I shall press ahead with storing the web-safe string of each cursor in
a stack kept in the user's session object, and using this to provide
backwards pagination.
On Jan 17, 8:31 pm, Ian Marshall <ianmarshall...@gmail.com> wrote:
> Does anyone fancy exercising their little grey cells on this fine
> Monday?
>
> I have an entity with relevant fields declared as:
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION,
> detachable = "true")
> public class Thing implements Serializable
> {
> private static final long serialVersionUID = 1L;
>
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> @Extension(vendorName="datanucleus", key="gae.encoded-pk",
> value="true")
> private String sEncodedKey;
>
> @Persistent
> @Extension(vendorName="datanucleus", key="gae.pk-id", value="true")
> private Long loID;
>
> @Persistent
> private Date dtCreated;
>
> }
>
> I want to display pages of my persistent entity to the user, which
> each page having, say, 20 items displayed. I want to use the class
> JDOCursorHelper (and stick with JDO if possible). The GAE/J
> documentation shows me how I can paginate forwards:
>
> · Query the first 21 entities and store in an ArrayList<Thing>.
> · If 21 are returned, set a "there are more entities" flag and
> discard the 21st entity from the list, otherwise reset the flag.
> · Show the 20 entities.
> · Store the cursor as a web-safe string.
> · If the user hits "Next" (enabled if the flag is set) then:
> · retrieve the cursor from the web-safe string.
> · get the next 21 entities
> · etc.
>
> The fun starts if I want to allow the user to paginate the previous
> pages. One method that I can think of stores the web-safe string of
> each cursor in a list kept in the user's session object. As "Next" is
> hit, the cursor just generated can be pushed onto the list. To
> traverse backwards, I pop (delete) the latest cursor string from the
> session's list and then use the previous one (now the latest) to
> produce the previous page's items.
>
> Can anyone think of a smarter way to paginate backwards without
> storing a list of web-safe cursor strings in a user's session?
>
> (I could generate an additional persistent field which holds the
> concatenated string values
>
> [dtCreated to milliseconds using Calendar] + "|" + sEncodedKey
>
> but the GAE/J article for this says that this way is no longer
> recommended.)
>
> Regards,
>
> Ian
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