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CHAPTER 11

Data Storage and Retrieval

About Data Storage on Newton Devices 11-23

Null Union Soups 11

Under unusual circumstances a 1.x application may encounter a union soup that

doesn’t contain any member soups. A soup in this state is referred to as a null

union soup. Queries on a null union soup fail. Attempts to add entries to a missing

member soup also fail if a soup deﬁnition for that soup has not been registered.

Null union soups should not normally occur with 1.

x applications and cannot occur

with applications that use the 2.0 union soup interface correctly.

Null union soups are most often found in the aftermath of a debugging session—

for example, if in the NTK Inspector you have deleted various soups (to test the

cases in which your application needs to create its own soups) and neglected to

restore things to their normal state.

Null union soups can also occur as a result of the application soup not being

created properly. Normally, when a card is ejected, the internal store member of a

union soup is left behind or a soup deﬁnition for creating that soup is available.

When this is not the case, the union soup reference to the internal store member is

null when the card is ejected. If you follow the guidelines outlined in “Registering

and Unregistering Soup Deﬁnitions” on page 11-33 this problem does not occur.

Null union soups can also occur when another application deletes one or more

soups that your application uses. Any application that deletes soups should at least

transmit a soup change notiﬁcation, thereby allowing your application to deal with

the change appropriately.

When your application is running on a 1.

x unit or when no soup deﬁnition exists

for a union soup, it is appropriate to test for a constituent soup’s validity before

trying to add an entry to it. Simply loop through the array of stores returned by the

GetStores function, sending the IsValid message to each of the constituent

soups in the union.

Query Compatibility Information 11

Version 2.0 of Newton system software provides a more powerful query mechanism

while at the same time simplifying the syntax of queries. Although old-style query

syntax is still supported, you’ll probably want to revise your application code to

take advantage of the features new-style queries provide. The following list

summarizes changes to queries. The remainder of this section explores query

compatibility issues in more detail.

Query (soupOrUSoup, querySpec) // use soupOrUSoup:Query(querySpec) instead

querySpec := {type : symbol, // obsolete, do not use

startKey: keyValue, // use beginKey or beginExclKey

endTest: keyValue, // endKey or endExclKey instead

… }

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