Mixer/.claude/skills/ash-framework/references/exist_expressions.md

Exists Expressions

Use exists/2 to check for the existence of records, either through relationships or unrelated resources:

Related Exists

# Check if user has any admin roles
Ash.Query.filter(User, exists(roles, name == "admin"))

# Check if post has comments with high scores
Ash.Query.filter(Post, exists(comments, score > 50))

Unrelated Exists

# Check if any profile exists with the same name
Ash.Query.filter(User, exists(Profile, name == parent(name)))

# Check if user has any reports
Ash.Query.filter(User, exists(Report, author_name == parent(name)))

# Complex existence checks
Ash.Query.filter(User, 
  active == true and 
  exists(Profile, active == true and name == parent(name))
)

Unrelated exists expressions automatically apply authorization using the target resource's primary read action. Use parent/1 to reference fields from the source resource.