Apple Newton Utilities Guide de l'utilisateur télécharger pdf (Page 472)

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CHAPTER 11

Data Storage and Retrieval

11-40 Using Newton Data Storage Objects

particular slot, the soup must be indexed on that slot. For example, the following

example of a query returns a cursor to all soup entries that have a

name slot. The

cursor sorts the entries according to the value of this slot. As ﬁrst returned by the

query, the cursor points to the ﬁrst entry in index order.

// mySoup is a valid soup indexed on the 'name slot

nameCursor:= mySoup:Query({indexPath:'name});

You can also use the cursor method GoToKey to go directly to the ﬁrst entry

holding a speciﬁed name or value in an indexed slot. For examples of the use of

this method, see “Moving the Cursor” beginning on page 11-55.

Using

beginKey and endKey values to limit your search can improve query

performance signiﬁcantly. The following example is an index query that uses

beginKey value and an endKey value to return entries for which

(11 ≥ entry.number ≤ 27 ).

// mySoup is indexed on the 'number slot

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

beginKey: 11,

endKey: 27});

The index on the number slot potentially includes all entries that have a number

slot. The index sorts entries on their index key values; unless otherwise speciﬁed,

the default index order is ascending. Thus, the query can use a

beginKey value of

11 to skip over entries holding a value less than 11 in the number slot. The test

can be concluded quickly by specifying a maximum value beyond which the cursor

generated by this query does not proceed. In this case, the

endKey value speciﬁes

that the query result does not include entries having values greater than

27 in the

number slot. When multiple entries hold a specified endrange value, all of them

are included in the result of a query that speciﬁes that endrange value; for example,

if multiple entries in the

mySoup soup hold the value 27 in their number slot, the

previous example includes all of these entries in its result.

The

beginKey speciﬁcation evaluates to a value that occupies a unique position in

the sorted index data for the soup. If no entry is associated with this value, the

cursor is positioned at the next valid entry in index order. For example, if the

mySoup

soup in the previous code fragment does not contain an entry having a

number slot

that holds the value

11, the next valid entry in index order is the ﬁrst entry in the

range over which the cursor iterates.

Similarly, the

endKey speciﬁcation evaluates to a value that occupies a unique

position in the sorted index data for the soup. If no entry is associated with this

value, the cursor stops on the ﬁrst valid entry in index order before the

endKey

value. For example, if the

mySoup soup in the previous code fragment does not

contain an entry having a

number slot that holds the value 27, the last valid entry

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Apple Newton Utilities Guide de l'utilisateur Page 472

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