Could somebody please give their input into the following scenario:
I have an Administrator class and a Technician class (both extending a User class but that is besides the point). I also have a RepairJob class which represents an item through its varying stages of being repaired {received|being repaired|waiting for part, etc.}.
Only administrator users will be able to add a new repair job to the system and will also be able to view the status of all the repair jobs currently ongoing.
Technicians will need to be able to accept repair jobs from a view of the list of any repair jobs which have not yet been accepted by other technicians. Technician uses will also have to be able to update the status of a repair job accepted by themselves until it's ready to be returned to the Customer (another class).
An administrator will be able to accept any repair job in the system, even those already accepted by a Technician at which point they will no longer be able to update the status of the repair job. (To take account of employees being off work)
My Question
Could somebody give me an insight into how you would collect together the RepairJob instances. I had thought at first that since the administrator user would be adding these instances that it would be a good idea to model the collection inside the Administrator class however the Technician class will also have to be able to access a limited collection of repair jobs. I had also though of creating a RepairJobs class which had the list and was available to either class but I'm not sure if this would be a good design.
I think it ought to be separate from Admin and Tech classes. RepairJob is for a single task; what you're describing sounds like a RepairJobManager that maintains a collection of RepairJobs and tracks their status. It executes your rules according to the Role of the particular User that interacts with it.
package model;
public class RepairJobManager
{
private Map<String, RepairJob> jobs;
public void add(RepairJob job, Role role)
{
// Only allow Admin to do certain things.
}
public void update(RepairJob job, Status status, Role role)
{
// Only allow Admin to do certain things.
}
}
My DDD view: You need a RepairJobRepository which holds a collection of RepairJobs. Also you need a RepairService with operations like
- create(RepairJob jobSpec) (add the created job to the repository)
- assign(RepairJob job, Role role)
RepairJob need a method like updateStatus(Status newStatus, Person p)
You need to get p's role to validate if he could update the status.
Related
i was reading the blogs for "What about the code? Why does the code need to change when it has to run on multiple machines?".
And i came across one line which i am not getting it, can anyone please help me to understand it with simple or any example.
"There should be no static instances in the class. Static instances hold application data and when a particular server goes down, all the static data/state is lost. The app is left in an inconsistent state."
Assuming: Stating instance is an instance which can be at most once per process or context - e.g. in java there is at most one copy of a static class, with all data (or state) that the class contains.
So it is very simple memory model for a static class in a single node/jvm/process. Since there is a single copy of data, it is quite straightforward to reason about it. For example, you one may update the data and every next reader will see the updated information. This is a bit more complicated for multithreaded programs, but is still straightforward comparing to distributed systems.
Clearly in a distributed system, every node may have at most one static class with state. Which means if a system contains several nodes - a distributed system - then there are several copies of data.
Having several copies is a problem. It is hard to reason about such system - every node may have some unique data and data may differ on different node. It is very hard to reason about such data: how it is synced? Availability vs consistency?
For example, take a simple counter. In a single node system, a static instance may keep the score. If one writer increased the counter, the next reader will see the increased value (assuming multithreaded part is implemented correctly, which is not that complicated).
Same counter is a distributed system is much more complicated. A writer may write to one node, but a reader may read from another.
Basically, having state on nodes is a hard problem to solve. This is the primary reason to use some distributed storage layer e.g. Hbase, Cassandra, AWS DynamoDB. All these storage systems have predictable behaviour which helps to reason about correctness of programs.
For example, there are just two servers which accepts payments from clients.
Then somebody decided to create static class to be friendly with mutli threading:
public static class Payment
{
public static decimal Amount;
public static bool IsMoneyReceived;
public static string UserName;
}
Then some client, let's call him John, decided to buy something in shop. John sent money and static class has data about this purchase. Some service is going to write data into database from
Payment class, however, electicity was turned off. Load balancer knows that the server is not responding and redirects John requests to another server which knows nothing about data in
Payment class.
I am working on a .NET Core Web API which needs to interact using EF Core 5.0.2 with an Azure SQL database.
I have different repository methods where I am interacting with DbContext to add/edit/delete records for different DbSet.
For example:
UserRepository.AddUser(userdata);
Implementation of AddUser is like this,
ourDbContext.UserTable.AddAsync(userdata);
So in user service method, am calling different repository method sequentially and none of those methods call ourDbContext.SaveChangesAsync() individually. A single call to SaveChanges is present after all the repository methods calls which is acting like a unit of work pattern for all the calls as single transaction.
Example:
UserRepository.AddUser(userdata);
ActivityRepository.AddActivity("New User got added");
ourDbContext.SaveChangesAsync();
So my question is: if any saving changes to any of the tables/entities fails, will the previous successful tables change will be rolled back?
For example, suppose this operation
UserRepository.AddUser(userdata);
was successful and the new user record was added to the User table.
But this was not successful:
ActivityRepository.AddActivity("New User got added");
So no activity record was added to the Activity table.
Will SaveChangesAsync() be able to handle this situation automatically and will roll back User table new changes as well?
If not are we supposed to wrap the above codes with transaction scope? Or what is the recommended way to do it.
Briefly how DbContext's Change Tracker works:
You load entities: ChangeTracker remembers current values of all loaded entities (except you use AsNoTracking())
You have modified loaded entities, delete, add new.
You call SaveChanges: ChangeTracker starts searching which objects are changed since last load by comparing with previous values.
DML SQL is generated and everything saved in one SQL statement or in several statements in Transaction.
So, if you have one DbContext for each repository, you do not need to worry about rollbacking, just do not call SaveChanges(). For sure for restart process, you have to recreate DbContext because it contains not needed state.
I have a dashboard with a list of items and a finite number of users. I want to show "an item is being edited" near said item to avoid simultaneous edits and overwrites of data.
This seems to me like updating a flag in the database and relatively simple signalr implementation with the javascript simply adding/removing a css class.
I have seen this:
Prevent multiple people from editing the same form
which describes a method with posting every X minutes and clearing the flag from the database when there are no more update messages from the user.
The issue is:
I was wondering if there was a signalr method (like disconnect; i know it exists but I don't know if it fits this scenario) to do that elegantly rather than running a timer function. If so, is it possible for the server to miss the event and permanently leave the flagged as "editing" when it is not?
you could implement a hub for this, here is a example:
public class ItemAccessHub : Hub
{
public override Task OnConnectedAsync()
{
// your logic to lock the object, set a state in the db
return base.OnConnectedAsync();
}
public override Task OnDisconnectedAsync(Exception exception)
{
// your logic to unlock the object
return base.OnDisconnectedAsync(exception);
}
}
to get information from the query you can access the HttpContext:
Context.GetHttpContext().Request.Query.TryGetValue("item-id", out var itemId)
so you could start a connection when the user is accessing the form and send the id of the item in the query:
/hub/itemAccess?item-id=ITEM_ID
and when the user closes the form then disconnect the connection.
with this method the item is also unlocked when the user loses his network connection.
the on disconnect method is allays invoked when a client disconnects, so you can do your clean up in this method.
in this hub you can than also implement the update function
i hope this is what you are looking for
Introduction
I'm currently building an access control system in my DataMapper ORM installation (with CodeIgniter 2.*). I have the initial injection of the User's rights (Root/Anonymous layers too) working perfectly. When a User logs in the DataMapper calls that are done in the system will automatically be marked with the Userrights the User has.
So until this point it works perfectly, but now I'm a bit in a bind. The problem is that I need some way to catch and filter each method-call on the Object that is instantiated.
I have two special calls so I can disable the Userrights-checks too. This is particularly handy at the exact moment I want to login a User and need to do initial checks;
DataMapper::disable_userrights();
$this->_user = new User($this->session->userdata('_user_id'));
$this->_userrights = ($this->_user ? $this->_user->userrights(TRUE) : NULL);
DataMapper::enable_userrights();
The above makes sure I can do the initial User (and it's Userrights) injection. Inside the DataMapper library I use the $CI =& get_instance(); to access the _ globals I use. The general rule in this installment I'm building is that $this->_ is reserved for a "globals" system that always gets loaded (or can sometimes be NULL/FALSE) so I can easily access information that's almost always required on each page/call.
Details
Ok, so image the above my logged-in User has the Userrights: Create/Read/Update on the User Entity. So now if I call a simple:
$test = new User();
$test->get_where('name', 'Allendar');
The $_rights Array inside the DataMapper instance will know that the current logged-in User is allowed to perform certain tasks on "this" instance;
protected $_rights = array(
'Create' => TRUE,
'Read' => TRUE,
'Update' => TRUE,
'Delete' => FALSE,
);
The issue
Now comes my problem. I want to control these Userrights by validating them over each action that is performed. I have the following ideas;
Super redundant; make a global validation method that is executed at the start of each other method in the DataMapper Class.
Problem 1: I have to spam the whole DataMapper Class with the same calls
Problem 2: I have no control over DataMapper extension methods
Problem 3: How to detect relational includes? They should be validated too
Low level binding on certain Core DataMapper calls where I can clearly detect what kind of action is executed on the database (C/R/U/D).
So I'm aiming for Option 2 (and 1.) Problem 2), as it will also solve 1.) Problem 2.
The problem is that DataMapper is so massive and it's pretty complex to discern what actually happens when on it's deepest calling level. Furthermore it looks like all methods are very scattered and hardly ever use each other ($this->get() is often not used to do an eventual call to get a dataset).
So my goal is:
User (logged-in, Anonymous, Root) makes a DataMapper istance
$user_test = new User;
User wants to get $user-test (Read)
$user_test->get(1);
DataMapper will validate the actual call that is done at the database
IF it is only SELECT; OK
IF something else than SELECT (or JOINs to other Model that the User doesn't have access to that/those Models, it will fail with a clear error message)
IF JOINed Models also validate; OK
Return the actual instance;
IF OK: continue DataMapper's normal workflow
IF not OK: inform the User and return the normal empty DataMapper instance of that Model
Furthermore, for this system I think I will need to add some customization for the raw_sql (etc.) SQL calls so that I have to inject the rights manually related to that SQL statement or only allow the Root User to do those things.
Recap
I'm curious if someone ever attempted something like this in DataMapper or has some hints how I can use/intercept those lowest level calls in DataMapper.
If I can get some clearance on the deepest level of DataMapper's actual final query-call I can probably get a long way myself too.
I would like to suggest not to do this in Datamapper itself (mainly due to the complexity of the code, as you have already noticed yourself).
Instead, use a base model, and have that extend Datamapper. Then add the code to the base model required for your ACL checks, and then overload every Datamapper method that needs an ACL check. Have it call your ACL, deal with an access denied, and if access is granted, simply return the result of parent::method();.
Instead of extending Datamapper, your application models should then extend this base model, so they will inherit the ACL features.
private void Subscribe()
{
EventSystem.Subscribe<User, LoadEventArgs>(GetInfo, EventPhases.Initiated);
}
public void GetInfo(User user, LoadEventArgs args, EventPhases phase)
{
TcmUri id = user.Id;
string name = user.Title;
Console.WriteLine(id.ToString());
Console.WriteLine(name);
}
I wrote above code and add the assembly in config file in Tridion server but no console window is coming on login of a user
The event you were initially subscribing to is the processed phase of any identifiable object with any of its actions, that will trigger basically on every transaction happening in the SDL Tridion CMS, so it won't give you any indication of when a user logs in (it's basically everything which happens all the time).
Probably one of the first things which is happening after a user logs in, is that its user info and application data is read. So what you should try is something along the lines of:
private void Subscribe()
{
EventSystem.Subscribe<User, LoadEventArgs>(GetInfo, EventPhases.Initiated);
}
public void GetInfo(User user, LoadEventArgs args, EventPhases phase)
{
TcmUri id = user.Id;
string name = user.Title;
}
But do keep in mind that this will also be triggered by other actions, things like viewing history, checking publish transactions and possibly a lot more. I don't know how you can distinguish this action to be part of a user login, since there isn't an event triggered specifically for that.
You might want to check out if you can find anything specific for a login in the LoadEventArgs for instance in its ContextVariables, EventStack, FormerLoadState or LoadFlags.
Edit:
Please note that the Event System is running inside the SDL Tridion core, so you won't ever see a console window popup from anywhere. If you want to log information, you can include the following using statement:
using Tridion.Logging;
After adding a reference to the Tridion.Logging.dll which you can find in your ..\Tridion\bin\client directory. Then you can use the following logging statement in your code:
Logger.Write("message", "name", LoggingCategory.General, TraceEventType.Information);
Which you will find back in your Tridion Event log (provided you have set the logging level to show information messages too).
But probably the best option here is to just debug your event system, so you can directly inspect your object when the event is triggered. Here you can find a nice blog article about how to setup debugging of your event system.
If you want to get the TCM URI of the current user, you can do so in a number of ways.
I would recommend one of these:
Using the Core Service, call GetCurrentUser and read the Id property.
Using TOM.NET, read the User.Id property of the current Session.
It looks like you want #2 in this case as your code is in the event system.