Apple Newton Utilities Podręcznik Użytkownika Pobierz pdf (Strona 456)

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CHAPTER 11

Data Storage and Retrieval

11-24 About Data Storage on Newton Devices

Query Global Function Is Obsolete 11

Queries are now performed by the Query method of soups or union soups;

however, the

Query global function still exists for compatibility with applications

using version 1.

x of the Newton application programming interface. The Query

method accepts the same query speciﬁcation frame argument that the

Query

global function did; however, version 2.0 query specs provide additional features

that 1.

x queries do not. For examples of the use of the Query method, see “Using

Queries” beginning on page 11-38. For a complete description of the query spec

frame and its slots, see “Query Speciﬁcation Frame” (page 9-9) in Newton

Programmer’s Reference.

Query Types Obsolete 11

Query specs no longer require a type slot; if this slot is present, it is ignored.

StartKey and EndTest Obsolete 11

Because the order in which the cursor returns entries is determined entirely by

index values, specifying key values is sufﬁcient to determine a range. Hence, the

use of an

endTest function in a query spec is always unnecessary. Instead, your

query spec should specify an

endKey or endExclKey value.

The

endTest function was sometimes used for other purposes, such as stopping

the cursor after the visible portion of a list had been ﬁlled; however, this sort of test

is best performed outside the cursor to optimize performance. The caller of the

cursor’s

Next method should be able to determine when to stop retrieving soup

entries without resorting to the use of an

endTest function.

When a cursor is generated initially and when it is reset, it references the entry

having the lowest index value in the set of entries in the selected subset. Thus, it is

usually unnecessary to use a start key, although this operation still works as in

earlier versions of system software. For those occasions when it is necessary to

start the cursor somewhere in the middle of the range, the use of a start key can be

simulated easily by invoking the cursor’s

GotoKey method immediately after

generating or resetting the cursor.

Queries on Nil-Value Slots Unsupported 11

In Newton system software prior to version 1.05, storing a value of nil in the

indexed slot of an entry returns

nil to the query for that entry; that is, the query

fails to ﬁnd the entry. To work around this problem in older Newton systems, make

sure your indexed slots store appropriate values.

In Newton system software version 2.0, the behavior of queries on

nil-value slots

is unspeciﬁed. For best performance, make sure your indexed slots store

appropriate values.

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