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CHAPTER 11

Data Storage and Retrieval

11-10 About Data Storage on Newton Devices

data from a different locale. To take advantage of this behavior, the application

must create an internationalized index for the soup and the query must request the

alternate sorting behavior explicitly in its query spec. For more information, see

“Internationalized Sorting Order for Text Queries” on page 11-45.

Saving User Preference Data in the System Soup 11

Most of the time you’ll want to store data in union soups, but one task for which

union soups are not suitable is the storage of your application’s user preferences

data. There are several good reasons for always saving user preferences data on the

internal store:

■ If your application is on a card that is moved from one Newton device to another,

it acts the way the users of the respective Newton devices think it should.

■ It rarely makes sense to distribute preferences data among several storage cards.

■ It’s difﬁcult to guarantee that your application will always have access to any

particular card.

■ If your application is on the internal store and it simply adds preference data to

the default store, the preference data could be saved on an external store that

becomes unavailable to the application when a card is ejected.

Hence, the built-in

ROM_SystemSoupName soup on the internal store is usually

the ideal place to keep your application’s preference data. The

GetAppPrefs

function allows you to get and set your application’s preferences frame in this

soup. For more information, see the description of this function in Chapter 26,

“Utility Functions.” For more information about the

ROM_SystemSoupName soup

itself, see Chapter 19, “Built-in Applications and System Data.”

Queries 11

To retrieve entries from a soup or union soup, you perform a query by sending the

Query message to the soup or union soup. The Query method accepts as its

argument a frame known as a query speciﬁcation or query spec. The query spec

deﬁnes criteria for the inclusion of entries in the query result. You can think of the

query spec as a ﬁlter that the

Query method uses to select a subset of the soup’s

data. Queries can test index key values or string values and perform customized

tests that you deﬁne.

A single query spec can specify multiple criteria that entries must meet in order to

be included in the result of the query. For example, you can specify that your query

return all entries created after a certain date that are tagged

'business but do not

contain the

"paid" string. For instructional purposes, this chapter discusses

separately each test that a query spec may include.

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