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<concept id="GUID-B756AB28-A0EA-5AA3-86E3-CCFFCD642F08" xml:lang="en"><title>What

are links</title><shortdesc>This topic describes the structure of links. A link is a container

and an element. A link is an item that can be stored in the Comms Database. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>A link is a container. A link refers to another record. A link can be included

in a record. </p>

<p>A link is represented by the templated class <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CMDBRecordLink&lt;T&gt;</apiname></xref>.

The template parameter defines the type of record to which the link refers. </p>

<fig id="GUID-0DFAC1B1-F79B-5C11-8EF3-13E70DBC5984">

<image href="GUID-0FF61B9C-8B0D-5369-B0DA-29AA169B4308_d0e114895_href.png" placement="inline"/>

</fig>

<p>A link is a public data member of a class. The class defines the structure

of record. This record is the 'parent' record of the linked record. For example,

Symbian platform defines the class <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CCDIAPRecord</apiname></xref> that

represents an Internet Access Point (IAP) record. A set of IAP records form

an IAP table. The public data members of this class are the fields and links

that make the record. The following code shows part of the class definition.

Some parts are omitted - this is not the complete class definition. </p>

<codeblock id="GUID-AF4A223F-5A3F-53ED-B797-AB75BB80E174" xml:space="preserve">class CCDIAPRecord : public CCDRecordBase

    {

    public:

        CMDBField<TDesC>                        iServiceType;

        CMDBRecordLink<CCDServiceRecordBase>    iService;

        CMDBField<TDesC>                        iBearerType;

        CMDBRecordLink<CCDBearerRecordBase>     iBearer;

        CMDBRecordLink<CCDNetworkRecord>        iNetwork;

        CMDBField<TUint32>                      iNetworkWeighting;

        CMDBRecordLink<CCDLocationRecord>       iLocation;

        ...

    }

 </codeblock>

<p>A <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CMDBRecordLink&lt;T&gt;</apiname></xref> object contains

an integer. The integer is the <xref href="GUID-6DAF85AD-E412-5823-81C2-FC1755A90A84.dita#GUID-6DAF85AD-E412-5823-81C2-FC1755A90A84/GUID-4DDD4947-D379-5B68-8DC0-B67B074FA852">element

Id</xref> of the linked record in the database. </p>

<p>If you have a parent record in memory, you call the <codeph>LoadL()</codeph> function

on the link object <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CMDBRecordLink&lt;T&gt;</apiname></xref> to

get the linked record into memory. You can access the linked record through

the <codeph>iLinkedRecord</codeph> pointer. This pointer is a member of the <codeph>CMDBRecordLinkBase</codeph> class,

but you can access this data member through the <codeph>CMDBRecordLink&lt;T&gt;</codeph> object. </p>

<p>There are two cases: </p>

<ul>

<li id="GUID-EB395834-73F0-592B-ADB0-0DB6499B534C"><p>If you know what type

of record the link refers to you cast the pointer to the correct type. For

example: </p> <codeblock id="GUID-A72D6DD6-31F4-5CB9-8688-810E33250DC7" xml:space="preserve">CCDDialOutISPRecord* ptrIspRecord = static_cast&lt;CCDDialOutISPRecord*&gt;(ptrSingleIAPRecord-&gt;iService.iLinkedRecord);</codeblock> <p>where <codeph>ptrSingleIAPRecord</codeph> is of type <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CCDIAPRecord</apiname></xref>. </p> </li>

<li id="GUID-A1E77CBE-3E79-55A1-9FA2-3CFF55C9FADB"><p>If you do not know what

type of record the link refers to you cast the pointer to the base class for

records. You use <codeph>GetFieldByNameL()</codeph> or <codeph>GetFieldByIdLaccess()</codeph> to

access the data in the linked record. For example: </p> <codeblock id="GUID-684703C6-0754-5F69-91E1-6ED1202A0895" xml:space="preserve">CCDServiceRecordBase* ptrServiceRecord = static_cast&lt;CCDServiceRecordBase*&gt;(ptrSingleIAPRecord-&gt;iService.iLinkedRecord);

CMDBField<TUint32>* field; 

// Find a field by its Id. In this code fragment, the field we are looking for 

// is the bearer speed field.

field = (CMDBField&lt;TUint32&gt;*)ptrServiceRecord-&gt;GetFieldByIdL(KCDTIdBearerSpeed);</codeblock> </li>

</ul>

</conbody><related-links>

<link href="GUID-9D56FF77-A20B-5BFB-8DE6-19CC4535DFED.dita"><linktext>Following

                a link to another table and finding a field by Id and by name:

Tutorial</linktext></link>

</related-links></concept>