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Use case
Prevent issue creation when there is already another issue in the same project with the same value in a certain field.
In this use case let's suppose that we have a text custom field called Invoice, and we want to avoid this field's value to be repeated among issues of the same issue type in the same project.
This use case is based on the Prevent issue creation with the same field value with Validation based on JQL query.
Configuration
Add the Logical validator to the "Create issue" transition of the desired workflow.
Expression*
Add the following expression:
count(issuesFromJQL("project = '" + %{00018} + "' AND issuetype = '" + %{00014} + "' AND Invoice = '" + %{10200} + "'")) = 0
Screenshots
Related use cases
STAFF PICKUse case JWT feature Workflow function Parser functions Label Assignee may only have a restricted number of assigned issues 
Prevent creation of issues with a duplicate summary Prevent issue creation with the same field value
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