Working with Sequenced Data Objects
Sequenced data objects are SDOs which can track property
ordering across the properties of a data object. They can also
contain unstructured text elements (text element which do not
belong to any of the SDO's properties). Sequenced data objects are
useful for working with XML documents which allow unstructured text (i.e.
mixed=true) or if the elements can be interleaved (
). This can occur for example when
the schema defines maxOccurs>1 on a
element which is a complexType with a choice order indicator.
The examples below assume an SDO created with the following schema
and instance information, using the XML Data Access Service.
The schema below describes the format of a letter. The letter can
optionally contain three properties; date, firstName, and lastName.
The schema states mixed="true" which means that
unstructured text can be interspersed between the three properties.
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:letter="http://letterSchema"
targetNamespace="http://letterSchema">
<xsd:element name="letters" type="letter:FormLetter"/>
<xsd:complexType name="FormLetter" mixed="true">
<xsd:sequence>
<xsd:element name="date" minOccurs="0" type="xsd:string"/>
<xsd:element name="firstName" minOccurs="0" type="xsd:string"/>
<xsd:element name="lastName" minOccurs="0" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:schema>
The following is an instance letter document. It contains the
three letter properties; date, firstName and lastName, and has
unstructured text elements for the address and letter body.
<letter:letters xmlns:letter="http://letterSchema">
<date>March 1, 2005</date>
Mutual of Omaha
Wild Kingdom, USA
Dear
<firstName>Casy</firstName>
<lastName>Crocodile</lastName>
Please buy more shark repellent.
Your premium is past due.
</letter:letters>
When loaded, the letter data object will have the sequence and
property indices shown in the table below:
To ensure sequence indices are maintained, sequenced data objects
should be manipulated through the SDO_Sequence interface.
This allows the data object's instance data to be manipulated
in terms of the sequence index as opposed to the property index
(shown in the table above).
The following examples assume the letter instance has been
loaded into a data object referenced by the variable
$letter.
Example #1 Getting the SDO_Sequence interface
We obtain a data object's sequence using the
getSequence()
method. The follow gets the
sequence for the letter data object.
<?php
$letter_seq = $letter->getSequence();
?>
All subsequent examples assume that the
$letter_seq
variable has been assigned the sequence for the letter data object.
Example #2 Get/set sequence values
We can get and set individual values (including unstructured text)
using the sequence index.
The following sets the firstName to 'Snappy' and gets the last
sequence values (the unstructured text, 'Your premium is past due.').
<?php
$letter_seq[4] = 'Snappy';
$text = $letter_seq[count($letter_seq) - 1];
?>
Example #3 Sequence iteration
We can iterate through the individual sequence values using foreach.
The following runs through the individual values in sequence order.
<?php
foreach ($letter->getSequence() as $value) {
// ...
}
?>
Example #4 Sequence versus Data Object
Setting values through the data object interface may result in the
value not being part of the sequence. A value set through the data
object will only be accessible through the sequence if the property was
already part of the sequence. The following example sets the
lastName through the data object and gets it through the sequence.
This is fine because lastName already exists in the sequence. If
it had not previously been set, then lastName would be set to
'Smith', but would not be part of the sequence.
<?php
$letter[2] = 'Smith';
$last_name = $letter_seq[5];
?>
Example #5 Adding to a sequence
We can add new values to a sequence using the
SDO_Sequence::insert()
method. The following examples assume that the 'firstName' and
'lastName' properties are initially unset.
<?php
// Append a firstName value to the sequence
// value: 'Smith'
// sequence index: NULL (append)
// propertyIdentifier: 1 (firtName property index)
$letter_seq->insert('Smith', NULL, 1);
// Append a lastName value to the sequence
// value: 'Jones'
// sequence index: NULL (append)
// propertyIdentifier: 'lastName' (lastName property name)
$letter_seq->insert('Jones', NULL, 'lastName');
// Append unstructured text
// value: 'Cancel Subscription.'
// sequence index: absent (append)
// propertyIdentifier: absent (unstructured text)
$letter_seq->insert('Cancel Subscription.');
// Insert new unstructured text. Subsequent sequence values
// are shifted up.
// value: 'Care of:'
// sequence index: 1 (insert as second element)
// propertyIdentifier: absent (unstructured text)
$letter_seq->insert('Care of:', 1);
?>
Example #6 Removing from a sequence
We can use the isset() and
unset() functions to test and remove items
from the sequence (Note: unset() currently
leaves the values in the data object, but this behaviour is
likely to change to also remove the data from the data object).
A sequence behaves like a contiguous list; therefore, removing
items from the middle will shift entries at higher indices
down. The following example tests to see if the first sequence
element is set and unsets it if is.
<?php
if (isset($letter_seq[0])) {
unset($letter_seq[0]);
}
?>
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