Apple Newton Utilities Uživatelská příručka stáhnout pdf (Strana 448)

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CHAPTER 11

Data Storage and Retrieval

11-16 About Data Storage on Newton Devices

unless this behavior is requested explicitly, the words "blackSmith" and

"Smithsonian" would also be found by this query.

A text query is slower than its words query counterpart. Text queries do not require

signiﬁcantly more heap space than other kinds of queries.

For more information about performing text queries, see “Querying for Text”

beginning on page 11-43.

Cursors 11

The Query method returns a cursor, which is an object that iterates over the set of

entries satisfying the query spec and returns entries in response to the messages it

receives. Cursors return entries in index key order. As entries in the soup are added,

deleted, and changed, the set of entries the cursor references is updated

dynamically, even after the original query has been performed.

Recall that after selecting a subrange of all entries in the soup, a query can use

various tests to eliminate certain entries within that range. If viewed within the

context of the entire soup index, the ﬁnal set of valid entries is discontiguous—that

is, it includes gaps occupied by entries that did not meet the criteria established by

the query spec. However, the cursor presents this subset as a continuous range of

entries, as depicted in Figure 11-5.

Initially, the cursor points to the ﬁrst entry in index order that satisﬁes the query.

The cursor supplies methods that allow you to determine its current position, retrieve

the entry referenced by its current position, or specify a new position. The cursor

may be moved incrementally, moved to the position occupied by a speciﬁed entry

or key, or reset to an initial position that is not necessarily the ﬁrst entry in the valid

set. Note that it is possible to move the cursor incrementally to a position outside

the valid range of entries, in which case the cursor returns

nil instead of an entry.

For information about using cursors, see “Using Cursors” beginning on page 11-53.

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