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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 ( 

<A/><B/><A/>
). 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:

Sequence Index Property Index:Name Value
0 0:date March 1, 2005
1 - Mutual of Omaha
2 - Wild Kingdom, USA
3 - Dear
4 1:firstName Casy
5 2:lastName Crocodile
6 - Please buy more shark repellent.
7 - Your premium is past due.

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.

Przykład #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.

Przykład #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];
?>

Przykład #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) {
    // ...
}
?>

Przykład #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];
?>

Przykład #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);
?>

Przykład #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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