Apple Newton Utilities Guia do Utilizador descarregar pdf (Página 470)

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CHAPTER 11

Data Storage and Retrieval

11-38 Using Newton Data Storage Objects

This approach provides the following beneﬁts:

■ It prevents your application from inadvertently damaging another

application’s data.

■ It helps your application avoid name conﬂicts with other applications’ slots.

■ It prevents soups from becoming cluttered with excessive numbers of entries.

■ It facilitates removal of your application’s data.

Note that when you makes changes to other applications’ soups you should

transmit notiﬁcation of the changes by means of the mechanism described in

“Using Soup Change Notiﬁcation” beginning on page 11-63.

Adding Tags to an Existing Soup 11

You can add tags only to a soup that has a tags index. To add new tags to a soup

that already has a tags index, simply add to the soup an entry that uses the new

tags—the tags index is updated automatically to include the new tags.

Adding a tags index to an existing soup is like adding any other kind of index:

simply pass the appropriate index spec to the soup’s

AddIndexXmit method.

Remember, however, that the system allows only one tags index per soup. If you try

to add another tags index to that soup, you’ll replace the original tags index. It’s

quite easy to add new tags to a soup that already has a tags index, so you’ll rarely

need to replace a soup’s tags index.

Using Queries 11

To retrieve soup entries, you need to query a soup or union soup object by sending

the

Query message to it. The Query method accepts a query speciﬁcation frame,

or query spec, as its argument. The query spec speciﬁes the characteristics that

soup entries must have in order to be included in the query result.

Note

For instructional purposes, this section describes each item that

may appear in a query speciﬁcation separately. Normally, a single

query spec deﬁnes multiple criteria that soup entries must meet to

be included in the results of the query; for example, you can

create a single query spec that speciﬁes tests of index key values,

string values, and tags.

◆

This section describes how to perform various queries to retrieve soup data. It

includes examples of

■ simple queries on index values, tags, or text

■ the use of ascending and descending indexes

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