FMDatabase
FMDatabase用来操作数据库，主要接口
/** Opening a new database connection
The database is opened for reading and writing, and is created if it does not already exist.
@return `YES` if successful, `NO` on error.
@see [sqlite3_open()](http://sqlite.org/c3ref/open.html)
@see openWithFlags:
@see close
*/
- (BOOL)open;
/** Closing a database connection
@return `YES` if success, `NO` on error.
@see [sqlite3_close()](http://sqlite.org/c3ref/close.html)
@see open
@see openWithFlags:
*/
- (BOOL)close;
/** Execute single update statement
This method executes a single SQL update statement (i.e. any SQL that does not return results, such as `UPDATE`, `INSERT`, or `DELETE`. This method employs [`sqlite3_prepare_v2`](http://sqlite.org/c3ref/prepare.html), [`sqlite3_bind`](http://sqlite.org/c3ref/bind_blob.html) to bind values to `?` placeholders in the SQL with the optional list of parameters, and [`sqlite_step`](http://sqlite.org/c3ref/step.html) to perform the update.
The optional values provided to this method should be objects (e.g. `NSString`, `NSNumber`, `NSNull`, `NSDate`, and `NSData` objects), not fundamental data types (e.g. `int`, `long`, `NSInteger`, etc.). This method automatically handles the aforementioned object types, and all other object types will be interpreted as text values using the object's `description` method.
@param sql The SQL to be performed, with optional `?` placeholders.
@param ... Optional parameters to bind to `?` placeholders in the SQL statement. These should be Objective-C objects (e.g. `NSString`, `NSNumber`, etc.), not fundamental C data types (e.g. `int`, `char *`, etc.).
@return `YES` upon success; `NO` upon failure. If failed, you can call `<lastError>`, `<lastErrorCode>`, or `<lastErrorMessage>` for diagnostic information regarding the failure.
@see lastError
@see lastErrorCode
@see lastErrorMessage
@see [`sqlite3_bind`](http://sqlite.org/c3ref/bind_blob.html)
@note This technique supports the use of `?` placeholders in the SQL, automatically binding any supplied value parameters to those placeholders. This approach is more robust than techniques that entail using `stringWithFormat` to manually build SQL statements, which can be problematic if the values happened to include any characters that needed to be quoted.
@note You cannot use this method from Swift due to incompatibilities between Swift and Objective-C variadic implementations. Consider using `<executeUpdate:values:>` instead.
*/
- (BOOL)executeUpdate:(NSString*)sql, ...;
///-------------------------
/// @name Retrieving results
///-------------------------
/** Execute select statement
Executing queries returns an `<FMResultSet>` object if successful, and `nil` upon failure. Like executing updates, there is a variant that accepts an `NSError **` parameter. Otherwise you should use the `<lastErrorMessage>` and `<lastErrorMessage>` methods to determine why a query failed.
In order to iterate through the results of your query, you use a `while()` loop. You also need to "step" (via `<[FMResultSet next]>`) from one record to the other.
This method employs [`sqlite3_bind`](http://sqlite.org/c3ref/bind_blob.html) for any optional value parameters. This properly escapes any characters that need escape sequences (e.g. quotation marks), which eliminates simple SQL errors as well as protects against SQL injection attacks. This method natively handles `NSString`, `NSNumber`, `NSNull`, `NSDate`, and `NSData` objects. All other object types will be interpreted as text values using the object's `description` method.
@param sql The SELECT statement to be performed, with optional `?` placeholders.
@param ... Optional parameters to bind to `?` placeholders in the SQL statement. These should be Objective-C objects (e.g. `NSString`, `NSNumber`, etc.), not fundamental C data types (e.g. `int`, `char *`, etc.).
@return A `<FMResultSet>` for the result set upon success; `nil` upon failure. If failed, you can call `<lastError>`, `<lastErrorCode>`, or `<lastErrorMessage>` for diagnostic information regarding the failure.
@see FMResultSet
@see [`FMResultSet next`](<[FMResultSet next]>)
@see [`sqlite3_bind`](http://sqlite.org/c3ref/bind_blob.html)
@note You cannot use this method from Swift due to incompatibilities between Swift and Objective-C variadic implementations. Consider using `<executeQuery:values:>` instead.
*/
- (FMResultSet * _Nullable)executeQuery:(NSString*)sql, ...;
FMResultSet
表示执行查询sql返回的数据,主要接口
///---------------------------------------
/// @name Iterating through the result set
///---------------------------------------
/** Retrieve next row for result set.
You must always invoke `next` or `nextWithError` before attempting to access the values returned in a query, even if you're only expecting one.
@return `YES` if row successfully retrieved; `NO` if end of result set reached
@see hasAnotherRow
*/
- (BOOL)next;
FMDatabaseQueue
使用FMDatabaseQueue可以保证多线程的读写安全
_queue = dispatch_queue_create([[NSString stringWithFormat:@"fmdb.%@", self] UTF8String], NULL);
- (void)inDatabase:(__attribute__((noescape)) 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);
}
通过代码我们发现FMDatabaseQueue使用串行队列实现了多线程读写安全
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