Data Storage and Retrieval

Using Newton Data Storage Objects

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.

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.

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");