Apple Newton Utilities Betriebsanweisung PDF herunterladen (Seite 479)

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CHAPTER 11

Data Storage and Retrieval

Using Newton Data Storage Objects 11-47

Sending the Reset message to the cursor positions it at the ﬁrst valid entry in

index order. In this case, the ﬁrst entry is

"noun" because the entries are sorted in

descending alphabetical order.

The

GoToKey cursor method steps through the set of valid entries in index order

until it ﬁnds the ﬁrst entry having a speciﬁed key value. If the speciﬁed key value is

not found, this method returns the next valid entry found after the speciﬁed index

position. Thus, sending the

GotoKey("az") message to this cursor returns the

value

"axe" because it’s the ﬁrst valid entry that appears in the index after the

unoccupied

"az" position.

Sending the

GotoKey("a") message to this cursor returns the value nil because

this message positions the cursor beyond the end of the range of valid entries

deﬁned by the query that generated the cursor.

Figure 11-7 illustrates that specifying a

beginExclKey value of "b" excludes

from consideration every entry beginning with a letter that comes after

"b" in the

reverse alphabet; that is, this

beginExclKey value causes the valid range of

entries to include only entries beginning with

"a". As a result, sending the

GotoKey("n") message causes this cursor to return the value "axe" because it

is the ﬁrst valid entry appearing in the index after the

"n" position.

Note

The sort order for symbol-based indexes is the ASCII order of the

symbol’s lexical form. This sorting behavior is made available in

NewtonScript by the

SymbolCompareLex global function. ◆

Figure 11-7 Specifying ends of a descending index

Querying on Multiple-Slot Indexes 11

Before reading this section, you should understand the contents of “Querying on

Single-Slot Indexes” beginning on page 11-39.

Descending key order

beginExclKey cursor:GoToKey("n");

Valid subrange

Z "noun" "name" BN "axe" "able" A

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