background image
C H A P T E R 1 1
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
a
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
© 2007-2017, o7 studio » при воспроизведении материала сайта ссылка обязательна