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client-server syncing methodology [theoretical]

- by Kenneth Ballenegger

I'm in the progress of building an web-app that syncs with an iOS client. I'm currently tackling trying to figure out how to go about about syncing. I've come up with following two directions: I've got a fairly simple server web-app with a list of items. They are ordered by date modified and as such syncing the order does not matter. One direction I'm considering is to let the client deal with syncing. I've already got an API that lets the client get the data, as well as do certain actions on it, such as update, add or remove single items. I was considering: 1) on each sync asking the server for all items modified since the last successful sync and updating the local records based on what's returned by the server, and 2) building a persistent queue of create / remove / update requests on the client, and keeping them until confirmation by the server. The risk with this approach is that I'm basically asking each side to send changes to the other side, hoping it works smoothly, but risking a diversion at some point. This would probably be more bandwidth-efficient, though. The other direction I was considering was a more traditional model. I would have a "sync" process in which the client would send its whole list to the server (or a subset since last modified sync), the server would update the data on the server (by fixing conflicts by keeping the last modified item, and keeping deleted items with a deleted = 1 field), and the server would return an updated list of items (since last successful sync) which the client would then replace its data with. Thoughts?

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Perl: Process Communcation

- by Shiftbit

Can anyone explain how I can successfully get my process communicating. I find the perldoc on IPC confusing. What I have so far is: $| = 1; $SIG{CHLD} = {wait}; my $parentPid = $$; if ($pid = fork();) ) { if ($pid == 0) { pipe($parentPid, $$); open PARENT, "<$parentPid"; while (<PARENT>) { print $_; } close PARENT; exit(); } else { pipe($parentPid, $pid); open CHILD, ">$pid"; or error("\nError opening: childPid\nRef: $!\n"); open (FH, "<list") or error("\nError opening: list\nRef: $!\n"); while(<FH>) { print CHILD, $_; } close FH or error("\nError closing: list\nRef: $!\n"); close CHILD or error("\nError closing: childPid\nRef: $!\n); } else { error("\nError forking\nRef: $!\n"); } First Question is what does Perldoc pipe mean by READHANDLE, WRITEHANDLE? Second Questions is can I implement a solution without relying on CPAN or other modules?

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Java - Class type from inside static initialization block

- by DutrowLLC

Is it possible to get the class type from inside the static initialization block? This is a simplified version of what I currently have:: class Person extends SuperClass { String firstName; static{ // This function is on the "SuperClass": // I'd for this function to be able to get "Person.class" without me // having to explicitly type it in but "this.class" does not work in // a static context. doSomeReflectionStuff(Person.class); // IN "SuperClass" } } This is closer to what I am doing, which is to initialize a data structure that holds information about the object and its annotations, etc... Perhaps I am using the wrong pattern? public abstract SuperClass{ static void doSomeReflectionStuff( Class<?> classType, List<FieldData> fieldDataList ){ Field[] fields = classType.getDeclaredFields(); for( Field field : fields ){ // Initialize fieldDataList } } } public abstract class Person { @SomeAnnotation String firstName; // Holds information on each of the fields, I used a Map<String, FieldData> // in my actual implementation to map strings to the field information, but that // seemed a little wordy for this example static List<FieldData> fieldDataList = new List<FieldData>(); static{ // Again, it seems dangerous to have to type in the "Person.class" // (or Address.class, PhoneNumber.class, etc...) every time. // Ideally, I'd liken to eliminate all this code from the Sub class // since now I have to copy and paste it into each Sub class. doSomeReflectionStuff(Person.class, fieldDataList); } }

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How do I use foreach with QDomNodeList in Qt?

- by Venemo

Hi Everyone, I'm new to Qt and I'm learning something new every day. Currently, I'm developing a small application for my Nokia N900 in my free time. Everything is fine, I am able to compile and run Maemo applications on the device. I've just learned about the foreach keyword in Qt. (I know it is not in C++, so I didn't think about it until I accidentally stumbled upon a Qt doc that mentioned it.) So, I decided to change my quite annoying and unreadable loops to foreach, but I failed with this: QDomNodeList list = doc.lastChild().childNodes().at(1).firstChild().childNodes(); for (int x = 0; x < list.count(); x++) { QDomElement node = list.at(x).toElement(); // Do something with node } This is how I tried: foreach (QDomElement node, doc.lastChild().childNodes().at(1).firstChild().childNodes()) { // Do something with node } For some reason the above code doesn't even compile. I get cryptic error messages from the compiler. Could someone please explain to me how to get it right? If the foreach loop doesn't support QDomNodeList, is there a way of handling XML files that do support foreach?

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What is the best way to translate this recursive python method into Java?

- by Simucal

In another question I was provided with a great answer involving generating certain sets for the Chinese Postman Problem. The answer provided was: def get_pairs(s): if not s: yield [] else: i = min(s) for j in s - set([i]): for r in get_pairs(s - set([i, j])): yield [(i, j)] + r for x in get_pairs(set([1,2,3,4,5,6])): print x This will output the desire result of: [(1, 2), (3, 4), (5, 6)] [(1, 2), (3, 5), (4, 6)] [(1, 2), (3, 6), (4, 5)] [(1, 3), (2, 4), (5, 6)] [(1, 3), (2, 5), (4, 6)] [(1, 3), (2, 6), (4, 5)] [(1, 4), (2, 3), (5, 6)] [(1, 4), (2, 5), (3, 6)] [(1, 4), (2, 6), (3, 5)] [(1, 5), (2, 3), (4, 6)] [(1, 5), (2, 4), (3, 6)] [(1, 5), (2, 6), (3, 4)] [(1, 6), (2, 3), (4, 5)] [(1, 6), (2, 4), (3, 5)] [(1, 6), (2, 5), (3, 4)] This really shows off the expressiveness of Python because this is almost exactly how I would write the pseudo-code for the algorithm. I especially like the usage of yield and and the way that sets are treated as first class citizens. However, there in lies my problem. What would be the best way to: 1.Duplicate the functionality of the yield return construct in Java? Would it instead be best to maintain a list and append my partial results to this list? How would you handle the yield keyword. 2.Handle the dealing with the sets? I know that I could probably use one of the Java collections which implements that implements the Set interface and then using things like removeAll() to give me a set difference. Is this what you would do in that case? Ultimately, I'm looking to reduce this method into as concise and straightforward way as possible in Java. I'm thinking the return type of the java version of this method will likely return a list of int arrays or something similar. How would you handle the situations above when converting this method into Java?

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Which is the best free ide/plugin for struts2?

- by Shahensha

Hello friends, I have just learnt struts 2 and now I have taken up a full fledged project in it. I learnt the basics of struts 2 in Netbeans with it's struts2 plugin. But I am not at all happy with it, as it is very basic and I end up doing most of the work. It is obviously better than plain-vanilla text editor, but still not at all near to what netbeans provides for springs and hibernate. I know because netbeans provides native support for springs and hibernate, it is meant to be better. I don't mind changing my IDE if i get better support for struts2! So my questions are Please list all the free IDEs where native support for struts2 is provided. And if possible please compare them. Please list all the plugins that are available for eclipse for struts2 development. I have heard there are better plugins in eclipse. Also, if there are better plugins in any other IDE (other than netbeans or eclipse of course), please list them giving links. Please give me some tips which I'll need before starting a full blown project in Struts2. I haven't worked on any project on Struts2. I have just finished reading Struts 2 in Action of Manning publications. Thanking you in advance! regards shahensha

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how to handle multiple profiles per user?

- by Scott Willman

I'm doing something that doesn't feel very efficient. From my code below, you can probably see that I'm trying to allow for multiple profiles of different types attached to my custom user object (Person). One of those profiles will be considered a default and should have an accessor from the Person class. Can this be done better? from django.db import models from django.contrib.auth.models import User, UserManager class Person(User): public_name = models.CharField(max_length=24, default="Mr. T") objects = UserManager() def save(self): self.set_password(self.password) super(Person, self).save() def _getDefaultProfile(self): def_teacher = self.teacher_set.filter(default=True) if def_teacher: return def_teacher[0] def_student = self.student_set.filter(default=True) if def_student: return def_student[0] def_parent = self.parent_set.filter(default=True) if def_parent: return def_parent[0] return False profile = property(_getDefaultProfile) def _getProfiles(self): # Inefficient use of QuerySet here. Tolerated because the QuerySets should be very small. profiles = [] if self.teacher_set.count(): profiles.append(list(self.teacher_set.all())) if self.student_set.count(): profiles.append(list(self.student_set.all())) if self.parent_set.count(): profiles.append(list(self.parent_set.all())) return profiles profiles = property(_getProfiles) class BaseProfile(models.Model): person = models.ForeignKey(Person) is_default = models.BooleanField(default=False) class Meta: abstract = True class Teacher(BaseProfile): user_type = models.CharField(max_length=7, default="teacher") class Student(BaseProfile): user_type = models.CharField(max_length=7, default="student") class Parent(BaseProfile): user_type = models.CharField(max_length=7, default="parent")

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Why Spark viewengine renders unnecessary (or unexpected) quotes?

- by Arnis L.

If i add pageBaseType="Spark.Web.Mvc.SparkView" in my web.config (necessary to fix intellisense), somehow it does not render links (probably not only) correctly anymore. This is how it's supposed to look like (and does, if page base type is not specified)= This is how it looks when base type is specified= Chrome source viewer shows identical page source code for both cases= <body> <div class="content"> <div class="navigation"> <a href="/Employee/List">Employees</a> <a href="/Product/List">Products</a> <a href="/Store/List">Stores</a> <div class="navigation_title"> Navigation</div> </div> <div class="main"> <div class="content"> <h2>Employees</h2>Nothing found... <a href="/Employee/Create">Create</a> </div> </div> </div> </body> Developer tools does not= So - why my link gets htmlencoded (if that's what happens)? If it's default behavior, then how to render raw html? Using latest Spark version, rebuilt with Asp.Net Mvc2 RC assemblies.

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Setting up a pc bluetooth server for android

- by Del

Alright, I've been reading a lot of topics the past two or three days and nothing seems to have asked this. I am writing a PC side server for my andriod device, this is for exchanging some information and general debugging. Eventually I will be connecting to a SPP device to control a microcontroller. I have managed, using the following (Android to pc) to connect to rfcomm channel 11 and exchange data between my android device and my pc. Method m = device.getClass().getMethod("createRfcommSocket", new Class[] { int.class }); tmp = (BluetoothSocket) m.invoke(device, Integer.valueOf(11)); I have attempted the createRfcommSocketToServiceRecord(UUID) method, with absolutely no luck. For the PC side, I have been using the C Bluez stack for linux. I have the following code which registers the service and opens a server socket: int main(int argc, char **argv) { struct sockaddr_rc loc_addr = { 0 }, rem_addr = { 0 }; char buf[1024] = { 0 }; char str[1024] = { 0 }; int s, client, bytes_read; sdp_session_t *session; socklen_t opt = sizeof(rem_addr); session = register_service(); s = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM); loc_addr.rc_family = AF_BLUETOOTH; loc_addr.rc_bdaddr = *BDADDR_ANY; loc_addr.rc_channel = (uint8_t) 11; bind(s, (struct sockaddr *)&loc_addr, sizeof(loc_addr)); listen(s, 1); client = accept(s, (struct sockaddr *)&rem_addr, &opt); ba2str( &rem_addr.rc_bdaddr, buf ); fprintf(stderr, "accepted connection from %s\n", buf); memset(buf, 0, sizeof(buf)); bytes_read = read(client, buf, sizeof(buf)); if( bytes_read 0 ) { printf("received [%s]\n", buf); } sprintf(str,"to Android."); printf("sent [%s]\n",str); write(client, str, sizeof(str)); close(client); close(s); sdp_close( session ); return 0; } sdp_session_t *register_service() { uint32_t svc_uuid_int[] = { 0x00000000,0x00000000,0x00000000,0x00000000 }; uint8_t rfcomm_channel = 11; const char *service_name = "Remote Host"; const char *service_dsc = "What the remote should be connecting to."; const char *service_prov = "Your mother"; uuid_t root_uuid, l2cap_uuid, rfcomm_uuid, svc_uuid; sdp_list_t *l2cap_list = 0, *rfcomm_list = 0, *root_list = 0, *proto_list = 0, *access_proto_list = 0; sdp_data_t *channel = 0, *psm = 0; sdp_record_t *record = sdp_record_alloc(); // set the general service ID sdp_uuid128_create( &svc_uuid, &svc_uuid_int ); sdp_set_service_id( record, svc_uuid ); // make the service record publicly browsable sdp_uuid16_create(&root_uuid, PUBLIC_BROWSE_GROUP); root_list = sdp_list_append(0, &root_uuid); sdp_set_browse_groups( record, root_list ); // set l2cap information sdp_uuid16_create(&l2cap_uuid, L2CAP_UUID); l2cap_list = sdp_list_append( 0, &l2cap_uuid ); proto_list = sdp_list_append( 0, l2cap_list ); // set rfcomm information sdp_uuid16_create(&rfcomm_uuid, RFCOMM_UUID); channel = sdp_data_alloc(SDP_UINT8, &rfcomm_channel); rfcomm_list = sdp_list_append( 0, &rfcomm_uuid ); sdp_list_append( rfcomm_list, channel ); sdp_list_append( proto_list, rfcomm_list ); // attach protocol information to service record access_proto_list = sdp_list_append( 0, proto_list ); sdp_set_access_protos( record, access_proto_list ); // set the name, provider, and description sdp_set_info_attr(record, service_name, service_prov, service_dsc); int err = 0; sdp_session_t *session = 0; // connect to the local SDP server, register the service record, and // disconnect session = sdp_connect( BDADDR_ANY, BDADDR_LOCAL, SDP_RETRY_IF_BUSY ); err = sdp_record_register(session, record, 0); // cleanup //sdp_data_free( channel ); sdp_list_free( l2cap_list, 0 ); sdp_list_free( rfcomm_list, 0 ); sdp_list_free( root_list, 0 ); sdp_list_free( access_proto_list, 0 ); return session; } And another piece of code, in addition to 'sdptool browse local' which can verifty that the service record is running on the pc: int main(int argc, char **argv) { uuid_t svc_uuid; uint32_t svc_uuid_int[] = { 0x00000000,0x00000000,0x00000000,0x00000000 }; int err; bdaddr_t target; sdp_list_t *response_list = NULL, *search_list, *attrid_list; sdp_session_t *session = 0; str2ba( "01:23:45:67:89:AB", &target ); // connect to the SDP server running on the remote machine session = sdp_connect( BDADDR_ANY, BDADDR_LOCAL, SDP_RETRY_IF_BUSY ); // specify the UUID of the application we're searching for sdp_uuid128_create( &svc_uuid, &svc_uuid_int ); search_list = sdp_list_append( NULL, &svc_uuid ); // specify that we want a list of all the matching applications' attributes uint32_t range = 0x0000ffff; attrid_list = sdp_list_append( NULL, &range ); // get a list of service records that have UUID 0xabcd err = sdp_service_search_attr_req( session, search_list, \ SDP_ATTR_REQ_RANGE, attrid_list, &response_list); sdp_list_t *r = response_list; // go through each of the service records for (; r; r = r-next ) { sdp_record_t *rec = (sdp_record_t*) r-data; sdp_list_t *proto_list; // get a list of the protocol sequences if( sdp_get_access_protos( rec, &proto_list ) == 0 ) { sdp_list_t *p = proto_list; // go through each protocol sequence for( ; p ; p = p-next ) { sdp_list_t *pds = (sdp_list_t*)p-data; // go through each protocol list of the protocol sequence for( ; pds ; pds = pds-next ) { // check the protocol attributes sdp_data_t *d = (sdp_data_t*)pds-data; int proto = 0; for( ; d; d = d-next ) { switch( d-dtd ) { case SDP_UUID16: case SDP_UUID32: case SDP_UUID128: proto = sdp_uuid_to_proto( &d-val.uuid ); break; case SDP_UINT8: if( proto == RFCOMM_UUID ) { printf("rfcomm channel: %d\n",d-val.int8); } break; } } } sdp_list_free( (sdp_list_t*)p-data, 0 ); } sdp_list_free( proto_list, 0 ); } printf("found service record 0x%x\n", rec-handle); sdp_record_free( rec ); } sdp_close(session); } Output: $ ./search rfcomm channel: 11 found service record 0x10008 sdptool: Service Name: Remote Host Service Description: What the remote should be connecting to. Service Provider: Your mother Service RecHandle: 0x10008 Protocol Descriptor List: "L2CAP" (0x0100) "RFCOMM" (0x0003) Channel: 11 And for logcat I'm getting this: 07-22 15:57:06.087: ERROR/BTLD(215): ****************search UUID = 0000*********** 07-22 15:57:06.087: INFO//system/bin/btld(209): btapp_dm_GetRemoteServiceChannel() 07-22 15:57:06.087: INFO//system/bin/btld(209): ##### USerial_Ioctl: BT_Wake, 0x8003 #### 07-22 15:57:06.097: INFO/ActivityManager(88): Displayed activity com.example.socktest/.socktest: 79 ms (total 79 ms) 07-22 15:57:06.697: INFO//system/bin/btld(209): ##### USerial_Ioctl: BT_Sleep, 0x8004 #### 07-22 15:57:07.517: WARN/BTLD(215): ccb timer ticks: 2147483648 07-22 15:57:07.517: INFO//system/bin/btld(209): ##### USerial_Ioctl: BT_Wake, 0x8003 #### 07-22 15:57:07.547: WARN/BTLD(215): info:x10 07-22 15:57:07.547: INFO/BTL-IFS(215): send_ctrl_msg: [BTL_IFS CTRL] send BTLIF_DTUN_SIGNAL_EVT (CTRL) 10 pbytes (hdl 14) 07-22 15:57:07.547: DEBUG/DTUN_HCID_BZ4(253): dtun_dm_sig_link_up() 07-22 15:57:07.547: INFO/DTUN_HCID_BZ4(253): dtun_dm_sig_link_up: dummy_handle = 342 07-22 15:57:07.547: DEBUG/ADAPTER(253): adapter_get_device(00:02:72:AB:7C:EE) 07-22 15:57:07.547: ERROR/BluetoothEventLoop.cpp(88): pollData[0] is revented, check next one 07-22 15:57:07.547: ERROR/BluetoothEventLoop.cpp(88): event_filter: Received signal org.bluez.Device:PropertyChanged from /org/bluez/253/hci0/dev_00_02_72_AB_7C_EE 07-22 15:57:07.777: WARN/BTLD(215): process_service_search_attr_rsp 07-22 15:57:07.787: INFO/BTL-IFS(215): send_ctrl_msg: [BTL_IFS CTRL] send BTLIF_DTUN_SIGNAL_EVT (CTRL) 13 pbytes (hdl 14) 07-22 15:57:07.787: INFO/DTUN_HCID_BZ4(253): dtun_dm_sig_rmt_service_channel: success=0, service=00000000 07-22 15:57:07.787: ERROR/DTUN_HCID_BZ4(253): discovery unsuccessful! 07-22 15:57:08.497: INFO//system/bin/btld(209): ##### USerial_Ioctl: BT_Sleep, 0x8004 #### 07-22 15:57:09.507: INFO//system/bin/btld(209): ##### USerial_Ioctl: BT_Wake, 0x8003 #### 07-22 15:57:09.597: INFO/BTL-IFS(215): send_ctrl_msg: [BTL_IFS CTRL] send BTLIF_DTUN_SIGNAL_EVT (CTRL) 11 pbytes (hdl 14) 07-22 15:57:09.597: DEBUG/DTUN_HCID_BZ4(253): dtun_dm_sig_link_down() 07-22 15:57:09.597: INFO/DTUN_HCID_BZ4(253): dtun_dm_sig_link_down device = 0xf7a0 handle = 342 reason = 22 07-22 15:57:09.597: ERROR/BluetoothEventLoop.cpp(88): pollData[0] is revented, check next one 07-22 15:57:09.597: ERROR/BluetoothEventLoop.cpp(88): event_filter: Received signal org.bluez.Device:PropertyChanged from /org/bluez/253/hci0/dev_00_02_72_AB_7C_EE 07-22 15:57:09.597: DEBUG/BluetoothA2dpService(88): Received intent Intent { act=android.bluetooth.device.action.ACL_DISCONNECTED (has extras) } 07-22 15:57:10.107: INFO//system/bin/btld(209): ##### USerial_Ioctl: BT_Sleep, 0x8004 #### 07-22 15:57:12.107: DEBUG/BluetoothService(88): Cleaning up failed UUID channel lookup: 00:02:72:AB:7C:EE 00000000-0000-0000-0000-000000000000 07-22 15:57:12.107: ERROR/Socket Test(5234): connect() failed 07-22 15:57:12.107: DEBUG/ASOCKWRP(5234): asocket_abort [31,32,33] 07-22 15:57:12.107: INFO/BLZ20_WRAPPER(5234): blz20_wrp_shutdown: s 31, how 2 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): blz20_wrp_shutdown: fd (-1:31), bta -1, rc 0, wflags 0x0 07-22 15:57:12.107: INFO/BLZ20_WRAPPER(5234): __close_prot_rfcomm: fd 31 07-22 15:57:12.107: INFO/BLZ20_WRAPPER(5234): __close_prot_rfcomm: bind not completed on this socket 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): btlif_signal_event: fd (-1:31), bta -1, rc 0, wflags 0x0 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): btlif_signal_event: event BTLIF_BTS_EVT_ABORT matched 07-22 15:57:12.107: DEBUG/BTL_IFC_WRP(5234): wrp_close_s_only: wrp_close_s_only [31] (31:-1) [] 07-22 15:57:12.107: DEBUG/BTL_IFC_WRP(5234): wrp_close_s_only: data socket closed 07-22 15:57:12.107: DEBUG/BTL_IFC_WRP(5234): wsactive_del: delete wsock 31 from active list [ad3e1494] 07-22 15:57:12.107: DEBUG/BTL_IFC_WRP(5234): wrp_close_s_only: wsock fully closed, return to pool 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): btsk_free: success 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): blz20_wrp_write: wrote 1 bytes out of 1 on fd 33 07-22 15:57:12.107: DEBUG/ASOCKWRP(5234): asocket_destroy 07-22 15:57:12.107: DEBUG/ASOCKWRP(5234): asocket_abort [31,32,33] 07-22 15:57:12.107: INFO/BLZ20_WRAPPER(5234): blz20_wrp_shutdown: s 31, how 2 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): blz20_wrp_shutdown: btsk not found, normal close (31) 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): blz20_wrp_write: wrote 1 bytes out of 1 on fd 33 07-22 15:57:12.107: INFO/BLZ20_WRAPPER(5234): blz20_wrp_close: s 33 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): blz20_wrp_close: btsk not found, normal close (33) 07-22 15:57:12.107: INFO/BLZ20_WRAPPER(5234): blz20_wrp_close: s 32 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): blz20_wrp_close: btsk not found, normal close (32) 07-22 15:57:12.107: INFO/BLZ20_WRAPPER(5234): blz20_wrp_close: s 31 07-22 15:57:12.107: DEBUG/BLZ20_WRAPPER(5234): blz20_wrp_close: btsk not found, normal close (31) 07-22 15:57:12.157: DEBUG/Sensors(88): close_akm, fd=151 07-22 15:57:12.167: ERROR/CachedBluetoothDevice(477): onUuidChanged: Time since last connect14970690 07-22 15:57:12.237: DEBUG/Socket Test(5234): -On Stop- Sorry for bombarding you guys with what seems like a difficult question and a lot to read, but I've been working on this problem for a while and I've tried a lot of different things to get this working. Let me reiterate, I can get it to work, but not using service discovery protocol. I've tried a several different UUIDs and on two different computers, although I only have my HTC Incredible to test with. I've also heard some rumors that the BT stack wasn't working on the HTC Droid, but that isn't the case, at least, for PC interaction.

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Multiple WCF calls for a single ASP.NET page load

- by Rodney Burton

I have an existing asp.net web application I am redesigning to use a service architecture. I have the beginnings of an WCF service which I am able to call and perform functions with no problems. As far as updating data, it all makes sense. For example, I have a button that says Submit Order, it sends the data to the service, which does the processing. Here's my concern: If I have an ASP.NET page that shows me a list of orders (View Orders page), and at the top I have a bunch of drop down lists for order types, and other search criteria which is populated by querying different tables from the database (lookup tables, etc). I am hoping to eventually completely decouple the web application from the DB, and use data contracts to pass information between the BLL, the SOA, and the web app. With that said, how can I reduce the # of WCF calls needed to load my "View Orders" page? I would need to make 1 call get the list of orders, and 1 call for each drop down list, etc because those are populated by individual functions in my BLL. Is it good architecture to create a web service method that returns back a specialized data contract that consists of everything you would need to display a View Orders page, in 1 shot? Something like this pseudocode: public class ViewOrderPageDTO { public OrderDTO[] Orders { get; set; } public OrderTypesDTO[] OrderTypes { get; set; } public OrderStatusesDTO[] OrderStatuses { get; set; } public CustomerListDTO[] CustomerList { get; set; } } Or is it better practice in the page_load event to make 5 or 6 or even 15 individual calls to the SOA to get the data needed to load the page? Therefore, bypassing the need for specialized wcf methods or DTO's that conglomerate other DTO? Thanks for your input and suggestions.

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Linq duplicate removal with a twist

- by Danthar

I got a list that contains al the status items of each order. The problem that i have is that i need to remove all the items of which the status - logdate combination is not the highest. e.g var inputs = new List<StatusItem>(); //note that the 3th id is simply a modifier that adds that amount of secs //to the current datetime, to make testing easier inputs.Add(new StatusItem(123, 30, 1)); inputs.Add(new StatusItem(123, 40, 2)); inputs.Add(new StatusItem(123, 50, 3)); inputs.Add(new StatusItem(123, 40, 4)); inputs.Add(new StatusItem(123, 50, 5)); inputs.Add(new StatusItem(100, 20, 6)); inputs.Add(new StatusItem(100, 30, 7)); inputs.Add(new StatusItem(100, 20, 8)); inputs.Add(new StatusItem(100, 30, 9)); inputs.Add(new StatusItem(100, 40, 10)); inputs.Add(new StatusItem(100, 50, 11)); inputs.Add(new StatusItem(100, 40, 12)); var l = from i in inputs group i by i.internalId into cg select from s in cg group s by s.statusId into sg select sg.OrderByDescending(n => n.date).First() ; This creates a list that returnes me the following: order 123 status 30 date 4/9/2010 6:44:21 PM order 123 status 40 date 4/9/2010 6:44:24 PM order 123 status 50 date 4/9/2010 6:44:25 PM order 100 status 20 date 4/9/2010 6:44:28 PM order 100 status 30 date 4/9/2010 6:44:29 PM order 100 status 40 date 4/9/2010 6:44:32 PM order 100 status 50 date 4/9/2010 6:44:31 PM This is ALMOST correct. However that last line which has status 50 needs to be filtered out as well because it was overruled by status 40 in the historylist. U can tell by the fact that its date is lower then the "last" status-item with the status 40. I was hoping someone could give me some pointers because im stuck.

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Why does the OnDeserialization not fire for XML Deserialization?

- by Jonathan

I have a problem which I have been bashing my head against for the better part of three hours. I am almost certain that I've missed something blindingly obvious... I have a simple XML file: <?xml version="1.0" encoding="utf-8"?> <WeightStore xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Records> <Record actual="150" date="2010-05-01T00:00:00" /> <Record actual="155" date="2010-05-02T00:00:00" /> </Records> </WeightStore> I have a simple class structure: [Serializable] public class Record { [XmlAttribute("actual")] public double weight { get; set; } [XmlAttribute("date")] public DateTime date { get; set; } [XmlIgnore] public double trend { get; set; } } [Serializable] [XmlRoot("WeightStore")] public class SimpleWeightStore { [XmlArrayAttribute("Records")] private List<Record> records = new List<Record>(); public List<Record> Records { get { return records; } } [OnDeserialized()] public void OnDeserialized_Method(StreamingContext context) { // This code never gets called Console.WriteLine("OnDeserialized"); } } I am using these in both calling code and in the class files: using System.Xml.Serialization; using System.Runtime.Serialization; I have some calling code: SimpleWeightStore weight_store_reload = new SimpleWeightStore(); TextReader reader = new StringReader(xml); XmlSerializer deserializer = new XmlSerializer(weight_store.GetType()); weight_store_reload = (SimpleWeightStore)deserializer.Deserialize(reader); The problem is that I am expecting OnDeserialized_Method to get called, and it isn't. I suspect it might have something to do with the fact that it's XML deserialization rather than Runtime deserialization, and perhaps I am using the wrong attribute name, but I can't find out what it might be. Any ideas, folks?

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Pass a data.frame column name to a function

- by Kevin Middleton

I'm trying to write a function to accept a data.frame (x) and a column from it. The function performs some calculations on x and later returns another data.frame. I'm stuck on the best-practices method to pass the column name to the function. The two minimal examples fun1 and fun2 below produce the desired result, being able to perform operations on x$column, using max() as an example. However, both rely on the seemingly (at least to me) inelegant (1) call to substitute() and possibly eval() and (2) the need to pass the column name as a character vector. fun1 <- function(x, column){ do.call("max", list(substitute(x[a], list(a = column)))) } fun2 <- function(x, column){ max(eval((substitute(x[a], list(a = column))))) } df <- data.frame(A = 1:20, B = rnorm(10)) fun1(df, "B") fun2(df, "B") I would like to be able to call the function as fun(df, B), for example. Other options I have considered but have not tried: Pass column as an integer of the column number. I think this would avoid substitute(). Ideally, the function could accept either. with(x, get(column)), but, even if it works, I think this would still require substitute Make use of formula() and match.call(), neither of which I have much experience with. Subquestion: Is do.call() preferred over eval()? Thanks, Kevin

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rich suggestions - why input is null? (seam framework)

- by Cristian Boariu

Hi, I'm trying to build a rich suggestions and i do not understand WHY the input value is null... I mean, why inputText value is not taken when i enter something. The .xhtml code: <h:inputText value="#{suggestion.input}" id="text"> </h:inputText> <rich:suggestionbox id="suggestionBoxId" for="text" tokens=",[]" suggestionAction="#{suggestion.getSimilarSpacePaths()}" var="result" fetchValue="#{result.path}" first="0" minChars="2" nothingLabel="No similar space paths found" columnClasses="center" > <h:column> <h:outputText value="#{result.path}" style="font-style:italic"/> </h:column> </rich:suggestionbox> and action class: @Name("suggestion") @Scope(ScopeType.CONVERSATION) public class Suggestion { @In protected EntityManager entityManager; private String input; public String getInput() { return input; } public void setInput(final String input) { this.input = input; } public List<Space> getSimilarSpacePaths() { List<Space> suggestionsList = new ArrayList<Space>(); if (!StringUtils.isEmpty(input) && !input.equals("/")) { final Query query = entityManager.createNamedQuery("SpaceByPathLike"); query.setParameter("path", input + '%'); suggestionsList = (List<Space>) query.getResultList(); } return suggestionsList; } } So, input beeing null, suggestionList is always empty... Why input's value is not posted?

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How do I simulate "Is In" using Linq2Sql

- by flipdoubt

I often find myself with a list of disconnected Linq2Sql objects or keys that I need to re-select from a Linq2Sql data-context to update or delete in the database. If this were SQL, I would use IS IN in the SQL WHERE clause, but I am stuck with what to do in Linq2Sql. Here is a sample of what I would like to write: public void MarkValidated(IList<int> idsToValidate) { using(_Db.NewSession()) // Instatiates new DataContext { // ThatAreIn <- this is where I am stuck var items = _Db.Items.ThatAreIn(idsToValidate).ToList(); foreach(var item in items) item.Validated = DateTime.Now; _Db.SubmitChanges(); } // Disposes of DataContext } Or: public void DeleteItems(IList<int> idsToDelete) { using(_Db.NewSession()) // Instatiates new DataContext { // ThatAreIn <- this is where I am stuck var items = _Db.Items.ThatAreIn(idsToValidate); _Db.Items.DeleteAllOnSubmit(items); _Db.SubmitChanges(); } // Disposes of DataContext } Can I get this done in one trip to the database? If so, how? Is it possible to send all those ints to the database as a list of parameters and is that more efficient than doing a foreach over the list to select each item one at a time?

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JSF/Seam - new component instance on submit?

- by purecharger

And my confusion with JSF continues. This is a continuation of a question asked yesterday, but I feel it warrants a new question. I have a single seam component that expects a URL parameter to be injected for retrieving a List<String> from a method. This works perfectly on the first navigation to the page. The List is used to display many different selectOneRadio groups that populate a <h:form/>. Now on the submit, I cannot get the URL parameter to be injected or otherwise set on the component! Adding <h:inputHidden/> causes FacesExceptions to be thrown. Then I tried setting the List as an instance variable on the object, and when the subsequent call is made on the submit (which I also do not understand why that is done) I check to see if the variable is non-null: if it isn't, return it. Now I found that a new instance of the component is created on submit!!! getList() called this.toString(): .BeanAction@5fd98420 #### This is when submit is clicked getList() called this.toString(): .BeanAction@22aacbce The component has the following annotations: Stateful @Scope(ScopeType.CONVERSATION) @Name("bean") @Restrict("#{identity.loggedIn}") Can someone explain why there is a new instance of the component created? I'm really not quite sure how to go about handling this. I thought the hidden parameter would work, because that is how I would do it with straight HTML, and I'm a little surprised that its not working for JSF/Seam.

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Best Practice - Removing item from generic collection in C#

- by Matt Davis

I'm using C# in Visual Studio 2008 with .NET 3.5. I have a generic dictionary that maps types of events to a generic list of subscribers. A subscriber can be subscribed to more than one event. private static Dictionary<EventType, List<ISubscriber>> _subscriptions; To remove a subscriber from the subscription list, I can use either of these two options. Option 1: ISubscriber subscriber; // defined elsewhere foreach (EventType event in _subscriptions.Keys) { if (_subscriptions[event].Contains(subscriber)) { _subscriptions[event].Remove(subscriber); } } Option 2: ISubscriber subscriber; // defined elsewhere foreach (EventType event in _subscriptions.Keys) { _subscriptions[event].Remove(subscriber); } I have two questions. First, notice that Option 1 checks for existence before removing the item, while Option 2 uses a brute force removal since Remove() does not throw an exception. Of these two, which is the preferred, "best-practice" way to do this? Second, is there another, "cleaner," more elegant way to do this, perhaps with a lambda expression or using a LINQ extension? I'm still getting acclimated to these two features. Thanks. EDIT Just to clarify, I realize that the choice between Options 1 and 2 is a choice of speed (Option 2) versus maintainability (Option 1). In this particular case, I'm not necessarily trying to optimize the code, although that is certainly a worthy consideration. What I'm trying to understand is if there is a generally well-established practice for doing this. If not, which option would you use in your own code?

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From ASPX to WCF

- by Barguast

I'm hoping someone can advise me on how to solve my networking scenario. Both the client and server are to be C# / .NET based. I basically want to invoke some kind of web service from my client in order to retrieve both binary data (e.g. files) and serialised objects and lists of objects (e.g. database query results). At the moment, I'm using ASPX pages, using the query string to provide parameters and I get back either the binary data, or the binary data of the serialised messages. This affords me a lot of flexbility, and I can choose how to transmit the data, perform simulatanous requests, cancel ongoing requests, etc. Since I can control the serialised format, I can also deserialise lists of objects as they are received which is crucial. My problem isn't a problem as such, but this feels a little hack-ish and I can't help but wonder if there are better ways to go about it. I'm considering moving on to WCF or perhaps another technology to see if it helps. However, I need to know if it helps with my scenarios above that is; Can a WCF method return a list of objects, and can the client receive the items of this list as they arrive as opposed to getting the entire list on completion (i.e. streaming). Does anyone know of any examples of this? Am I likely to get any performance benefits from this? I don't know how well ASPX pages are tuned for this, as it surely isn't their primary purpose. Are there any other approaches I should consider? Thanks for your time spent reading this. I hope you can help.

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Perceptron Classification and Model Training

- by jake pinedo

I'm having an issue with understanding how the Perceptron algorithm works and implementing it. cLabel = 0 #class label: corresponds directly with featureVectors and tweets for m in range(miters): for point in featureVectors: margin = answers[cLabel] * self.dot_product(point, w) if margin <= 0: modifier = float(lrate) * float(answers[cLabel]) modifiedPoint = point for x in modifiedPoint: if x != 0: x *= modifier newWeight = [modifiedPoint[i] + w[i] for i in range(len(w))] w = newWeight self._learnedWeight = w This is what I've implemented so far, where I have a list of class labels in answers and a learning rate (lrate) and a list of feature vectors. I run it for the numbers of iterations in miter and then get the final weight at the end. However, I'm not sure what to do with this weight. I've trained the perceptron and now I have to classify a set of tweets, but I don't know how to do that. EDIT: Specifically, what I do in my classify method is I go through and create a feature vector for the data I'm given, which isn't a problem at all, and then I take the self._learnedWeight that I get from the earlier training code and compute the dot-product of the vector and the weight. My weight and feature vectors include a bias in the 0th term of the list so I'm including that. I then check to see if the dotproduct is less than or equal to 0: if so, then I classify it as -1. Otherwise, it's 1. However, this doesn't seem to be working correctly.

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Django m2m form appearing fields

- by dana

I have a classroom application,and a follow relation. Users can follow each other and can create classrooms.When a user creates a classroom, he can invite only the people that are following him. The Classroom model is a m2m to User table. i have in models. py: class Classroom(models.Model): creator = models.ForeignKey(User) classname = models.CharField(max_length=140, unique = True) date = models.DateTimeField(auto_now=True) open_class = models.BooleanField(default=True) members = models.ManyToManyField(User,related_name="list of invited members") and in models.py of the follow application: class Relations(models.Model): initiated_by = models.ForeignKey(User, editable=False) date_initiated = models.DateTimeField(auto_now=True, editable = False) follow = models.ForeignKey(User, editable = False, related_name = "follow") date_follow = models.DateTimeField(auto_now=True, editable = False) and in views.py of the classroom app: def save_classroom(request, username): if request.method == 'POST': u = User.objects.get(username=username) form = ClassroomForm(request.POST, request.FILES) if form.is_valid(): new_obj = form.save(commit=False) new_obj.creator = request.user r = Relations.objects.filter(initiated_by = request.user) # new_obj.members = new_obj.save() return HttpResponseRedirect('.') else: form = ClassroomForm() return render_to_response('classroom/classroom_form.html', { 'form': form, }, context_instance=RequestContext(request)) i'm using a ModelForm for the classroom form, and the default view, taking in consideration my many to many relation with User table, in the field Members, is a list of all Users in my database. But i only want in that list the users that are in a follow relationship with the logged in user - the one who creates the classroom. How can i do that? Thanks!

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Altering lazy-loaded object's private variables

- by Kevin Pang

I'm running into an issue with private setters when using NHibernate and lazy-loading. Let's say I have a class that looks like this: public class User { public int Foo {get; private set;} public IList<User> Friends {get; set;} public void SetFirstFriendsFoo() { // This line works in a unit test but does nothing during a live run with // a lazy-loaded Friends list Users(0).Foo = 1; } } The SetFirstFriendsFoo call works perfectly inside a unit test (as it should since objects of the same type can access each others private properties). However, when running live with a lazy-loaded Friends list, the SetFirstFriendsFoo call silently fails. I'm guessing the reason for this is because at run-time, the Users(0).Foo object is no longer of type User, but of a proxy class that inherits from User since the Friends list was lazy-loaded. My question is this: shouldn't this generate a run-time exception? You get compile-time exceptions if you try to access another class's private properties, but when you run into a situation like this is looks like the app just ignores you and continues along its way.

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javascript scope problem when lambda function refers to a variable in enclosing loop

- by Stefan Blixt

First question on stackoverflow :) Hope I won't embarrass myself... I have a javascript function that loads a list of albums and then it creates a list item for each album. The list item should be clickable, so I call jQuery's click() with a function that does stuff. I do this in a loop. My problem is that all items seem to get the same click function, even though I try to make a new one that does different stuff in each iteration. Another possibility is that the iteration variable is global somehow, and the function refers to it. Code below. debug() is just an encapsulation of Firebug's console.debug(). function processAlbumList(data, c) { for (var album in data) { var newAlbum = $('<li class="albumLoader">' + data[album].title + '</li>').clone(); var clickAlbum = function() { debug("contents: " + album); }; debug("Album: " + album + "/" + data[album].title); $('.albumlist').append(newAlbum); $(newAlbum).click(clickAlbum); } } Here is a transcript of what it prints when the above function runs, after that are some debug lines caused by me clicking on different items. It always prints "10", which is the last value that the album variable takes (there are 10 albums). Album: 0/Live on radio.electro-music.com Album: 1/Doodles Album: 2/Misc Stuff Album: 3/Drawer Collection Album: 4/Misc Electronic Stuff Album: 5/Odds & Ends Album: 6/Tumbler Album: 7/Bakelit 32 Album: 8/Film Album: 9/Bakelit Album: 10/Slow Zoom/Atomic Heart contents: 10 contents: 10 contents: 10 contents: 10 contents: 10 Any ideas? Driving me up the wall, this is. :) /Stefan

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Can I output/flush data to screen while processing ajax page?

- by Bee

I need to display on my page a list of records pulled from a table. Ajax works fine (I query the database and put all the data inside a on the main page) but if I have lots of records (say 500+) it will hang until data is fully loaded, THEN it will be sent back to the page and correctly displayed. I would like to be able to display the records on the page while getting them, instead of being forced to wait until completion. I am trying with flush(); inside the remote (ajax) page but it still waits until full data is loaded. This is what I currently have inside the ajax page: At the very beginning: @apache_setenv('no-gzip', 1); @ini_set('zlib.output_compression', 0); @ini_set('implicit_flush', 1); for ($i = 0; $i < ob_get_level(); $i++) { ob_end_flush(); } ob_implicit_flush(1); Then whenever I have a echo call: ob_flush(); Now if I load the ajax page alone... it will list the records while reading them from the database. But if I call the same page via Ajax, it will hang and send all the data at once. Any idea? This is the function I use to get the ajax content ('id' is the target , 'url' refers to the ajax page that runs the database query to list the records): function ajax(id,url) { xmlhttp=new XMLHttpRequest(); xmlhttp.open("GET",url,false); xmlhttp.send(null); document.getElementById(id).innerHTML = parseScript(xmlhttp.responseText); }

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Why is curl in Ruby slower than command-line curl?

- by Stiivi

I am trying to download more than 1m pages (URLs ending by a sequence ID). I have implemented kind of multi-purpose download manager with configurable number of download threads and one processing thread. The downloader downloads files in batches: curl = Curl::Easy.new batch_urls.each { |url_info| curl.url = url_info[:url] curl.perform file = File.new(url_info[:file], "wb") file << curl.body_str file.close # ... some other stuff } I have tried to download 8000 pages sample. When using the code above, I get 1000 in 2 minutes. When I write all URLs into a file and do in shell: cat list | xargs curl I gen all 8000 pages in two minutes. Thing is, I need it to have it in ruby code, because there is other monitoring and processing code. I have tried: Curl::Multi - it is somehow faster, but misses 50-90% of files (does not download them and gives no reason/code) multiple threads with Curl::Easy - around the same speed as single threaded Why is reused Curl::Easy slower than subsequent command line curl calls and how can I make it faster? Or what I am doing wrong? I would prefer to fix my download manager code than to make downloading for this case in a different way. Before this, I was calling command-line wget which I provided with a file with list of URLs. Howerver, not all errors were handled, also it was not possible to specify output file for each URL separately when using URL list. Now it seems to me that the best way would be to use multiple threads with system call to 'curl' command. But why when I can use directly Curl in Ruby? Code for the download manager is here, if it might help: Download Manager (I have played with timeouts, from not-setting it to various values, it did not seem help) Any hints appreciated.

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Caching and accessing configuration data in ASP.NET MVC app.

- by Sosh

I'm about to take a look at how to implement internationalisation for an ASP.NET MVC project. I'm looking at how to allow the user to change languages. My initial though is a dropdownlist containing each of the supported langauages. Whoever a few questions have come to mind: How to store the list of supported languages? (e.g. just "en", "English"; "fr", "French" etc.) An xml file? .config files? If I store this in a file I'll have to cache this (at startup I guess). So, what would be best, load the xml data into a list (somehow) and store this list in the System.Web.Cache? Application State? How then to load this data into the view (for display in a dropdown)? Give the view direct access to the cache? Just want to make sure I'm going in the right direction here... Thank you.

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