public NumberExpression<Integer> dayOfWeek() {
        if (dayOfWeek == null) {
            dayOfWeek = Expressions.numberOperation(Integer.class, Ops.DateTimeOps.DAY_OF_WEEK, mixin);
        }
        return dayOfWeek;
    }
Create a day of week expression (range 1-7 / SUN-SAT)
<p>NOT supported in JDOQL and not in Derby</p>

@return day of week
querydsl-core/src/main/java/com/querydsl/core/types/dsl/DateExpression.java