io.ebean

Interface PagedList<T>

Type Parameters:

T - the entity bean type

public interface PagedList<T>

Represents a page of results.

The benefit of using PagedList over just using the normal Query with Query.setFirstRow(int) and Query.setMaxRows(int) is that it additionally wraps functionality that can call Query.findFutureCount() to determine total row count, total page count etc.

Internally this works using Query.setFirstRow(int) and Query.setMaxRows(int) on the query. This translates into SQL that uses limit offset, rownum or row_number function to limit the result set.

Example: typical use including total row count

    // We want to find the first 50 new orders
    //  ... so we don't really need setFirstRow(0)

    PagedList<Order> pagedList
      = ebeanServer.find(Order.class)
      .where().eq("status", Order.Status.NEW)
      .order().asc("id")
      .setFirstRow(0)
      .setMaxRows(50)
      .findPagedList();

    // Optional: initiate the loading of the total
    // row count in a background thread
    pagedList.loadRowCount();

    // fetch and return the list in the foreground thread
    List<Order> orders = pagedList.getList();

    // get the total row count (from the future)
    int totalRowCount = pagedList.getTotalRowCount();

Example: No total row count required

    // If you are not getting the 'first page' often
    // you do not bother getting the total row count again
    // so instead just get the page list of data

    // fetch and return the list in the foreground thread
    List<Order> orders = pagedList.getList();

See Also:

Query.findPagedList()

Method Summary

Modifier and Type	Method and Description
String	getDisplayXtoYofZ(String to, String of) Helper method to return a "X to Y of Z" string for this page where X is the first row, Y the last row and Z the total row count.
Future<Integer>	getFutureCount() Return the Future row count.
List<T>	getList() Return the list of entities for this page.
int	getPageIndex() Return the index position of this page (Zero based).
int	getPageSize() Return the page size used for this query.
int	getTotalCount() Return the total row count for all pages.
int	getTotalPageCount() Return the total number of pages based on the page size and total row count.
boolean	hasNext() Return true if there is a next page.
boolean	hasPrev() Return true if there is a previous page.
void	loadCount() Initiate the loading of the total row count in the background.

Method Detail

loadCount

void loadCount()

Initiate the loading of the total row count in the background.

    // initiate the loading of the total row count
    // in a background thread
    pagedList.loadRowCount();

    // fetch and return the list in the foreground thread
    List<Order> orders = pagedList.getList();

    // get the total row count (from the future)
    int totalRowCount = pagedList.getTotalRowCount();

Also note that using loadRowCount() and getTotalRowCount() rather than getFutureRowCount() means that exceptions ExecutionException, InterruptedException, TimeoutException are instead wrapped in the unchecked PersistenceException (which might be preferrable).

getFutureCount

Future<Integer> getFutureCount()

Return the Future row count. You might get this if you wish to cancel the total row count query or specify a timeout for the row count query.

The loadRowCount() & getTotalRowCount() methods internally make use of this getFutureRowCount() method. Generally I expect people to prefer loadRowCount() & getTotalRowCount() over getFutureRowCount().

    // initiate the row count query in the background thread
    Future<Integer> rowCount = pagedList.getFutureRowCount();

    // fetch and return the list in the foreground thread
    List<Order> orders = pagedList.getList();

    // now get the total count with a timeout
    Integer totalRowCount = rowCount.get(30, TimeUnit.SECONDS);

    // or ge the total count without a timeout
    Integer totalRowCountViaFuture = rowCount.get();

    // which is actually the same as ...
    int totalRowCount = pagedList.getTotalRowCount();

getList

List<T> getList()

Return the list of entities for this page.

getTotalCount

int getTotalCount()

Return the total row count for all pages.

If loadRowCount() has already been called then the row count query is already executing in a background thread and this gets the associated Future and gets the value waiting for the future to finish.

If loadRowCount() has not been called then this executes the find row count query and returns the result and this will just occur in the current thread and not use a background thread.

    // Optional: initiate the loading of the total
    // row count in a background thread
    pagedList.loadRowCount();

    // fetch and return the list in the foreground thread
    List<Order> orders = pagedList.getList();

    // get the total row count (which was being executed
    // in a background thread if loadRowCount() was used)
    int totalRowCount = pagedList.getTotalRowCount();

getTotalPageCount

int getTotalPageCount()

Return the total number of pages based on the page size and total row count.

This method requires that the total row count has been fetched and will invoke the total row count query if it has not already been invoked.

getPageSize

int getPageSize()

Return the page size used for this query. This is the same value as maxRows used by the query.

getPageIndex

int getPageIndex()

Return the index position of this page (Zero based).

This is a calculated value based on firstRow/maxRows.

hasNext

boolean hasNext()

Return true if there is a next page.

This method requires that the total row count has been fetched and will invoke the total row count query if it has not already been invoked.

hasPrev

boolean hasPrev()

Return true if there is a previous page.

getDisplayXtoYofZ

String getDisplayXtoYofZ(String to,
                         String of)

Helper method to return a "X to Y of Z" string for this page where X is the first row, Y the last row and Z the total row count.

This method requires that the total row count has been fetched and will invoke the total row count query if it has not already been invoked.

Parameters:

to - String to put between the first and last row

of - String to put between the last row and the total row count

Returns:

String of the format XtoYofZ.