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category 'Scala'" aria-expanded=false type=button class="clean-btn menu__caret"></button></div><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item menu__list-item--collapsed"><div class=menu__list-item-collapsible><a class="categoryLink_byQd menu__link menu__link--sublist" tabindex=0 href=/docs/1.0.0/guide/kotlin/><span title=Kotlin class=categoryLinkLabel_W154>Kotlin</span></a><button aria-label="Expand sidebar category 'Kotlin'" aria-expanded=false type=button class="clean-btn menu__caret"></button></div><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item menu__list-item--collapsed"><div class=menu__list-item-collapsible><a class="categoryLink_byQd menu__link menu__link--sublist" tabindex=0 href=/docs/1.0.0/guide/xlang/><span title="Cross Language" class=categoryLinkLabel_W154>Cross Language</span></a><button aria-label="Expand sidebar category 'Cross Language'" aria-expanded=false type=button class="clean-btn menu__caret"></button></div></ul></ul></nav></div></div></aside><main class=docMainContainer_TBSr><div class="container padding-top--md padding-bottom--lg"><div class=row><div class="col docItemCol_VOVn"><div class="theme-doc-version-banner alert alert--warning margin-bottom--md" role=alert><div>This is documentation for <!-- -->Apache Fory™<!-- --> <b>1.0.0</b>, which is no longer actively maintained.</div><div class=margin-top--md>For up-to-date documentation, see the <b><a href=/docs/guide/dart/schema_evolution>latest version</a></b> (<!-- -->1.3.0<!-- -->).</div></div><div class=docItemContainer_Djhp><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label=Breadcrumbs><ul class=breadcrumbs><li class=breadcrumbs__item><a aria-label="Home page" class=breadcrumbs__link href=/><svg viewBox="0 0 24 24" class=breadcrumbHomeIcon_YNFT><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill=currentColor /></svg></a><li class=breadcrumbs__item><span class=breadcrumbs__link>Guide</span><li class=breadcrumbs__item><a class=breadcrumbs__link href=/docs/1.0.0/guide/dart/><span>Dart</span></a><li class="breadcrumbs__item breadcrumbs__item--active"><span class=breadcrumbs__link>Schema Evolution</span></ul></nav><span class="theme-doc-version-badge badge badge--secondary">Version: 1.0.0</span><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type=button class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Schema Evolution</h1></header><p>Schema evolution lets different versions of your app exchange messages safely — a v2 writer can produce a message that a v1 reader can still decode, and vice versa.</p>
<h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=compatible-and-schema-consistent-evolution>Compatible And Schema-Consistent Evolution<a href=#compatible-and-schema-consistent-evolution class=hash-link aria-label="Direct link to Compatible And Schema-Consistent Evolution" title="Direct link to Compatible And Schema-Consistent Evolution" translate=no></a></h2>
<h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=compatible-mode>Compatible Mode<a href=#compatible-mode class=hash-link aria-label="Direct link to Compatible Mode" title="Direct link to Compatible Mode" translate=no></a></h3>
<p>Compatible mode is the Dart default. Keep this default when services may run different versions at
the same time, for example during a rolling deployment or when clients are not updated immediately.</p>
<div class="language-dart codeBlockContainer_Ckt0 theme-code-block" style=--prism-color:#393A34;--prism-background-color:#f6f8fa><div class=codeBlockContent_QJqH><pre tabindex=0 class="prism-code language-dart codeBlock_bY9V thin-scrollbar" style=color:#393A34;background-color:#f6f8fa><code class=codeBlockLines_e6Vv><div class=token-line style=color:#393A34><span class="token keyword" style=color:#00009f>final</span><span class="token plain"> fory </span><span class="token operator" style=color:#393A34>=</span><span class="token plain"> </span><span class="token class-name">Fory</span><span class="token punctuation" style=color:#393A34>(</span><span class="token punctuation" style=color:#393A34>)</span><span class="token punctuation" style=color:#393A34>;</span><br/></div></code></pre></div></div>
<p>In compatible mode, Fory includes enough field metadata in each message so that the reader can skip unknown fields and use defaults for missing ones. Use stable field IDs (see below) to anchor the schema across changes.</p>
<h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=schema-consistent-mode>Schema-Consistent Mode<a href=#schema-consistent-mode class=hash-link aria-label="Direct link to Schema-Consistent Mode" title="Direct link to Schema-Consistent Mode" translate=no></a></h3>
<p>Both sides must have the same model. Fory validates that the schemas match and will reject messages from a different schema version. Use this when all services are always updated together and you want schema mismatches to be caught as fast errors.</p>
<div class="language-dart codeBlockContainer_Ckt0 theme-code-block" style=--prism-color:#393A34;--prism-background-color:#f6f8fa><div class=codeBlockContent_QJqH><pre tabindex=0 class="prism-code language-dart codeBlock_bY9V thin-scrollbar" style=color:#393A34;background-color:#f6f8fa><code class=codeBlockLines_e6Vv><div class=token-line style=color:#393A34><span class="token keyword" style=color:#00009f>final</span><span class="token plain"> fory </span><span class="token operator" style=color:#393A34>=</span><span class="token plain"> </span><span class="token class-name">Fory</span><span class="token punctuation" style=color:#393A34>(</span><span class="token plain">compatible</span><span class="token punctuation" style=color:#393A34>:</span><span class="token plain"> </span><span class="token boolean" style=color:#36acaa>false</span><span class="token punctuation" style=color:#393A34>)</span><span class="token punctuation" style=color:#393A34>;</span><br/></div></code></pre></div></div>
<h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=setting-up-for-evolution>Setting Up for Evolution<a href=#setting-up-for-evolution class=hash-link aria-label="Direct link to Setting Up for Evolution" title="Direct link to Setting Up for Evolution" translate=no></a></h2>
<p>To use compatible mode safely, mark your structs with <code>@ForyStruct(evolving: true)</code> (the default) and assign a stable <code>@ForyField(id: ...)</code> to every field <strong>before you ship your first payload</strong>:</p>
<div class="language-dart codeBlockContainer_Ckt0 theme-code-block" style=--prism-color:#393A34;--prism-background-color:#f6f8fa><div class=codeBlockContent_QJqH><pre tabindex=0 class="prism-code language-dart codeBlock_bY9V thin-scrollbar" style=color:#393A34;background-color:#f6f8fa><code class=codeBlockLines_e6Vv><div class=token-line style=color:#393A34><span class="token metadata function" style=color:#d73a49>@ForyStruct</span><span class="token punctuation" style=color:#393A34>(</span><span class="token plain">evolving</span><span class="token punctuation" style=color:#393A34>:</span><span class="token plain"> </span><span class="token boolean" style=color:#36acaa>true</span><span class="token punctuation" style=color:#393A34>)</span><span class="token plain"></span><br/></div><div class=token-line style=color:#393A34><span class="token plain"></span><span class="token keyword" style=color:#00009f>class</span><span class="token plain"> </span><span class="token class-name">UserProfile</span><span class="token plain"> </span><span class="token punctuation" style=color:#393A34>{</span><span class="token plain"></span><br/></div><div class=token-line style=color:#393A34><span class="token plain"> </span><span class="token class-name">UserProfile</span><span class="token punctuation" style=color:#393A34>(</span><span class="token punctuation" style=color:#393A34>)</span><span class="token punctuation" style=color:#393A34>;</span><span class="token plain"></span><br/></div><div class=token-line style=color:#393A34><span class="token plain" style=display:inline-block></span><br/></div><div class=token-line style=color:#393A34><span class="token plain"> </span><span class="token metadata function" style=color:#d73a49>@ForyField</span><span class="token punctuation" style=color:#393A34>(</span><span class="token plain">id</span><span class="token punctuation" style=color:#393A34>:</span><span class="token plain"> </span><span class="token number" style=color:#36acaa>1</span><span class="token punctuation" style=color:#393A34>)</span><span class="token plain"></span><br/></div><div class=token-line style=color:#393A34><span class="token plain"> </span><span class="token class-name">String</span><span class="token plain"> name </span><span class="token operator" style=color:#393A34>=</span><span class="token plain"> </span><span class="token string-literal string" style=color:#e3116c>''</span><span class="token punctuation" style=color:#393A34>;</span><span class="token plain"></span><br/></div><div class=token-line style=color:#393A34><span class="token plain" style=display:inline-block></span><br/></div><div class=token-line style=color:#393A34><span class="token plain"> </span><span class="token metadata function" style=color:#d73a49>@ForyField</span><span class="token punctuation" style=color:#393A34>(</span><span class="token plain">id</span><span class="token punctuation" style=color:#393A34>:</span><span class="token plain"> </span><span class="token number" style=color:#36acaa>2</span><span class="token punctuation" style=color:#393A34>,</span><span class="token plain"> nullable</span><span class="token punctuation" style=color:#393A34>:</span><span class="token plain"> </span><span class="token boolean" style=color:#36acaa>true</span><span class="token punctuation" style=color:#393A34>)</span><span class="token plain"></span><br/></div><div class=token-line style=color:#393A34><span class="token plain"> </span><span class="token class-name">String</span><span class="token operator" style=color:#393A34>?</span><span class="token plain"> nickname</span><span class="token punctuation" style=color:#393A34>;</span><span class="token plain"></span><br/></div><div class=token-line style=color:#393A34><span class="token plain"></span><span class="token punctuation" style=color:#393A34>}</span><br/></div></code></pre></div></div>
<p>If you add field IDs after payloads are already in production, existing stored messages won't have them and evolution won't work correctly.</p>
<h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=what-you-can-safely-change>What You Can Safely Change<a href=#what-you-can-safely-change class=hash-link aria-label="Direct link to What You Can Safely Change" title="Direct link to What You Can Safely Change" translate=no></a></h2>
<p><strong>Safe changes</strong> (compatible on both sides):</p>
<ul>
<li class="">Add a new optional field with a new, unused field ID.</li>
<li class="">Rename a field — as long as the <code>@ForyField(id: ...)</code> stays the same.</li>
<li class="">Remove a field — the peer will just ignore the missing value and use the Dart default.</li>
</ul>
<p><strong>Unsafe changes</strong> (may break existing messages):</p>
<ul>
<li class="">Reuse an existing field ID for a different field.</li>
<li class="">Change a field's type to an incompatible type (e.g., <code>@ForyField(type: Int32Type()) int</code><code>String</code>).</li>
<li class="">Change the registration identity (<code>id</code>, <code>namespace</code>, or <code>typeName</code>) of a type after messages are in production.</li>
<li class="">Change a field's logical meaning without changing its ID.</li>
</ul>
<h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=xlang-notes>Xlang Notes<a href=#xlang-notes class=hash-link aria-label="Direct link to Xlang Notes" title="Direct link to Xlang Notes" translate=no></a></h2>
<p>Evolution only works when <strong>all</strong> runtimes that exchange messages agree on:</p>
<ol>
<li class="">The same <code>compatible</code> setting.</li>
<li class="">The same type registration identity (numeric ID or <code>namespace + typeName</code>).</li>
<li class="">The logical meaning of field IDs.</li>
</ol>
<p>Test rolling-upgrade scenarios with real round trips before deploying.</p>
<h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=related-topics>Related Topics<a href=#related-topics class=hash-link aria-label="Direct link to Related Topics" title="Direct link to Related Topics" translate=no></a></h2>
<ul>
<li class=""><a class="" href=/docs/1.0.0/guide/dart/configuration>Configuration</a></li>
<li class=""><a class="" href=/docs/1.0.0/guide/dart/schema_metadata>Schema Metadata</a></li>
<li class=""><a class="" href=/docs/1.0.0/guide/dart/xlang_serialization>Xlang Serialization</a></li>
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