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pagination.md

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title Pagination
parent Examples
nav_order 2
permalink /examples/pagination/
description Plain refinements with aliases for page numbers, page sizes, and computed offsets.

Pagination

This example uses plain refinements and refinement aliases to describe common pagination rules. The aliases keep the contracts readable while still relating results to the input values.

import liquidjava.specification.*;

@RefinementAlias("Page(int p) { p >= 1 }")
@RefinementAlias("PageSize(int s) { 1 <= s && s <= 100 }")
@RefinementAlias("PageCount(int p) { p >= 0 }")
@RefinementAlias("ItemCount(int n) { n >= 0 }")
public class Pagination {
    @Refinement("ItemCount(_) && _ == (page - 1) * size")
    public static int offset(
        @Refinement("Page(_)") int page,
        @Refinement("PageSize(_)") int size
    ) {
        return (page - 1) * size;
    }

    @Refinement("Page(_) && _ == page + 1")
    public static int nextPage(@Refinement("Page(_)") int page) {
        return page + 1;
    }

    @Refinement("PageCount(_) && _ == (items + size - 1) / size")
    public static int totalPages(
        @Refinement("ItemCount(_)") int items,
        @Refinement("PageSize(_)") int size
    ) {
        return (items + size - 1) / size;
    }
}
int size = 20;
int page = 3;
int offset = Pagination.offset(page, size);
int next = Pagination.nextPage(page);
int total = Pagination.totalPages(50, size);
Pagination.offset(0, 20); // Refinement Error
Pagination.totalPages(50, 200); // Refinement Error

The aliases capture the key domain concepts for pagination:

  • Page says page numbers start at 1
  • PageSize constrains the accepted page size range
  • PageCount prevents negative page counts
  • ItemCount prevents negative item counts