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<task xml:lang="en" id="GUID-9D56FF77-A20B-5BFB-8DE6-19CC4535DFED"><title>Following a link to another table and finding a field by Id and by name: Tutorial</title><shortdesc>This tutorial shows you how to follow a link to a Symbian OS defined table. The tutorial also shows two methods to get the value of a field. </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody> <prereq id="GUID-E4B235C3-CD22-57E0-BC48-DDDB0A6AFFFC"><p>Before you start, you must understand: </p> <ul><li id="GUID-6C352504-E6D4-5C17-88A3-1563F3AEE53E"><p>the general concept of the Comms Database </p> </li> <li id="GUID-AC4D044B-3B8E-522A-AB9D-5EBA1BCCE299"><p>the specific concept of fields, records, links and tables </p> </li> <li id="GUID-51754AAB-7EE7-5FB4-869C-7FADD29951D9"><p>how to write and build application code to run on Symbian OS </p> </li> </ul> </prereq> <context id="GUID-A7FE99ED-D5CC-5F71-8B64-E0CCB1F8222E"><p>The tutorial shows you how to follow a link from a record in the <xref href="GUID-387A8240-0765-52F2-98A4-8F9FC809E03E.dita#GUID-387A8240-0765-52F2-98A4-8F9FC809E03E/GUID-57197DDE-9DE0-5978-8F2F-D2E370489E3C">IAP</xref> table to a record in the service table. The tutorial then shows you how to find the "Bearer Speed" field by its Id and by its name in the linked record. </p> <p>The principles that apply here also apply to the other Symbian OS defined tables </p> </context> <steps id="GUID-02024A4A-F0D7-5EC0-BB5C-8BCC12D33BBB"><step id="GUID-FEB0F22C-F0F7-575F-9063-0D21D6708021"><cmd>Make sure that you have created a session. </cmd> </step> <step id="GUID-D7D8189E-EE40-5305-B993-26D9F28D3EC5"><cmd>Create the IAP record object in the tool or application process and prime it for the search for the service type "DialOutISP". </cmd> <info>Symbian OS defines the <codeph>CCDIAPRecord</codeph> class to represent a <xref href="GUID-387A8240-0765-52F2-98A4-8F9FC809E03E.dita#GUID-387A8240-0765-52F2-98A4-8F9FC809E03E/GUID-57197DDE-9DE0-5978-8F2F-D2E370489E3C">IAP</xref> record. The class is a schema for the record. The class defines the fields and links that make a IAP record. </info> <info>Symbian OS defines <xref href="GUID-6DAF85AD-E412-5823-81C2-FC1755A90A84.dita#GUID-6DAF85AD-E412-5823-81C2-FC1755A90A84/GUID-32E556BC-55C3-5FBD-9A60-9708139C20D6">unique numeric Id</xref> s for Symbian OS defined tables. The symbol <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>KCDTIdIAPRecord</apiname></xref> defines the value of this Id for the IAP table. The Id allows the CommsDat API to retrieve the table from the Comms Database efficiently. </info> <stepxmp><codeblock id="GUID-31732ADA-3BC7-5D6E-8579-6CE700C2A9B7" xml:space="preserve">...

// Create a single IAP record in memory and prime it with the type of service

// that you want to find. In this case, the type of service is "DialOutISP".

// This code fragment assumes that a session with the Comms Database has been created.

// "iDb" is a pointer to a CMDBSession object

_LIT(KISPType, "DialOutISP");

TUint32 bearerSpeed;

// Use the factory function CCDRecordBase::RecordFactoryL() to create the IAP record obejct. 

//

// Note:

// 1. the template parameter CCDIAPRecord defines 

//    the "IAP" record type.

// 2. the unique numeric Id KCDTIdIAPRecord is passed as a parameter

//    to the constructor.

CCDIAPRecord* ptrSingleIAPRecord = static_cast<CCDIAPRecord*>(CCDRecordBase::RecordFactoryL(KCDTIdIAPRecord)); 

// The storage for string or binary fields must be allocated

// explicitly if set or reset by the application. Storage required for

// storing data  retrieved from the database is handled by the implementation of the CommsDat API.

//

// Set the service type.

ptrSingleIAPRecord->iServiceType.SetMaxLengthL(KISPType().Length());

ptrSingleIAPRecord->iServiceType = KISPType; 

// Note that you can replace the above two function calls with the 

// single function call:

//

// ptrSingleIAPRecord->iServiceType.SetL(KISPType); 

...</codeblock> </stepxmp> </step> <step id="GUID-A661444B-A268-56C5-81FF-B3AB0063BA9C"><cmd>Search for the first IAP record that has "DialOutISP" as the service type. If the record is found, load the associated service table record. </cmd> <stepxmp><codeblock id="GUID-E197DCA4-4E3D-5963-A548-8FD84F797C6B" xml:space="preserve">...

if(ptrSingleIAPRecord->FindL(*iDb))

    { 

    // An IAP record with "DialOutISP" as the service type has

    // been found and loaded into memory. 

    // Load the service table record associated with this IAP.

    ptrSingleIAPRecord->iService.LoadL(*iDb);

    ...</codeblock> </stepxmp> </step> <step id="GUID-5A28A3C4-BB43-52BF-8F98-00B125549A45"><cmd/><substeps id="GUID-B20735EC-2966-5C31-9591-8108A0A4BB5C"><substep id="GUID-76112AFB-54C4-55D8-AC6E-1B9D86CC35A7"><cmd>CASE 1 : Access the service record when you know the service type. This is the most effiecient method. </cmd> <stepxmp><codeblock id="GUID-316366CE-97B7-5093-8480-2AA021F764D5" xml:space="preserve">

    ...

    CCDDialOutISPRecord* ptrIspRecord = static_cast<CCDDialOutISPRecord*>(ptrSingleIAPRecord->iService.iLinkedRecord);

    bearerSpeed = ptrIspRecord->iBearerSpeed;

    ...</codeblock> </stepxmp> </substep> <substep id="GUID-2A8FE5F5-D7AD-5F95-A2D5-AD6DA1C4EDA0"><cmd>CASE 2: Access the service record when you do not know the service type. This is also the more general case and is slower than case 1. </cmd> <info>You can find a field by its Id, or you can find a field by its name. To find a field by its name is not recommended, because this operation is slow. </info> <stepxmp><codeblock id="GUID-0FDC8EF4-45FF-542B-87FD-042FC31F431C" xml:space="preserve">

    ...

    // Use the base class "CCDServiceRecordBase" instead of the more specific

    // class "CCDDialOutISPRecord" [or any other specific class derived from "CCDServiceRecordBase"].

    CCDServiceRecordBase* ptrServiceRecord = static_cast<CCDServiceRecordBase*>(ptrSingleIAPRecord->iService.iLinkedRecord);

    CMDBField<TUint32>* field; 

    ...

    // Find a field by its Id

    field = (CMDBField<TUint32>*)ptrServiceRecord->GetFieldByIdL(KCDTIdBearerSpeed);

    bearerSpeed = *field;

    ...

   // Find a field by its name. Symbian OS defines KCDTypeNameBearerSpeed to represent 

   // the name of the field.

    TPtrC16 BearerName(KCDTypeNameBearerSpeed);

    TInt valueType; 

    field = (CMDBField<TUint32>*)ptrServiceRecord->GetFieldByNameL(BearerName,valueType);

    bearerSpeed = *field;

    ...

    </codeblock> </stepxmp> </substep> </substeps> </step> <step id="GUID-5B8443D8-DA79-57E6-9FC4-6A36C158090F"><cmd>Clean up. </cmd> <stepxmp><codeblock id="GUID-0E70C9AB-49B2-5ECB-9262-3A251135B5F9" xml:space="preserve">

    ...

    //

    // This also deletes "ptrSingleIAPRecord->iService.iLinkedRecord"     

    //

    delete ptrSingleIAPRecord;

    ...        

    }

}</codeblock> </stepxmp> </step> </steps> </taskbody><related-links><link href="GUID-1AFDDD6F-CB99-587D-A0B5-D3F5B27F7135.dita"><linktext>Comms Database

                concepts</linktext> </link> </related-links></task>