/**
* @return a set of fetch options for the current limit, offset, and cursors, based on the default
* fetch options. There will always be options even if default.
*/
private FetchOptions fetchOptions() {
FetchOptions opts = FetchOptions.Builder.withDefaults();
if (this.startAt != null) opts = opts.startCursor(this.startAt);
if (this.endAt != null) opts = opts.endCursor(this.endAt);
if (this.limit != 0) opts = opts.limit(this.limit);
if (this.offset != 0) opts = opts.offset(this.offset);
if (this.chunk == null) opts = opts.chunkSize(DEFAULT_CHUNK_SIZE);
else opts = opts.chunkSize(this.chunk);
return opts;
}
/**
* @return a set of fetch options for the current limit and offset, or null if there is no limit
* or offset.
*/
private FetchOptions fetchOptions() {
// The FetchOptions builder interface is really, really awful
if (this.cursor != null) {
FetchOptions opts = FetchOptions.Builder.withCursor(this.cursor);
if (this.limit != 0) opts = opts.limit(this.limit);
if (this.offset != 0) opts = opts.offset(this.offset);
return opts;
} else if (this.limit != 0) {
FetchOptions opts = FetchOptions.Builder.withLimit(this.limit);
if (this.offset != 0) opts = opts.offset(this.offset);
return opts;
} else if (this.offset != 0) {
FetchOptions opts = FetchOptions.Builder.withOffset(this.offset);
return opts;
} else {
return null;
}
}
/**
* Tests pagination of datastore entities. Verifies forward and backward paging returns entities
* in the exact same order, even with duplicate values.
*
* @throws Exception
*/
public void test() throws Exception {
// Initialize some test entities.
final List<Entity> entities = initializeTestData();
// Add the entities to the datastore.
DatastoreServiceFactory.getDatastoreService().put(entities);
// Create a query to get the people, sorted by their initials.
Query q = new Query(KIND);
q.addSort(PROPERTY_NAME, SortDirection.ASCENDING);
// This is to guarantee the order of duplicate initials. This is not
// necessary if you are not concerned with the order of the duplicates.
q.addSort(KEY, SortDirection.ASCENDING);
// Fetch with a page size of 30 people.
final FetchOptions options = FetchOptions.Builder.withDefaults();
options.limit(30);
// Get first page.
final Page page1 = getPage(q, options);
System.out.println("Page 1");
System.out.println(page1);
// Get the next page by setting the cursor to the "next" cursor
// from the current page.
options.startCursor(page1.next);
final Page page2 = getPage(q, options);
System.out.println("Page 2");
System.out.println(page2);
// Make sure the next page starts after the previous page.
assertTrue(page1.last().compareTo(page2.first()) < 0);
// Get the next page by setting the cursor to the "next" cursor
// from the current page.
options.startCursor(page2.next);
final Page page3 = getPage(q, options);
System.out.println("Page 3");
System.out.println(page3);
// Make sure the next page starts after the previous page.
assertTrue(page1.last().compareTo(page2.first()) < 0);
// For paging backward, create the same query in the reverse order.
// Of course, each page will create a new query according to the
// page direction desired.
q = new Query(KIND);
q.addSort(PROPERTY_NAME, SortDirection.DESCENDING);
q.addSort(KEY, SortDirection.DESCENDING);
// Get the previous page by setting the cursor to the "previous"
// cursor from the current page.
options.startCursor(page3.previous);
final Page page2a = getPage(q, options);
System.out.println("Page 2a");
// As the page will be returned in the reverse order because the
// query is reversed, reverse the page for comparison with the
// original.
final Page reverse2a = page2a.reverse();
System.out.println(reverse2a);
// Make sure this page 2 is exactly like the original.
assertEquals(page2, reverse2a);
// Get the previous page by setting the cursor to the "previous"
// cursor from the current page.
options.startCursor(page2a.next);
final Page page1a = getPage(q, options);
System.out.println("Page 1a");
// As the page will be returned in the reverse order because the
// query is reversed, reverse the page for comparison with the
// original.
final Page reverse1a = page1a.reverse();
System.out.println(reverse1a);
// Make sure this page 1 is exactly like the original.
assertEquals(page1, reverse1a);
}