], [sql UTF8String], -1, &pStmt, 0);
if (rc != SQLITE_OK) {
validationSucceeded = NO;
if (error) {
*error = [NSError errorWithDomain:NSCocoaErrorDomain
code:[self lastErrorCode]
userInfo:[NSDictionary dictionaryWithObject:[self lastErrorMessage]
forKey:NSLocalizedDescriptionKey]];
}
}
sqlite3_finalize(pStmt);
return validationSucceeded;
}
2.4.2 其他
columnExists:判断column是否存在;
tableExists:判断表是否存在。
2.5 FMDatabasePool
对于FMDatabasePool,苹果本身并不建议使用,所以我们在这没有必要进行讲解,大家也可以不必追究其内容的实现。
上面就是FMDB源码解析的全部内容,大家主要对2.1,2.2,2.3内容进行详细看就可以啦,2.4和2.5了解即可。希望上面的FMDB源码讲解对大家对FMDB认识有所加强,欢迎大家指正。
我们已经讲完了SQLite和FMDB源码解析,下一篇我们将讲述SQLite和FMDB在使用上的区别。