Apple Newton Utilities User's Guide download pdf (Page 471)

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CHAPTER 11

Data Storage and Retrieval

Using Newton Data Storage Objects 11-39

■ the use of internationalized sorting order

■ queries on multiple-slot indexes

Querying Multiple Soups 11

Soups having the same name can be associated logically by a union soup object. To

retrieve entries from all the available soups in a union, just send the

Query

message to the union soup object.

You must query differently named soups separately, however. For example, before

scheduling a meeting, you might send the

Query message to the

ROM_CardfileSoup soup for information regarding its participants, and send

another

Query message to the ROM_CalendarSoupName soup to determine

whether you have conﬂicting appointments at the proposed meeting time.

Entry aliases provide a handy way to save references to soup entries. You can use

entry aliases to reference entries from different soups more easily. For more

information, see “Using Entry Aliases” on page 12-7.

Querying on Single-Slot Indexes 11

This section provides code examples illustrating a variety of queries on single-slot

indexes. For more information on indexes, see “Introduction to Data Storage

Objects” on page 11-2 and “Indexes” on page 11-8.

The following code fragment presents an example of the simplest kind of index

query—it returns all entries in the soup:

local myUSoup := GetUnionSoupAlways("mySoup:mySig");

local allEntriesCursor := myUSoup:Query(nil);

When nil is passed as the query spec, as in the example above, the query result

potentially includes all entries in the soup. The cursor generated by such a query

returns entries in roughly the same order that they were added to the soup;

however, this sorting order is not guaranteed because the system recycles the values

it uses to identify entries internally. The only way to guarantee that entries are

sorted in the order they were added to a soup is to index them on your own time

stamp slot.

Most situations will require that you query for a subset of a soup’s entries, rather

than for all of its entries. That is, you’ll want to include or exclude entries

according to criteria you deﬁne. For example, you might want to ﬁnd only entries

that have a certain slot, or entries in which the value of a speciﬁed slot falls within

a certain range. The next several examples illustrate the use of single-slot index

queries for these kinds of operations.

To ﬁnd all entries that have a particular slot, specify a path to that slot as the query

spec’s

indexPath value. Note that in order to query on the presence of a

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