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<concept id="GUID-36718217-C9F7-5ACF-8DE7-7D83FBF435DB" xml:lang="en"><title>Store

map cleanup support</title><shortdesc>This document describes store map cleanup support.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The destructor of a <codeph>CStoreMap</codeph> object calls the <codeph>ResetAndDestroy()</codeph> member

function. This function deletes from the store all streams whose stream IDs

are currently held by the store map.</p>

<p>This is of most use:</p>

<ul>

<li id="GUID-1978575F-24D5-5B3A-8FED-5A067ACF5691"><p>in stores which do not

support commit and revert, for example, the non-persistent in-memory store <codeph>CBufStore</codeph>.</p> </li>

<li id="GUID-C8FBA74B-939B-576B-9443-D55AD9B798EC"><p>where the streams, whose

IDs are in the store map, do not contain pointers to other streams.</p> </li>

</ul>

<p>This behaviour allows a partially complete set of streams to be deleted

if a leave occurs part of the way through the building of the set.</p>

<p>Note that this behaviour cannot be exploited by stores which do not support

the deletion of streams, for example, the direct file store <codeph>CDirectFileStore</codeph>.</p>

<p>Stores such as the permanent file store, <codeph>CPermanentFileStore</codeph>,

can also use commit and revert to implement this kind of behaviour.</p>

<p>Given the example class, <codeph>CCompound</codeph>, defined as:</p>

<codeblock id="GUID-84E229C8-624C-5024-B25B-DB5957580775" xml:space="preserve">class CCompound : public CBase

    {

    ...

    TSwizzle<CClassA> iA;

    TSwizzle<CClassB> iB;

    TSwizzle<CClassC> iC; 

    ...

    }</codeblock>

<p>the <codeph>CCompound</codeph> object is stored using its <codeph>StoreL()</codeph> function

and the individual components are externalised by the <codeph>StoreComponentsL()</codeph> function:</p>

<codeblock id="GUID-10BD78DC-C674-5C28-BECE-685A51324956" xml:space="preserve">TStreamId CCompound::StoreL(CStreamStore&amp; aStore)

    {

    CStoreMap* map=CStoreMap::NewLC(aStore);

    StoreComponentsL(*map);

       RStoreWriteStream stream(*map);

    TStreamId id=stream.CreateLC(aStore);

    ExternalizeL(stream);

    stream.CommitL();

    map->Reset();

    CleanupStack::PopAndDestroy(2);

    return id;

    }</codeblock>

<codeblock id="GUID-8D249B61-5858-500D-A1A2-4C17FF9D0D63" xml:space="preserve">void CCompound::StoreComponentsL(CStoreMap&amp; aMap) const

    {

    TStreamId id;

    ...

    id = iA->StoreL(iStore);

    aMap.BindL(iA,id);

    ...

    id = iB->StoreL(iStore);

    aMap.BindL(iB,id);

    ...

    id = iC->StoreL(iStore);

    aMap.BindL(iC,id);

    ...

    }</codeblock>

<p>Once the store map has been created, a cleanup item for it is placed onto

the cleanupstack. This means that if, for example, the call to either:</p>

<codeblock id="GUID-14BA383C-B2C5-5881-97E8-FD1196B8A459" xml:space="preserve">id = iC-&gt;StoreL(iStore);</codeblock>

<p>or</p>

<codeblock id="GUID-CFE924DF-2131-51D5-A3B6-DAC756B996CA" xml:space="preserve">aMap.BindL(iC,id);</codeblock>

<p>were to fail, then the streams containing the <codeph>CClassA</codeph> and <codeph>CClassB</codeph> objects

would be deleted from the store as part of the subsequent destruction of the

store map.</p>

<p>Once all three components have been successfully externalised and the <codeph>CCompound</codeph>'s

other data has also been externalised to its own stream, and no further failure

modes are possible, then the store map can be and must be reset, by calling

its <codeph>Reset()</codeph> function.</p>

<section id="GUID-ECDB6AB8-52D0-461F-A3AB-0DA42BEB26B3"><title>See also</title> <p><xref href="GUID-C9D8D913-C65F-5A69-A606-30F59BFB38E2.dita">File

stores</xref> </p> <p><xref href="GUID-6EE0CB66-A759-5E0C-884D-90895F35F267.dita">Transactions</xref> </p> </section>

</conbody></concept>