ios - FMDB:更新时数据库被锁定

Question

我使用 FMDB，当我想返回某些值时使用 FMDatabase，当我不需要时使用 FMDatabaseQueue返回任何值。 当我添加到数据库并使用 FMDatabaseQueue 时，我没有错误(除非我在删除数据库时一开始创建一个新数据库，然后创建[没有要删除的数据库，所以它创建一个新的])。 问题是当我使用相同的 FMDatabaseQueue 更新我的数据库时出现错误:

Unknown error finalizing or resetting statement (5: database is locked)

DB Query: UPDATE traps_table SET dist=34721.853417, dist_to_close_point=35734.768293 WHERE _id=10

当我尝试对数据库文件本身进行查询时，我没有收到任何错误，一切都很顺利。

代码如下:

- (void)updateTrapInDatabase:(FMDatabase*)db distance:(double)distance trapID:(int)trapID distanceToClosePoint:(double)distanceToClosePoint
{
    NSString *statment = [NSString stringWithFormat:@"UPDATE %@ SET %@=?, %@=? WHERE %@=?", TRAP_TABLE, DISTANCE, DISTANCE_TO_CLOSE_POINT, ID];
    BOOL update = [db executeUpdate:statment, @(distance), @(distanceToClosePoint), @(trapID)];
    NSLog(@"Update trapID: %i, success: %@", trapID, update?@"YES":[NSString stringWithFormat:@"NO: %@", [db lastErrorMessage]]);
}

函数引用的代码:

- (void)UpdateDistanceToTrap_currentLocation:(CLLocation*)currentLocation old_location:(CLLocation*)old_location theAzimuth:(double)theAzimuth theSpeed:(double)theSpeed
{
    NSLog(@"UpdateDistanceToTrap()");

    __block double latColumn, lonColumn, idColumn, closePointLatColumn, closePointLonColumn, alarmDistanceColumn;
    __block int _id = -1, alarmDistance = -1;
    __block double distance;
    __block CLLocation *trap_location = nil;

    __block NSString *sqlStatment = [NSString stringWithFormat:@"SELECT * FROM %@", TRAP_TABLE];

    FMResultSet *query = [trapsDB.db executeQuery:sqlStatment];

    if ([query next]) {
        latColumn = [query doubleForColumn:LAT];
        lonColumn = [query doubleForColumn:LON];
        closePointLatColumn = [query doubleForColumn:CLOSE_POINT_LAT];
        closePointLonColumn = [query doubleForColumn:CLOSE_POINT_LON];
        idColumn = [query intForColumn:@"_id"];
        alarmDistanceColumn = [query intForColumn:ALARMDISTANCE];

        do {
            _id = [query intForColumn:@"_id"];
            alarmDistance = [query intForColumn:ALARMDISTANCE];

            if ([old_location distanceFromLocation:currentLocation] > kDISTANCE_THRESHOLD_FOR_CHECK_LOCATIONS) {
                trap_location = [[CLLocation alloc] initWithLatitude:[query doubleForColumn:LAT]
                                                           longitude:[query doubleForColumn:LON]];

                distance = [trap_location distanceFromLocation:currentLocation];

                if (distance < alarmDistance + [ref integerForKey:@"DISTANCE_OFFSET"]) {
                    [trapsDB enterOrOutFromArea_operation:kENTER andTrapID:_id];

                    [self startSaveOnMyLocations:currentLocation.coordinate.latitude
                                             lon:currentLocation.coordinate.longitude
                                            time:CreateDate()
                                           speed:theSpeed
                                         azimuth:theAzimuth
                                          trapID:_id];
                }
                else {
                    if ([trapsDB isEnterToArea_trapID:_id] == kENTER) {
                        [self startPostXml:_id];
                        [trapsDB enterOrOutFromArea_operation:kOUT andTrapID:_id];
                    }
                }
            }
            if ([query doubleForColumn:CLOSE_POINT_LAT] != 0.0 || [query doubleForColumn:CLOSE_POINT_LAT] != 0) {
                trap_location = [[CLLocation alloc] initWithLatitude:[query doubleForColumn:CLOSE_POINT_LAT]
                                                           longitude:[query doubleForColumn:CLOSE_POINT_LON]];

                double distanceToClosePoint = [trap_location distanceFromLocation:currentLocation];

                trap_location = [[CLLocation alloc] initWithLatitude:[query doubleForColumn:LAT]
                                                           longitude:[query doubleForColumn:LON]];

                distance = [trap_location distanceFromLocation:currentLocation];

                [trapsDB updateTrapInDatabase:trapsDB.db distance:distance trapID:_id distanceToClosePoint:distanceToClosePoint];
            }
            else {
                trap_location = [[CLLocation alloc] initWithLatitude:[query doubleForColumn:LAT]
                                                           longitude:[query doubleForColumn:LON]];

                distance = [trap_location distanceFromLocation:currentLocation];

                [trapsDB updateTrapInDatabase:trapsDB.db distance:distance trapID:_id distanceToClosePoint:distance];
            }
        } while ([query next]);
    }
}

我的代码有什么问题吗？

编辑:

TrapService.mm:

- (void)UpdateDistanceToTrap_currentLocation:(CLLocation*)currentLocation old_location:(CLLocation*)old_location theAzimuth:(double)theAzimuth theSpeed:(double)theSpeed;

#define trapsDB     ([SQLiteHandler sharedDatabase])

SQLiteHandler.m:

@property (strong, nonatomic) FMDatabase *db;

- (void)updateTrapInDatabase:(FMDatabase *)db distance:(double)distance trapID:(int)trapID distanceToClosePoint:(double)distanceToClosePoint;

编辑2: 更新了我的固定代码。

Answer 1

您处于 inDatabase 调用中，循环访问 SELECT 语句，然后尝试执行另一个 inDatabase 调用。如果您打算这样做，您可能希望将 FMDatabase 作为参数传递给该方法，而不是再次调用 inDatabase:

- (void)updateTrapInDatabase:(FMDatabase *)db distance:(double)distance trapID:(int)trapID distanceToClosePoint:(double)distanceToClosePoint
{
    NSString *sqlStatment = [NSString stringWithFormat:@"UPDATE %@ SET %@=?, %@=? WHERE %@=?", TRAP_TABLE, DISTANCE, DISTANCE_TO_CLOSE_POINT, ID];

    BOOL update = [db executeUpdate:sqlStatment, @(distance), @(distanceTpClosePoint), @(trapID)];
    NSLog(@"Update trapID: %i, success: %@", trapID, update?@"YES":[NSString stringWithFormat:@"NO: %@", [db lastErrorMessage]]);
}

并将您的调用替换为:

[trapsDB updateTrapDistance:distance andTrapID:_id andDistanceToClosePoint:distanceToClosePoint];

与:

[trapsDB updateTrapInDatabase:db distance:distance trapID:_id distanceToClosePoint:distanceToClosePoint];

(顺便说一句，在 SQL 中使用 ? 占位符通常是谨慎的(避免 float 变量的精度相关问题，避免 SQL 注入(inject)问题和 的引用问题) code>NSString 变量)，所以我还调整了上面的 SQL。此外，如果 SQL 语句失败，我总是记录 lastErrorMessage，否则我只是猜测 SQL 失败的原因。使用或者忽略这些不相关的调整，只要您认为合适。)

但要点是，当已经在 inDatabase 中时，永远不应该调用 inDatabase。但奇怪的是，在已经位于 inDatabase 中时调用 inDatabase 通常会导致死锁，而不是“数据库被锁定”错误。坦率地说，FMDatabaseQueue 的全部目的是协调来自不同线程的数据库请求，以便数据库永远不会繁忙。您通常会收到“数据库已锁定”错误的唯一一次情况是您有多个 FMDatabaseQueue 或 FMDatabase 对象。您的应用在任何给定时间都只能打开一个数据库对象。