Export-DbaCredential - Add IF NOT EXISTS guard to exported SQL scripts

[andreasjordan]

Wraps each CREATE CREDENTIAL statement with an IF NOT EXISTS check against sys.credentials so that exported scripts are idempotent and only create missing credentials during migrations or DR script replays.

Closes #8618

Generated with Claude Code

[andreasjordan]

@claude please read the other Export-Dba* commands and see if this pattern should be applied there as well.

[claude]

Claude finished @andreasjordan's task in 1m 26s —— View job

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Analysis: IF NOT EXISTS Pattern Across Export-Dba* Commands

• Find all Export-Dba* commands
• Analyze each command for CREATE statements that could use IF NOT EXISTS
• Report findings

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Here's the status of each Export-Dba* command that generates executable SQL statements:

Command	Status	Notes
Export-DbaCredential	✅ Added (this PR)	IF NOT EXISTS (SELECT 1 FROM sys.credentials ...)
Export-DbaLogin	✅ Already handled	IF NOT EXISTS (SELECT loginname FROM master.dbo.syslogins ...) (lines 410, 414)
Export-DbaServerRole	✅ Already handled	ScriptingOptionsObject.IncludeIfNotExists = $true (line 230)
Export-DbaUser	✅ Already handled	ScriptingOptionsObject.IncludeIfNotExists = $true (line 250)
Export-DbaSpConfigure	✅ N/A	Generates EXEC sp_configure calls, not CREATE statements
Export-DbaDbRole	⚠️ Gap found	Explicitly sets IncludeIfNotExists = $false (line 261)
Export-DbaLinkedServer	⚠️ Partial gap	Uses SMO Script() which generates EXEC sp_addlinkedserver — no idempotency guard
Export-DbaSysDbUserObject	ℹ️ Minor	Delegates to Export-DbaScript; IncludeIfNotExists not set in scripting options

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Key Finding: Export-DbaDbRole

This is the clearest gap. While Export-DbaServerRole and Export-DbaUser both set IncludeIfNotExists = $true, Export-DbaDbRole explicitly sets it to $false at public/Export-DbaDbRole.ps1:261:

$ScriptingOptionsObject.IncludeIfNotExists = $false

Changing this to $true would make Export-DbaDbRole consistent with its sibling commands and make its generated CREATE ROLE statements idempotent.

Fix this →

Secondary Finding: Export-DbaLinkedServer

This command uses SMO's Script() method which generates EXEC sp_addlinkedserver / EXEC sp_addlinkedsrvlogin stored procedure calls rather than CREATE statements. There's no idempotency guard — if a linked server already exists, the script will fail. However, fixing this would require a custom approach (checking sys.servers) similar to what was done for credentials, rather than just flipping an SMO flag. That's a more involved change worth its own issue/PR.