public static <D> SimpleExpression<D> as(Expression<D> source, Path<D> alias) {
        if (source == null) {
            return as(Expressions.<D>nullExpression(), alias);
        } else {
            return operation(alias.getType(), Ops.ALIAS, source, alias);
        }
    }
Create a {@code source as alias} expression

@param source source
@param alias alias
@param <D>
@return source as alias
querydsl-core/src/main/java/com/querydsl/core/types/dsl/Expressions.java