View source for Training:Bootcamp:Chapter 15

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This is '''Chapter 15'''. If you want to go back to the beginning, [[The 1000 steps program to MDriven Chapter 1|you can find it here: Chapter 1.]] Or link to [[The_1000_steps_program_to_MDriven_Chapter_14|Chapter 14.]]

== Video 15: Importing SysAsyncTicket ==
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 <span data-video="04ssHZbuZyk" data-start="00" tabindex="0"> <strong> Steps 462 - 492 </strong> </span>
    <span class="navigation-item" data-video="04ssHZbuZyk" data-start="00" tabindex="0"> Introduction </span>
    <span class="navigation-item" data-video="04ssHZbuZyk" data-start="29" tabindex="0"> Create a new method </span>
    <span class="navigation-item" data-video="04ssHZbuZyk" data-start="75" tabindex="0"> Write logic for a new Registration number </span>
    <span class="navigation-item" data-video="04ssHZbuZyk" data-start="1314" tabindex="0"> Upload the model to MdrivenServer </span>
    <span class="navigation-item" data-video="04ssHZbuZyk" data-start="1354" tabindex="0"> Verify the method </span>
    <span class="navigation-item" data-video="04ssHZbuZyk" data-start="2075" tabindex="0"> Merge SysAsyncTicket </span>
    <span class="navigation-item" data-video="04ssHZbuZyk" data-start="2465" tabindex="0"> Upload the model and run the app </span>
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== Chapter 15: Part 1 - Assign a new registration number ==
'''In this chapter, we create some methods to assign a new registration number and import the SysAsyncTicket model pattern that is recognised by the MDrivenServer.'''

* '''The SysAsyncTicket pattern is a major facilitator when it comes to things that must be serialized, like assigning a new number from a common store. If the assignment is not serialized, we will always run the risk of giving the same number to 2 different cars (due to 2 users, the system does the assignment roughly at the same time).'''

462. Create a new method on the class '''Car''' called <code>GetNewRegistrationNumber():String</code>

463. We will write logic to create a new Registration number in the format '''ABC123'''. We want the logic to count upwards without giving the same number twice. To enable that, we need to remember how the last number was generated to increase it by 1 the next time. We will place this "memory" on SysSingleton in four attributes.

464. Create new attributes on SysSingleton:

* RegNumberLetter1Current:Integer?
* RegNumberLetter2Current:Integer?
* RegNumberLetter3Current:Integer?
* RegNumberNumberPartCurrent: Integer?
 
465. Now, '''watch''' the video until '''20:00'''. Follow along with the video and write the same code or find it [[1000 Steps Program: Chapter 15 - Code Snippets|here]]. You should be able to understand why it works.

466. Follow the discussion on '''semicolons''' in the video.

* The '''semicolon''' (''';''') is used to separate expressions.
* In OCL (in all functional languages), we must return exactly 1 result (the result can be 1 list - that is, still 1 result).
* This means that when we want to create a method that does multiple things, we need a way to stack multiple expressions together and ignore all the results but the last result. That is what the semicolon does for us. So '''<code>expr1;expr2</code>''' will return a result of '''<code>expr2, expr1;expr2;expr3</code>'''. A result of '''<code>expr3</code>''' and '''<code>expr1;expr2;expr3;</code>''' is actually wrong - because we ''cannot'' end on a semicolon.

467. Assign default values and default DB-values “'''=65'''”.

* RegNumberLetter1Current=65
* RegNumberLetter2Current=65
* RegNumberLetter3Current=65
* Set the InitialValue for all three to “65” as well.

468. Assign InitialValue to the NumberPart: '''RegNumberNumberPartCurrent=1'''.

469. Ensure your MDrivenServer is running. Upload the model to the MdrivenServer. We expect to see that it evolves the database with the new attributes we added.

470. Press the play button and go into the debugger with persistence set to MDrivenServer.

471. Open a debugger search window for Cars, search, and drag the first car onto an Expressions green dot in the debugger (we do this to give "self" the value of the car in the debugger expression).

472. Switch the debugger expression to Action and execute <code>self.GetNewRegistrationNumber</code> to see what happens.

473. Discover that the method does not behave as we expect. Start the expression with the "'''Step'''" function in the debugger.

474. Press '''Start''' to step through the expression. Use the '''Step into''' to get into the code of the method. Familiarise yourself with the OCL stepper - it will be used frequently to discover the true logic of what you have.

475. '''Watch''' the video up to '''26 minutes''' to see that you understand the issue - then correct the method.

476. Once corrected, upload the model again. It is important that the Server is given the latest model, or it will continue to have errors from the old model.

477. If you still have the debugger up, remember to press "'''Re-Read Model'''" - this is important for the same reason as the above (Step 476).

478. Use a search window to find a car and drag in a self on the green dot to the expression - then execute (F5) the <code>self.GetNewRegistrationNumber</code> again.

479. Verify that it now works better. Press F5 to execute and hold it down to loop execute. See what happens when the first letter reaches Z and continue to watch the second letter reach Z. Cancel the changes when you are done.

== Chapter 15: Part 2 - The SysAsyncTicket (Starts at [https://youtu.be/04ssHZbuZyk?si=Po9L9lrwddjVTZ7K&t=1700 about 28 minutes into the Video]) ==
480. In the State '''BrandNew''' for '''Car''' (in the State Diagram for Car), add an Entry action that assigns the '''RegistrationNumber''' property, a value from our method '''GetNewRegistrationNumber'''.

·      Write <code>self.RegistrationNumber:=self.GetNewRegistrationNumber</code>

481. Save and upload the model to MDrivenServer. Use a browser to check your application. Create a new Car and see that it gets a new Registration Number.

482. Now open another browser as another Chrome user ('''b@b.se'''), or in incognito mode, and log in again. You now have two different server contexts. Place the browsers next to each other on the screen, both showing the Car Seeker.

* '''Note''': the '''b''' user does not have the right to create a New Car. Log in as the '''a''' user ('''a@a.se''') instead.
* Press '''New Car''' in both windows. Notice that they are given the same number - this is not right.

483. Think about this problem for a minute.

* It is a common problem in all information systems.
* We want the system to behave asynchronously in 99.9% of the cases so that 1 user is not blocked by another user doing lengthy operations.
* In cases like this, we will want a serialization of the number generation and assignment to ensure that a conflict can never happen - not even in theory.

484. Now go to the Wiki and find the merge model for [[Documentation:AsyncTicket|SysAsyncTicket]]. Download and merge it into your model.

485. Ensure that your current packages have the SysSuperClass as the default superclass (meaning that all classes without an explicit superclass will inherit from SysSuperClass). This is good - we get access to the method '''DoAsync''' that the pattern added for us.

486. Change the Entry action of '''Car''' <u>BrandNew</u> state to <code>self.ActuallyAssignNewNumber</code> and move the old code into this new method instead (you need to create the method on Car).   

487. Again, change the Entry action to use <code>self.DoAsync('ActuallyAssignNewNumber')</code> instead of calling it directly. This will move the execution to the Server, and the Server will serialize jobs with the same signature. This is the effect that we are after.

488. Upload the model and run the app again. Create a new car and save. Wait for the new registration number to come back from the Server.

489. Have the two different apps next to each other again. Verify that you cannot get the same number on two new cars no matter how hard you try.

490. Familiarise yourself with the MDrivenServer ('''<nowiki>http://localhost:5000</nowiki>''') by logging into its admin UI '''a''', password '''123456''',  (or the port you have in the Cloud-connect dialog).

* Go to <u>Running</u>, then <u>PeriodicActions</u>. Observe the actions that check for SysAsyncTicket and delete old SysAsyncTickets.
* Go to <u>Running</u>, then <u>Data in A0</u>. Click on SysAsyncTicket. Press “Search”. Observe the data for '''Car.ActuallyAssignNewNumber'''. There are no reported issues.
* Go to <u>Running</u>, then <u>WorkInfo</u>. View the different events tracked in the Server.

491. Head back to the model and check the "Changed by - Cross Reference" on the '''RegistrationNumber''' attribute. We want to limit the manual ability to set this value by setting a read-only expression that's true everywhere this is shown in the UI (switching to '''IsStatic''' would also work).

* Click on “ViewModelColumn ProperCarView.RegistrationNumber R/W”
* Select '''RegistrationNumber''' and in the Readonly Expression box, write: '''<code>true</code>'''
* Go back to the model and check the "Changed by - Cross Reference" on the '''RegistrationNumber''' attribute. You’ll find the value shows also on '''TheTemplateForCarTransferOwnershipDocumentReport'''. Click on it.
* In the ViewModel window, press on '''TheTemplateForCarTransferOwnershipDocumentReport''' and set the Readonly Expression to '''true''' to avoid further confusion.

492. Find and select the '''RegistrationNumber''' attribute in '''Car'''. Click on the <u>Tagged Values</u> dialog. We want to give this the tag value of <code>Realtime=true</code>. (Read about Realtime [[Documentation:SignalR and Realtime|here]].)

* In the Tagged Values dialog, press “Refresh From Wiki”. Click on “<Create Empty TV>” and select '''Realtime'''. Close the dialog.
* Save and upload the model.
* Test to create a new car and notice that the '''RegistrationNumber''' comes back faster than before.

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'''Next Chapter''' 

[[The_1000_steps_program_to_MDriven_Chapter_16]]
[[Category:1000 Steps Program]]