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content/docs/BestPractices/SubscriberCodeunits/index.md
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content/docs/BestPractices/SubscriberCodeunits/index.md
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---
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title: "Subscriber Codeunits"
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tags: ["Performance"]
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categories: ["Best Practice"]
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---
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_Created by waldo, Described by waldo_
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## Description
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In general, subscribers have to be put in codeunits. There are a few performance considerations that you should keep in the back of your minds, when designing such a codeunit.
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- Keep the codeunit as small as possible
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- Work with a single instance codeunit
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- only subscribe when necessary
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- Avoid generic OnInsert/OnModify/OnDelete
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Let's discuss all points
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## Keep the codeunit as small as possible
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Every time a subscriber gets called, a new instance of the codeunit is being loaded in memory, which takes memory and processing power. The smaller the codeunit, the less memory, and the faster it is.
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Therefore, it's suggested to split the subscribers by functionality and avoid putting business logic in the actual codeunit. Tip: put all business logic in an "[Method Codeunit](https://alguidelines.dev/bcpatterns/generic-method-pattern/)".
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Examples:
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- if you app does things on Sales and Purchase, create a Sales-subs codeunit, and a Purchase-subs.
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- if you have multiple functionalities in your app (let's call'm modules), create a subs-codeunit per module, and only add the subscribers in there that are necessary for that module.
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### Bad code
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```AL
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codeunit 2037325 "Setup Subs"
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{
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SingleInstance = true;
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[EventSubscriber(ObjectType::Codeunit, Codeunit::"Manual Setup", 'OnRegisterManualSetup', '', false, false)]
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local procedure OnRegisterManualSetup(sender: Codeunit "Manual Setup")
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var
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AppId: ModuleInfo;
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NameListLbl: Label 'Linked Texts Framework - List', Locked = true;
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DescriptionListLbl: Label 'Edit linked texts', Locked = true;
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KeyWordListLbl: Label 'LT,Distri,Technical,Functional,Reports', Locked = true;
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NameReportLbl: Label 'Linked Texts Framework - Reports', Locked = true;
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DescriptionReportLbl: Label 'View linked texts reports', Locked = true;
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KeyWordReportLbl: Label 'LT,Distri,Technical,Functional,Reports', Locked = true;
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begin
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navapp.GetCurrentModuleInfo(AppId);
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Sender.Insert(NameListLbl, DescriptionListLbl, KeyWordListLbl, page::"LTE Linked Text List", AppId.Id(), "Manual Setup Category"::General);
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Sender.Insert(NameReportLbl, DescriptionReportLbl, KeyWordReportLbl, page::"LTE Linked Texts Reports", AppId.Id(), "Manual Setup Category"::General);
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end;
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[EventSubscriber(ObjectType::Codeunit, codeunit::"Manual Setup", 'OnRegisterManualSetup', '', false, false)]
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local procedure OnRegisterManualSetup(sender: Codeunit "Manual Setup")
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var
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AppId: ModuleInfo;
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NameLayoutLbl: Label 'Report Helper - Layout', Locked = true;
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DescriptionLayoutLbl: Label 'Set up or update report layout list', Locked = true;
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KeyWordLayoutLbl: Label 'RH,Distri,Technical,Functional,Reports,Layout', Locked = true;
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NameCaptionsLbl: Label 'Report Helper - Captions', Locked = true;
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DescriptionCaptionsLbl: Label 'Set up or update captions list', Locked = true;
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KeyWordCaptionsLbl: Label 'RH,Distri,Technical,Functional,Reports,Captions', Locked = true;
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NameFunctionsLbl: Label 'Report Helper - Functions', Locked = true;
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DescriptionFunctionsLbl: Label 'Set up or disable functions', Locked = true;
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KeyWordFunctionsLbl: Label 'RH,Distri,Technical,Functional,Reports,Functions', Locked = true;
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NameDFCLbl: Label 'Report Helper - Default Footer', Locked = true;
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DescriptionDFCLbl: Label 'Set up or update default footer', Locked = true;
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KeyWordDFCLbl: Label 'RH,Distri,Technical,Functional,Reports,Default,Footer', Locked = true;
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begin
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navapp.GetCurrentModuleInfo(AppId);
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Sender.Insert(NameLayoutLbl, DescriptionLayoutLbl, KeyWordLayoutLbl, page::"RHE Report Layout List", AppId.Id(), "Manual Setup Category"::General);
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Sender.Insert(NameCaptionsLbl, DescriptionCaptionsLbl, KeyWordCaptionsLbl, page::"RHE Captions", AppId.Id(), "Manual Setup Category"::General);
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Sender.Insert(NameFunctionsLbl, DescriptionFunctionsLbl, KeyWordFunctionsLbl, page::"RHE Functions", AppId.Id(), "Manual Setup Category"::General);
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Sender.Insert(NameDFCLbl, DescriptionDFCLbl, KeyWordDFCLbl, page::"RHE Default Footer Card", AppId.Id(), "Manual Setup Category"::General);
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end;
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}
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```
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### Good code
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Split into 2 codeunits, and move the business logic out.
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```AL
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codeunit 2037325 "LTE Setup Subs"
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{
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SingleInstance = true;
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[EventSubscriber(ObjectType::Codeunit, Codeunit::"Manual Setup", 'OnRegisterManualSetup', '', false, false)]
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local procedure OnRegisterManualSetup(sender: Codeunit "Manual Setup")
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var
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RegisterLTEManualSetup: codeunit "Register LTE Manual Setup";
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begin
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RegisterLTEManualSetup.RegisterLTEManualSetup();
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end;
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}
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codeunit 2037324 "RHE Setup Subs"
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{
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SingleInstance = true;
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[EventSubscriber(ObjectType::Codeunit, Codeunit::"Manual Setup", 'OnRegisterManualSetup', '', false, false)]
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local procedure OnRegisterManualSetup(sender: Codeunit "Manual Setup")
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var
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RegisterRHEManualSetup: codeunit "Register RHE Manual Setup";
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begin
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RegisterRHEManualSetup.RegisterRHEManualSetup();
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end;
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}
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```
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## Work with a single instance codeunit
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To avoid the extra "loading of the content" while a subscriber is being executed, use Single Instance codeunit for subscribers. Do take into account, of course, that it would share the state across the entire session.
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### Bad code
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```AL
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codeunit 2037324 "RHE Setup Subs"
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{
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[EventSubscriber(ObjectType::Codeunit, Codeunit::"Manual Setup", 'OnRegisterManualSetup', '', false, false)]
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local procedure OnRegisterManualSetup(sender: Codeunit "Manual Setup")
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var
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RegisterRHEManualSetup: codeunit "Register RHE Manual Setup";
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begin
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RegisterRHEManualSetup.RegisterRHEManualSetup();
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end;
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}
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```
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### Good code
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```AL
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codeunit 2037324 "RHE Setup Subs"
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{
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SingleInstance = true;
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[EventSubscriber(ObjectType::Codeunit, Codeunit::"Manual Setup", 'OnRegisterManualSetup', '', false, false)]
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local procedure OnRegisterManualSetup(sender: Codeunit "Manual Setup")
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var
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RegisterRHEManualSetup: codeunit "Register RHE Manual Setup";
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begin
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RegisterRHEManualSetup.RegisterRHEManualSetup();
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end;
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}
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```
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## only subscribe when necessary
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If possible, only execute the subscriber when really necessary by using Manual Binding.
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### Bad code
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```AL
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//subscriber - code should actually only run when Color=Red.
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[EventSubscriber(ObjectType::Table, Database::"Just Some Table WLD", 'OnAfterValidateEvent', 'Message 2', false, false)]
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local procedure JustDoSomthing(var Rec: Record "Just Some Table WLD"; var xRec: Record "Just Some Table WLD")
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begin
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if Rec.color <> 'RED' then
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exit; //only execute when necessary
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...
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end;
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//business logic
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if JustSomeTable.FindSet() then
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repeat
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JustSomeTable.Validate("Message 2", format(Random(1000)));
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until JustSomeTable.Next() < 1;
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```
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### Good code
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```AL
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if JustSomeTable.FindSet() then
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repeat
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if JustSomeTable.Color = 'RED' then
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BindSubscription(DemoSubs);
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JustSomeTable.Validate("Message 2", format(Random(1000)));
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if JustSomeTable.Color = 'RED' then
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UnbindSubscription(DemoSubs);
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until JustSomeTable.Next() < 1;
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```
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## Avoid OnInsert/OnModify/OnDelete
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The reason for this is, that it breaks the batch-calls:
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- Any "OnInsert" subscriber breaks the bulk inserts, simply because it needs to perform an operation after every record that was inserted
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- Any "OnModify" subscriber slows down the "ModifyAll", simply because it needs to perform an operation after every record that was modified. I fact: 1 SQL call is turned into a loop of SQL calls.
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- Any "OnDelete" subscriber slows down the "DeleteAll", simply because it needs to perform an operation after every record that was deleted. I fact: 1 SQL call is turned into a loop of SQL calls.
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Avoid subscribers to these events.
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## [Discussions](https://github.com/microsoft/alguidelines/discussions/92)
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You can discuss this guidelines [here](https://github.com/microsoft/alguidelines/discussions/92).
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You can find discussions on all "Best Practices" [here](https://github.com/microsoft/alguidelines/discussions/categories/bc-best-practices).
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If you don't find the discussion of this guideline, please feel free to create a new one with the same title as this article.
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## References
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The [Generic Method Pattern](https://alguidelines.dev/bcpatterns/generic-method-pattern/)
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