Apple Newton Utilities Podręcznik Użytkownika Pobierz pdf (Strona 473)

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CHAPTER 11

Data Storage and Retrieval

Using Newton Data Storage Objects 11-41

at or before the position that would be occupied by 27 in the index is the last entry

in the range over which the cursor iterates.

To conduct the same query while excluding the endrange values, specify a

beginExclKey value instead of a beginKey value, and specify an endExclKey

value instead of an

endKey value, as shown in the following code fragment:

// mySoup is indexed on the 'number slot

// return entries for which (11 > entry.number < 27 )

local numCursor := mySoup:Query({indexPath: 'number,

beginExclKey: 11,

endExclKey: 27});

Note that a query spec cannot include both the inclusive and exclusive forms of the

same endrange selector; for example, you cannot specify

beginKey and a

beginExclKey values in the same query spec. However, you can specify, for

example, a

beginKey value and an endExclKey value in the same query spec.

Because the index sorts entries according to key values, a

beginKey on a soup

indexed in descending key order may appear to act like an

endKey on a soup

indexed in ascending order, and vice versa. For more information, see “Queries on

Descending Indexes” beginning on page 11-46.

Another way to ﬁnd all entries having a particular value in a speciﬁed slot is to use

indexValidTest method, which can test any index key value without reading

its corresponding entry into the NewtonScript heap. The system passes index key

values to this function as the cursor moves. Your

indexValidTest must return a

non-

nil value if the entry associated with the key value should be included in the

query result. For example, you could use an

indexValidTest method to select

entries that hold even-number values in a speciﬁed slot, as shown in the following

code fragment:

// mySoup indexed on 'number slot

// select entries having a 'number slot that holds

// an even value between 19 and 58

local myCursor :=

mySoup:Query({ beginKey: 19, endExclKey: 58,

indexValidTest: func (key)

(key MOD 2 = 0)});

A less-preferred way to test entries is to provide a validTest function to test

entries individually. The use of a

validTest increases the memory requirements

of the search because the system must read soup entries into the NewtonScript heap

in order to pass them to the

validTest function. Whenever possible, you should

avoid using

validTest methods in favor of using indexValidTest methods.

Generally, you need not use a

validTest method unless you must read the

entry’s data to determine whether to include it in the query result.

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