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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

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

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

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

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

    16 in a record. </p>

    17 <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>.

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

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

    20 <image href="GUID-0FF61B9C-8B0D-5369-B0DA-29AA169B4308_d0e86440_href.png" placement="inline"/>

    21 </fig>

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

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

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

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

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

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

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

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

    30     {

    31     public:

    32         CMDBField<TDesC>                        iServiceType;

    33         CMDBRecordLink<CCDServiceRecordBase>    iService;

    34         CMDBField<TDesC>                        iBearerType;

    35         CMDBRecordLink<CCDBearerRecordBase>     iBearer;

    36         CMDBRecordLink<CCDNetworkRecord>        iNetwork;

    37         CMDBField<TUint32>                      iNetworkWeighting;

    38         CMDBRecordLink<CCDLocationRecord>       iLocation;

    39         ...

    40     }

    41  </codeblock>

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

    43 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

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

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

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

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

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

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

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

    51 <ul>

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

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

    54 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>

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

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

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

    58 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);

    59 CMDBField<TUint32>* field; 

    60 

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

    62 // is the bearer speed field.

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

    64 </ul>

    65 </conbody><related-links>

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

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

    68 Tutorial</linktext></link>

    69 </related-links></concept>