Apple Newton Utilities Podręcznik Użytkownika Pobierz pdf (Strona 488)

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CHAPTER 11

Data Storage and Retrieval

11-56 Using Newton Data Storage Objects

You can use the Move method to move the cursor multiple positions. For example,

instead of coding incremental cursor movement as in the following example,

for i := 1 to 5 do myCursor:Next();

you can obtain faster results by using the Move method. The following code

fragment depicts a typical call to this method. After positioning the cursor, the

Move method returns the current entry.

// skip next four entries and return the fifth one or nil

local theEntry := myCursor:Move(5);

To move the cursor in large increments, it’s faster to use the GoTo and GoToKey

methods to position the cursor directly. You can use the

GoToKey method to go

directly to the ﬁrst indexed slot that has a particular value and return the entry

containing that slot, as shown in the following example:

// index spec for soup that generated myCursor

indxSpec: {structure: 'slot, path: 'name, type: 'string};

// go to the first entry that has

// the value "Nige" in the name slot

local theEntry := myCursor:GotoKey("Nige");

If the argument to the GoToKey method is not of the type speciﬁed by the soup’s

index spec, this method throws an exception. For example, the index spec in the

previous example speciﬁes that the

name slot holds string data. If you pass a

symbol to the

GoToKey method, it signals an error because this soup’s index holds

string data:

// throws exception - arg doesn’t match index data type

myCursor:GotoKey('name);

Counting the Number of Entries in Cursor Data 11

Because the user can add or delete entries at any time, it’s difﬁcult to determine

with absolute certainty the number of entries referenced by a cursor. With that in

mind, you can use the

CountEntries cursor method to discover the number of

entries present in the set referenced by the cursor at the time the

CountEntries

method executes.

To discover the number of entries in the entire soup, you can execute a very broad

query that includes all soup entries in the set referenced by the cursor and then

send a

CountEntries message to that cursor. For example:

local allEntriesCursor := mySoup:Query(nil);

local numEntries := allEntriesCursor:CountEntries();

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