Apple Newton Utilities Betriebsanweisung PDF herunterladen (Seite 474)

100

101

CHAPTER 11

Data Storage and Retrieval

11-42 Using Newton Data Storage Objects

The query passes the entire entry to the validTest method, rather than just the

value of the indexed slot. The next code example reads the entry’s

aSlot and

otherSlot slots in order to compare their values:

// select entries for which aSlot > otherSlot

local myCursor :=

mySoup:Query({endKey: aKeyValue,

validTest: func (entry)

begin

entry.aSlot > entry.otherSlot

end});

Querying for Tags 11

In order to select soup entries according to their associated tag values, you need to

include a tags query spec frame in the

tagSpec slot of the query speciﬁcation

frame passed to the

Query method. In addition to specifying one or more tags used

to select entries, the tags query spec can specify set operators such as

not, any,

equal, and all to create complex filters based on tag values. For a complete

description of the tags query spec frame, see “Tags Query Speciﬁcation Frame”

(page 9-13) in Newton Programmer’s Reference.

You cannot query for tags on a soup that does not have a tags index. This index is

usually speciﬁed by your soup deﬁnition and created along with the soup, but it can

be added to an existing soup if necessary. Note that each soup or union soup has

only one tags index; if you add a tags index to a soup that already has one, it

replaces the original tags index. For more information, see “Tags Index

Speciﬁcation Frame” (page 9-8) in Newton Programmer’s Reference.

The next several examples presume that the

mySoup soup has a tags index on the

labels slot. Note that queries need not specify the path to the slot from which tag

values are extracted—in this case, the

labels slot—because each soup has only

one tags index and its index path is speciﬁed when the tags index is created.

However, because a soup or union soup is allowed to have multiple soup indexes,

queries must specify a path to the indexed slot; hence, these examples also presume

that the

mySoup soup has a soup index on the name slot.

The presence of any tag speciﬁed by the

any set operator is sufﬁcient to include its

entry in the results of the query that uses this operator. For example, the following

query selects entries having either the symbol

'flower or 'tall in the labels

slot. Entries not marked with at least one of these symbols are not included in the

query result.

local myCurs := mySoup:Query({indexPath:'name,

tagSpec: {any:['tall, 'flower]}});

The equal set operator speciﬁes a set of tags an entry must match exactly to be

included in the query result. The query in the following example uses the

equal

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