<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
<!-- This component and the accompanying materials are made available under the terms of the License 
"Eclipse Public License v1.0" which accompanies this distribution, 
and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
<!-- Initial Contributors:
    Nokia Corporation - initial contribution.
Contributors: 
-->
<!DOCTYPE task
  PUBLIC "-//OASIS//DTD DITA Task//EN" "task.dtd">
<task id="GUID-E4874B22-474B-56D0-8A8A-C60411D3CBCB" xml:lang="en"><title>Accessing
a field without loading a whole record: Tutorial</title><shortdesc>This tutorial shows you how to access a field without loading a
whole record. </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody>


<prereq id="GUID-A02C353C-3AB5-58E1-B433-98E7158CB5CD"><p>Before you start,
you must understand: </p> <ul>
<li id="GUID-B77D629D-4E6D-5D2D-840A-0CFA5658D151"><p>the general concept
of the Comms Database </p> </li>
<li id="GUID-FAF6F934-8AF3-5500-9E25-A650B69E84F4"><p>the specific concept
of fields, records, links and tables </p> </li>
<li id="GUID-24F0BEF0-ADBB-531D-BE9B-6325E07862F2"><p>how to write and build
application code to run on Symbian platform </p> </li>
</ul> </prereq>
<context id="GUID-D907BA51-0528-5018-9B46-67AE5824CEF7"><p>This tutorial shows
you how to get the value of a field in the <xref href="GUID-387A8240-0765-52F2-98A4-8F9FC809E03E.dita#GUID-387A8240-0765-52F2-98A4-8F9FC809E03E/GUID-7383902B-10D2-52F3-8BDB-478CA6FB587D">GlobalSettings</xref> table. Records from the <codeph>GlobalSettings</codeph> table are not loaded. </p> <p>This
tutorial uses the <codeph>BearerAvailablityCheckTSY</codeph> field. This field
contains the name of the TSY used to check for bearer availability. </p> </context>
<steps id="GUID-A7B63B0B-CF57-5E84-BB08-C957C24675F9">
<step id="GUID-E0321D17-9CC5-5BF3-87A8-4A1638069214"><cmd>Make sure that you
have created a session. </cmd>
</step>
<step id="GUID-CE91627F-547F-58C0-A940-9B5461B33536"><cmd>Create the field
object in the tool or application process. </cmd>

<info>You construct a <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CMDBField</apiname></xref> <codeph>&lt;T&gt;</codeph> object
and pass <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>KCDTIdBearerAvailabilityCheckTSY</apiname></xref> to
the constructor. The symbol <codeph>KCDTIdBearerAvailabilityCheckTSY</codeph> defines
the unique numeric Id for the <codeph>BearerAvailablityCheckTSY</codeph> field. </info>
<stepxmp><codeblock id="GUID-EB189214-1590-5EB7-8233-B8C50ADCF075" xml:space="preserve">...

// Create the field object. The template parameter is TDesc, because the field value
// is a short text description. 
// Use the "... new(Eleave).. " construction to create the field object.
// Pass KCDTIdBearerAvailabilityCheckTSY as a parameter to the constructor.

CMDBField&lt;TDesC&gt;* descField = new(ELeave) CMDBField&lt;TDesC&gt;(KCDTIdBearerAvailabilityCheckTSY);
...
             </codeblock> </stepxmp>
</step>
<step id="GUID-8B20473F-C8B6-5547-907E-23F42BE260BB"><cmd>Set the data that
identifies the field and load the field </cmd>

<info>A descriptor field needs an additional call to set the size of the descriptor.
Call <codeph>SetMaxLengthL()</codeph> to set the size of the descriptor. This
function is a member of the field class <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CMDBField</apiname></xref> <codeph>&lt;TDesC&gt;</codeph>.
Internally, the function causes the allocation of a descriptor. You must set
the size of the descriptor before you assign the data. You can also use the <codeph>SetL()</codeph> function.
This function sets the length and assigns the data. The function is a member
of the field class <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CMDBField</apiname></xref> <codeph>&lt;TDesC&gt;</codeph>. </info>
<stepxmp><codeblock id="GUID-95ED9858-3123-56BE-B820-E5EE25A16FB2" xml:space="preserve">...

// The symbol "KMaxTextLength" defines the maximum length of short text.
// The record Id is ALWAYS 1 for global settings table.
descField-&gt;SetMaxLengthL(KMaxTextLength);
descField-&gt;SetRecordId(1); //recorded is ALWAYS 1 for global settings table

// Load the field.
descField-&gt;LoadL(*iDb);
...</codeblock> </stepxmp>
</step>
<step id="GUID-D6A6EA77-B3A3-5614-9129-481E2EAB30D2"><cmd>Check that the field
has a value before you use it </cmd>
<stepxmp><codeblock id="GUID-1F8C21E5-D9E1-5F1B-B695-6A143C80751D" xml:space="preserve">...
// Use the IsNull() function to check that the field has a value.
// In this example, the code leaves if the field does not have a value.
// Your code needs to handle a Null value appropriately.

if(descField-&gt;IsNull())
    {
    User::Leave(KErrNotFound);
    }
else
    {
    // Either process the content of *descField in place,
    // or copy the content to another descriptor. 
    // The processing depends on the structure of your code.
    // In this example, the content is copied into an RBuf for
    // further processing.
    RBuf buf;
    buf.CleanupClosePushL(); 
    buf.CreateL(descField);
    ...
    // Do something with the data.
    ...
    // Delete the RBuf buffer
    CleanupStack::PopAndDestroy()   
    ...
    }

// Do not forget to delete the field object.
delete descField;
...</codeblock> </stepxmp>
</step>
</steps>
</taskbody></task>