unique

Defines a UNIQUE UniqueConstraint on one or more KQLiteTable columns.

A UNIQUE constraint ensures that all values in a column or a combination of columns are unique. This constraint can be applied to a single column or multiple columns (a composite unique key). While similar to a PRIMARY KEY, a table can have multiple UNIQUE constraints, and they can permit NULL values (though how multiple NULLs are handled can vary between database systems; SQLite allows multiple NULLs).

Use this function within the constraints block of a KQLiteTable definition. You can specify the conflict resolution strategy by chaining UniqueConstraint.onConflict on the result.

Example (Single Column Unique Constraint)

object Users : KQLiteTable("users") {
    val userId = longColumn("UserId").primaryKey()
    val email = textColumn("Email").notNull()

    override val constraints: (ConstraintBuilder.() -> Unit)? = {
        constraint("unique_email").unique(email).onConflict(Action.REPLACE)
    }
}

Example (Composite Unique Constraint)

object CourseRegistrations : KQLiteTable("course_registrations") {
    val studentId = longColumn("StudentId")
    val courseId = longColumn("CourseId")

    override val constraints: (ConstraintBuilder.() -> Unit)? = {
        // A student can only register for a specific course once.
        constraint("unique_student_course").unique(studentId, courseId)
    }
}

Parameters

See also