How to prevent duplicate child records for the same parent record?

Record Triggered Flow- Summer’20 Salesforce Release Feature

Duplicate Message

Requirement:
I have a business use case where I need to restrict users from entering duplicate child records for the same parent record.

Logic:

• I decided to create one unique text field on the child object and then update it with a unique key value.
• As the field marked as unique if a duplicate record comes with the same key then the system will throw an error message.

Solution Spectrum:

I had various options on hand to achieve this but I found the record triggered flow is the best option.

• Option 1: Formula Field + Using Duplicate and matching rule
• Option 2: Text Field + Workflow Field Update + Duplicate and matching rule
• Option 3: Text field + Process Builder
• Option 4: Before Event Apex Trigger
• Option 5: Before Event, Record Triggered Flow (Summer’20 Release)

Option 1: Formula Field + Using Duplicate and matching rule

Steps:

• I created a formula field on the child object to populate (Parent.Id+CurrentRecord.State) Because I wanted unique records by State.
• Then I tried to use this field in the Matching rule to find duplicates, but it's not available there because of the formula field.

Outcome:

• This Solution didn’t work.

Option 2: Text Field + Workflow Field Update + Duplicate and matching rule

Steps:

• Create a Text field instead of a formula field.
• Update field with unique key value using a workflow field update on the child object.
• Create duplicate and matching rules to show an error message.

Pros:

• Easy to configure
• User-friendly error message on duplication

Cons:

• Performance issue — Rules on child records, will execute for all records under the parent.
• Workflows are executed very late in the execution context
• Same object update is there hence recursion must be handled.
• Because of this update if there are any other workflows or process builders or triggers are there on the same object then those will be executed.

Outcome:

• Works but not recommended, due to poor performance.

Option 3: Text field (Mark it as Unique) + Process Builder

Steps:

• Create a Text field marked as unique.
• Update field with unique key value using a Process builder action field update on the child object.

Pros:

• Easy to configure
• The unique field will handle to display the error

Cons:

• Performance issue — Process Builder
• Same object update is there hence recursion must be handled.
• Because of this update if there are any other workflows or process builders or triggers are there on the same object then those will be executed.

Outcome:

• Works but not recommended, due to poor performance.

Option 4: Before Event Apex Trigger

Steps:

• Write before insert/update event trigger
• throw error from trigger using .addError() standard method.

Pros:

• Easy to build
• Before the event trigger, it is, hence no need to make any DML
• No need to worry about recursion

Cons:

• Test class and Code coverage is required

Outcome:

• This solution works but a better solution is available :)

Option 5: Before Event, Record Triggered Flow (Summer’20 Release)

Steps:

• Create a Text field mark it as Unique.
• Update field with unique key value using a flow (Before Save Record Triggered)
• The system will throw an error preventing duplication.

Pros:

• Easy to configure
• Faster performance
• No need to worry about recursion
• Doesn’t fire any other workflow, process builder or triggers

Cons:

• Not really if you are comfortable building a flow.

Outcome:

• Works very well.

Thank you for reading my post, please share your thoughts and comments.
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