I have a graph editor, where user has option to create a node. It gets connected with all currently selected nodes. In google document, it looks like a node (its string label) is mapped to the comma-separated set of connected labels. So, to add a node, I first create an empty map item
map.set(name, "");
and, then, separately add the connected items
if (map.get(a) == null) throw new Error("node " + a + " does not exist") // fails here
if (map.get(b) == null) throw new Error("node " + b + " does not exist")
map.set(a, a_connections)
map.set(b, b_connections)
The problem is that map.get detects that node is not added into the map yet. It takes some time. It seems that the operations are non-blocking even within single JS client (read-my-writes inconsistent). How am I supposed to work with that?
I have noticed this inconsistency when tried to establish two connections (just to detect when connections are failed because it can happen that connection is lost and all my edits do not propagate to server and I wanted to the user to know about that).
This page has some details on conflict resolution and things you can do in order to have your changes be applied together.
I'm a little confused from your example what the problem/expected behavior is.
If you do map.set("foo", "") followed by map.get("foo") on the same client from within the same synchronous block the get will always return what you set.
If you do it from different synchronous blocks, but on the same client, get will return something different only if another client made a change to the value of "foo".
If you are doing the set and get on different clients, then the value of "foo" can take an arbitrary amount of time to propagate to the other client. You should be able to register a listener to discover when it is set.
If you'd like to track when all changes have been persisted, you can listen to DocumentSaveStateChangedEvents
Related
Thanks in advance for attempting to asssist me with this issue.
I'm using CakePHP 2 (2.10.22).
I have a system which creates applications. Each application that gets created has a unique application number. The MySQL database column that stores this application number is set to 'Not null' and 'Unique'. I'm using CakePHP to get the last used application number from the database to then build the next application number for the new application that needs to be created. The process that I have written works without any problem when a single request is received at a given point in time. The problem arises when two requests are received to create an application at the exact same time. The behaviour that I have observed is that the the request that gets picked up first gets the last application number - e.g. ABC001233 and assigns ABC001234 as the application number for the new application it needs to create. It successfully saves this application into the database. The second request which is running concurrently also gets ABC001233 as the last application number and tries to create a new application with ABC001234 as the application number. The MySQL database returns an error saying that the application number is not unique. I then put the second request to sleep for 2 seconds by which time the first application has successfully saved to the database. I then re-attempt the application creation process which first gets the last application number which should be ABC001234 but instead each database read keeps returning ABC001233 even though the first request has long been completed. Both requests have transactions in the controller. What I have noticed is that when I remove these transactions, the process works correctly where for the second request after the first attempt fails, the second attempt works correctly as the system correctly gets ABC001234 as the last application number and assigns ABC001235 as the new application number. I want to know what I need to be doing so as to ensure the process works correctly even with the transaction directives in the controller.
Please find below some basic information on how the code is structured -
Database
The last application number is ABC001233
Controller file
function create_application(){
$db_source->begin(); //The process works correctly if I remove this line.
$result = $Application->create_new();
if($result === true){
$db_source->commit();
)else{
$db_source->rollback();
}
}
Application model file
function get_new_application_number(){
$application_record = $this->find('first',[
'order'=>[
$this->name.'.application_number DESC'
],
'fields'=>[
$this->name.'.application_number'
]
]);
$old_application_number = $application_record[$this->name]['application_number'];
$new_application_number = $old_application_number+1;
return $new_application_number;
}
The above is where I feel the problem originates. For the first request that gets picked up, this find correctly finds that ABC001233 is the last application number and this function then returns ABC001234 as the next application number. For the second request, it also picks up ABC001233 as the last application number but will fail when it tries to save ABC001234 as the application number as the first request has already saved an application with that number. As a part of the second attempt for the second request (which occurs because of the do/while loop) this find is requested again, but instead of returning ABC001234 as the last application number (per the successfuly save of the first request), it keeps returning ABC001233 resulting in a failure to correctly save. If I remove the transaction from the controller, this then works correctly where it will return ABC001234 in the second attempt. I couldn't find any documentation as to why that is and what can be done about the same and is where I need some assistance. Thank you!
function create_new(){
$new_application_number = $this->get_new_application_number();
$save_attempts = 0;
do{
$save_exception = false;
try{
$result = $this->save([$this->name=>['application_number'=>$new_application_number]], [
'atomic'=>false
]);
}catch(Exception $e){
$save_exception = true;
sleep(2);
$new_application_number = $this->get_new_application_number();
}
}while($save_exception === true && $save_attempts++<5);
return !$save_exception;
}
You just have to lock the row with the previous number in a transaction using SELECT ... FOR UPDATE. It's much better than the whole table lock as said in the comments.
According to documentation https://book.cakephp.org/2/en/models/retrieving-your-data.html you just have to add 'lock' => true to get_new_application_number function:
function get_new_application_number(){
$application_record = $this->find('first',[
'order'=>[
$this->name.'.application_number DESC'
],
'fields'=>[
$this->name.'.application_number'
],
'lock'=>true
]);
$old_application_number = $application_record[$this->name]['application_number'];
$new_application_number = $old_application_number+1;
return $new_application_number;
}
How does it work:
The second transaction will wait on that request while the first transaction is ended.
P.S. According to documentation lock option was added in the 2.10.0 version of CakePHP.
I would like to know what the correct place to close a connection to the database is.
Let's say that I have the following piece of code:
function addItem(dbName, versionNumber, storeName, element, callback){
var requestOpenDB = indexedDB.open(dbName, versionNumber); //IDBRequest
requestOpenDB.onsuccess = function(event){
//console.log ("requestOpenDB.onsuccess ");
var db = event.target.result;
var trans = db.transaction(storeName, "readwrite");
var store = trans.objectStore(storeName);
var requestAdd = store.add(element);
requestAdd.onsuccess = function(event) {
callback("Success");
};
requestAdd.onerror = function(event) {
callback("Error");
};
};
requestOpenDB.onerror = function(event) {
console.log ("Error:" + event.srcElement.error.message);/* handle error */
callback("Error");
};
}
addItem basically adds a new element into the database. As per my understanding, when the requestAdd event is triggered that doesn't mean necessarily that the transaction has finished. Therefore I am wondering what the best place to call db.close() is. I was closing the connection inside of requestAdd.onsucess, but if an error happens and requestAdd.onerror is triggered instead, the connection might still be opened. I am thinking about adding trans.oncomplete just under request.onerror and close the db connection here which might be a better option. Any inputs will be more than welcome. Thank you.
You may wish to explicitly close a connection if you anticipate upgrading your database schema. Here's the scenario:
A user opens your site in one tab (tab #1), and leaves it open.
You push an update to your site, which includes code to upgrade the database schema, increasing the version number.
The same user opens a second tab to your site (tab #2) and it attempts to connect to the database.
If the connection is held open by tab #1, the connection/upgrade attempt by tab #2 will be blocked. Tab #1 will see a "versionchange" event (so it could close on demand); if it doesn't close its connection then tab #2 will see a "blocked" event.
If the connection is not held open by tab #1, then tab #2 will be able to connect and upgrade. If tab #1 then tries (based on user action, etc) to open the database (with an explicit version number) it will fail since it will be using an old version number (since it still has the old code).
You generally never need to close a connection. You are not creating memory leaks or anything like that. Leaving the connection open does not result in a material performance hit.
I would suggest not worrying about it.
Also, whether you add trans.oncomplete before or after request.onerror is not important. I understand how it can be confusing, but the order in which you bind the listeners is irrelevant (qualified: from within the same function scope).
You can call db.close() immediately after creating the transaction
var trans = db.transaction(storeName, "readwrite");
db.close();
and it will close the connection only after the transaction has completed.
https://developer.mozilla.org/en-US/docs/Web/API/IDBDatabase/close says
The connection is not actually closed until all transactions created using this connection are complete. No new transactions can be created for this connection once this method is called.
If you want to run multiple versions of your app and both access the same database, you might think it's possible to keep connections open to both. This is not possible. You must close the database on one before opening it on another. But one problem is that there is currently no way to know when the database actually closes.
I'm having a strange issue.
I created a model observer for my user model. The model observer is being run at 'saving'. when I dump the object at the very end of the user model to be displayed ( this is just before it saves.. according to laravel docs ) it displays all the attributes set correctly for the object, I've even seen an error that showed the correct attributes as set and being inserted into my database table. However, after the save has been completed and I query the database, two of the fields are not saved into the table.
There is no code written by myself sitting between the point where I dumped the attributes to check that they had been set and the save operation to the database. so I have no idea what could be causing this to happen. All the names are set correctly, and like I said, the attributes show as being inserted into the database, they just never end up being saved, I receive no error messages and only two out of ten attributes aren't being saved.
In my searches I have found many posts detailing that the $fillable property should be set, or issues relating to a problem with variables being misnamed or unset, however because I already have the specific attributes not being saved specified in the $fillable array, on top of the fact that they print out exactly as expected pre save, I don't believe those issues are related to the problem I am experiencing.
to save I'm calling:
User::create(Input::all());
and then the observer that handles the data looks like this:
class UserObserver {
# a common key between the city and state tables, helps to identify correct city
$statefp = State::where('id',$user->state_id)->pluck('statefp');
# trailing zeros is a function that takes the first parameter and adds zeros to make sure
# that in this case for example, the dates will be two characters with a trailing zero,
# based on the number specified in the second parameter
$user->birth_date = $user->year.'-'.$user->trailingZeros( $user->month, 2 ).'-'.$user->trailingZeros( $user->day, 2 );
if(empty($user->city)){
$user->city_id = $user->defaultCity;
}
$user->city_id = City::where( 'statefp', $statefp )->where('name', ucfirst($user->city_id))->pluck('id');
# if the user input zip code is different then suggested zip code then find location data
# on the input zip code input by the user from the geocodes table
if( $user->zip !== $user->defaultZip ){
$latlon = Geocode::where('zip', $user->zip)->first();
$user->latitude = $latlon['latitude'];
$user->longitude = $latlon['longitude'];
}
unset($user->day);
unset($user->month);
unset($user->year);
unset($user->defaultZip);
unset($user->defaultCity);
}
that is the code for the two values that aren't being set, when I run
dd($user);
all the variables are set correctly, and show up in the mysql insert attempt screen with correct values, but they do not persist past that point.. it seems to me that possibly mysql is rejecting the values for the city_id and the birth_date. However, I cannot understand why, or whether it is a problem with Laravel or mysql.
since I was calling
User::create();
I figured I'd try to have my observer listen to:
creating();
I'm not sure why it only effected the date and city variables, but changing the function to listen at creating() instead of saving() seems to have solved my problem.
I recently started a new job with a company and my first task is to update some quite old software for them.
There is a big back story but basically the software was written in PB8 (around 1997) and no one within the company (including me) has had any experience with PowerBuilder before and as the newbie I have been tasked to update and maintain it until a replacement has been approved and can be developed.
We have the license for PowerBuilder 12.5 so I am using PB12.5 Classic to do everything. The original developer cannot be contacted for support and no documentation exists.
One thing I am trying to understand, that will be a huge help in the future, is how to determine where functions are defined and where variables get their values..
The example I am working on at the moment is the following scenario.
There is a data window with tabs, named tab_detail each tab displays different whatever little orange men are in the tree list.
One of these are called dw_detail which allows pasting of data. None of the other tabs allow pasting of data, but I would like them to. dw_detail has an event rbuttondown() with the following code in it:
Window w_parentwin
If ib_add_mode Or ib_chg_mode Then
w_parentwin = Parent.GetParent().GetParent()
m_dwpaste m_pop_paste
m_pop_paste = CREATE m_dwpaste
m_pop_paste.idw_data = This
If ii_agent_code > 0 And Not IsNull(id_period) And Clipboard() <> "" Then
m_pop_paste.m_popup.m_paste.Enabled = TRUE
Else
m_pop_paste.m_popup.m_paste.Enabled = FALSE
End If
m_pop_paste.m_popup.PopMenu(w_parentwin.PointerX(), w_parentwin.PointerY())
DESTROY(m_pop_paste)
End If
When I add that code to the rbuttondown() event of tab number 2 (dw_adjustment) tab 2 now allows paste when I right click within the dw_adjustment data window but the data gets pasted to the fields within the dw_detail tab not the fields on the dw_adjustment tab.
I have tried debugging and stepping through the code but there are thousands of values in the variable window and without the ability to search I cannot find the variables used above and what their values are or why data gets pasted to the dw_detail tab instead of the dw_adjustment tab when I paste into the dw_adjustment tab.
Basically I am looking for any helpful tips on where to look or what the above is doing and why everything pastes to tab 1 instead of the tab I clicked paste in.
If more detail is needed from code from a different location or more information is needed I am happy to provide it.
As suggested by Seki I found the m_popup when double clicked it came up with wf_pastereturn():
Integer li_idx, li_rows, li_dwrows, li_comm, li_seqno
String ls_approval_type
If tab_detail.tabpage_details.dw_detail.RowCount() > 0 Then
li_idx = 1
li_dwrows = tab_detail.tabpage_details.dw_detail.RowCount()
Do Until li_idx > li_dwrows
ls_approval_type = tab_detail.tabpage_details.dw_detail.Object.approval_type [li_idx]
If IsNull(ls_approval_type) or ls_approval_type = "" Then
tab_detail.tabpage_details.dw_detail.DeleteRow(li_idx)
Else
li_idx++
End If
li_dwrows = tab_detail.tabpage_details.dw_detail.RowCount()
Loop
End If
If li_dwrows > 0 Then
li_seqno = Long(tab_detail.tabpage_details.dw_detail.Object.seq_no [li_dwrows])
End If
li_seqno += 10
If Clipboard() <> "" Then
If tab_detail.tabpage_details.dw_detail.ImportClipboard(1, li_rows, 1, 4, 3) <= 0 Then
MessageBox("Invalid Data", "Unable to paste!", StopSign!)
Return -1
End If
li_rows = tab_detail.tabpage_details.dw_detail.RowCount()
li_dwrows++
For li_idx = li_dwrows To li_rows
tab_detail.tabpage_details.dw_detail.Object.approval_type [li_idx] = trim(tab_detail.tabpage_details.dw_detail.Object.approval_type [li_idx])
tab_detail.tabpage_details.dw_detail.Object.approval_no [li_idx] = trim(tab_detail.tabpage_details.dw_detail.Object.approval_no [li_idx])
tab_detail.tabpage_details.dw_detail.Object.agent_code [li_idx] = ii_agent_code
tab_detail.tabpage_details.dw_detail.Object.period [li_idx] = id_period
li_comm = f_new_commission(Long(tab_detail.tabpage_details.dw_detail.Object.value_of_work[li_idx]), id_period)
tab_detail.tabpage_details.dw_detail.Object.levy_payable[li_idx]= &
inv_rate.of_CalculateLevyPayable (Long(tab_detail.tabpage_details.dw_detail.Object.value_of_work[li_idx]), id_period)
tab_detail.tabpage_details.dw_detail.Object.comm_deductable [li_idx] = li_comm
tab_detail.tabpage_details.dw_detail.Object.commission [li_idx] = li_comm
tab_detail.tabpage_details.dw_detail.Object.seq_no [li_idx] = li_seqno
li_seqno += 10
tab_detail.tabpage_details.dw_detail.Object.agent_return_detail_create_date[li_idx] = Today()
tab_detail.tabpage_details.dw_detail.Object.agent_return_detail_create_user[li_idx] = SQLCA.Logid
Next
Clipboard("")
Return 0
Else
Return -1
End If
I modified the function to use the windows SelectedTab property. Data will now paste into the tab but in the wrong input fields. I looked further and the data columns for the ImportClipboard function do not line up.
How is the best way to change the order of the selected database columns?
Here is a screenshot of what I mean by tabs:
So within the main program window, there are the above tabs, within each tab (where the input fields are) there is a data window labelled with the dw_ prefix.
Thanks heaps for your help.
I think first you should do some short tutorials. Please check out these:
PowerBuilder Classic 12/12.5 guide/tutorials
These are short and useful.
On the other side you are able to select specific variables in your own "watch variable" list, so you do not have to search over the several variables. You can right click on the variable name and do a Quickwatch or you can Insert the variable name in the Watch window.
Br. Gábor
The action with a contextual menu is in 2 times :
handle the mouse right click to display a contextual menu
perform an action among the one or several actions provided by the popup menu
You shown the pbscript that is displaying the menu with PopMenu() if there is something in the clipboard (Clipboard() <> "") and maybe you did not noticed that the pasting action is somewhere else.
Look in m_popup: there must be some code inside that may be hard-coded to paste in dw_detail. If so, maybe that you could store in the window instance variables a reference to the currently processed dw for the contextual menu.
Something like :
datawindow idw_current in the instance variables
then in the rbuttondown() event idw_current = this (this being the datawindow the rbuttondown() event belongs to)
and finally in the menu reuse the id_current instead of a hardcoded dw_detail
Concerning your question about where the variables are modified: what you can do is searching the variables by their name (right click on the target or a single pbl or object then 'search'), and put a breakpoint on the lines where they are affected. If you run in debug mode (CtrlDCtrlT instead of CtrlR) you will be able to trace when a variable is modified.
Paste Problem
Pass 1
It's hard to tell for sure, but I'd look at the code of m_dwpaste.m_popup.m_paste.Clicked. The worse case scenario is that dw_detail is hard coded into that script; the slightly better case is that it has a more flexible routine in there, but somehow dw_adjustment doesn't fit into that algorithm.
Pass 2
With the new information, we can see that the code of wf_pastereturn() (I'm not sure how you got to this script, but this looks like the culprit) is not simply pasting, but doing a lot more that involves specific fields. In fact, it's not just pasting, it's importing the data, which means that it's assuming the contents of the clipboard are not only in a specific format, but match the data set of the DataWindow (see the Columns pane in the DW painter, and be careful not to confuse the data set part of the DataWindow with the UI part). The question is, do you want:
"Pasting" like copying text from Notepad into a browser form; just putting text into the current field?
"Pasting" exactly like the other DataWindow, including assumptions that all the same columns mentioned in the script are in both DataWindows?
"Pasting" something like this script, but customized for the data set in the new DataWindow?
These all require somewhat different solutions, combined with the differences I asked about in my comment about tabs vs. DataWindows.
Finding Stuff
I'm going to give an unapologetically biased point of view, because I'm the author of a tool that, among other things, helps you search PowerBuilder code called PBL Peeper.
If you're looking at code in the Browse tab, and you want to see other mentions of the variable, you can select it, right click, and either
search forward or back within the script
search for the object name in the tree on the left (it'll make more sense when you see it)
search either the rest of the object or the rest of the application
Finding where a variable is assigned is more difficult than it sounds, because of the multiple syntaxes that could be involved.
// assigns a value on instantiation
int i = 1
// assigns a value when executed
i = 1
// does not assign a value
IF i = 1 THEN
// assigns a value possibly if the parameter is passed by reference (kind of like a pointer to the variable)
f_foo (i)
Finding the setting of a variable can be helped by understanding variable scope. If the variable is local, you only need to search the script. If the scope is instance or shared, you need to search the object (as above, pretty easy) and its descendants (easy to go to a given descendant with an RMB on the treeview, harder to search on a set of descendants). If the scope is global, you want to search the entire app.
Finding where a selected function is declared is possible, but you need to know a little secret (or RTFM). The Find on the RMB menu uses the parameters from the Find page, so you need to set Portion Type to All, not just Scripts, to find where functions are declared. Alternatively, you can use the Lists / Scripts pages and find the script using the functions on that page (Find, QuickFind, Filter, etc...).
The tool has a plethora of functionalities that let you find, filter and sift through code to get at what you're after. The above is just a quick introduction.
Good luck,
Terry.
I have a view ObjectDisplay that is composed of two relevant tables: Object and State. State represents the state of an Object, and the view pulls some of the details from the most recent State for each Object.
On the page that is displaying this information, a user can enter some comments, which creates a new State. After creating the new State, I immediately pull the Object from ObjectDisplay and send it back to be dropped into a partial view and replace the Object in the grid on the page.
// Add new State.
db.States.Add(new State()
{
ObjectId = objectId,
Comments = comments,
UserName = username
});
// Save the changes (executes all of the above).
db.SaveChanges();
// Return the new Object information.
return db.Objects.Single(c => c.ObjectId == objectId);
According to my db trace, the Single call occurs about 70 ms after the SaveChanges call, and it occurs on the same SPID.
Now for the issue: The database defaults the value of RecordDate in State to GETUTCDATE() - I don't provide the date myself. What I'm seeing is that the Object returned has the State's RecordDate of the old State and the Comments of the new State information of the old State. I am seeing that the Object returned has the old State's information. When I refresh the page, all the correct information is there, but the wrong information is returned in the initial call from the database/EF.
So.. what could be wrong? Could the view not be updating quickly enough? Could something be going on with EF? I don't really know where to start looking.
If you've previously loaded the same Object entity in the same DbContext, EF will return the cached instance with the stale values, and ignore the values returned from SQL.
The simplest solution is to reload the entity before returning it:
var result = db.Objects.Single(c => c.ObjectId == objectId);
db.Entry(result).Reload();
return result;
This is indeed odd. In SQL Server views are not persisted by default and therefore show changes in the underlying data right away. You can create a clustered index on a view with effectively persists the query, but in that case the data is updated synchronously, so you should see the change right away.
If you are working with snapshot isolation level your changes might not be visible to other SPIDs right away, but as you are on the same SPID and do not use snapshot isolation, this cant be the culprit either.
The only thing left at this point is the application layer. Are you actually using the result of the Single call higher up in the call stack or does that get lost somewhere. I assume that a refresh of the page uses a different code path, which would explain why it is working there.