771 lines
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771 lines
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data-level="4"
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data-chapter-title="Callbacks"
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data-filepath="callbacks.md"
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data-revision="Tue Aug 16 2016 16:57:46 GMT+0800 (CST)"
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Getting Started with GORM
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<b>1.</b>
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Database
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<a href="database.html#connecting-to-a-database">
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<b>1.1.</b>
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Database Connection
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<a href="database.html#migration">
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<b>1.2.</b>
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Migration
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</a>
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<b>2.</b>
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Models
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</a>
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<ul class="articles">
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<b>2.1.</b>
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Model Definition
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<a href="models.html#conventions">
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<b>2.2.</b>
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Conventions & Overriding
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</a>
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<li class="chapter " data-level="2.3" data-path="associations.html">
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<a href="associations.html">
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<b>2.3.</b>
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Associations
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</a>
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<ul class="articles">
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<li class="chapter " data-level="2.3.1" data-path="associations.html">
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<a href="associations.html#belongs-to">
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<b>2.3.1.</b>
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Belongs To
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</a>
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</li>
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<li class="chapter " data-level="2.3.2" data-path="associations.html">
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<a href="associations.html#has-one">
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<b>2.3.2.</b>
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Has One
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</a>
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</li>
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<li class="chapter " data-level="2.3.3" data-path="associations.html">
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<a href="associations.html#has-many">
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<b>2.3.3.</b>
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Has Many
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</a>
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</li>
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<li class="chapter " data-level="2.3.4" data-path="associations.html">
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<a href="associations.html#many-to-many">
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<b>2.3.4.</b>
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Many To Many
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</a>
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</li>
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<li class="chapter " data-level="2.3.5" data-path="associations.html">
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<a href="associations.html#polymorphism">
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<b>2.3.5.</b>
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Polymorphism
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</a>
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</li>
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<li class="chapter " data-level="2.3.6" data-path="associations.html">
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<a href="associations.html#association-mode">
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<b>2.3.6.</b>
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Association Mode
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</a>
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</li>
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</ul>
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</ul>
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</li>
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<li class="chapter " data-level="3" data-path="curd.html">
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<a href="curd.html">
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<b>3.</b>
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CRUD: Reading and Writing Data
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</a>
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<ul class="articles">
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<li class="chapter " data-level="3.1" data-path="curd.html">
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<a href="curd.html#create">
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<b>3.1.</b>
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Create
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</a>
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</li>
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<li class="chapter " data-level="3.2" data-path="curd.html">
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<a href="curd.html#query">
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<b>3.2.</b>
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Query
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</a>
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</li>
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<li class="chapter " data-level="3.3" data-path="curd.html">
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<a href="curd.html#preloading-eager-loading">
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<b>3.3.</b>
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Preloading (Eager Loading)
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</a>
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</li>
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<li class="chapter " data-level="3.4" data-path="curd.html">
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<a href="curd.html#update">
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<b>3.4.</b>
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Update
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</a>
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</li>
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<li class="chapter " data-level="3.5" data-path="curd.html">
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<a href="curd.html#delete">
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<b>3.5.</b>
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Delete / Soft Delete
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter active" data-level="4" data-path="callbacks.html">
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<a href="callbacks.html">
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<b>4.</b>
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Callbacks
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</a>
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</li>
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<li class="chapter " data-level="5" data-path="advanced.html">
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<a href="advanced.html">
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<b>5.</b>
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Advanced Usage
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</a>
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<ul class="articles">
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<li class="chapter " data-level="5.1" data-path="advanced.html">
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<a href="advanced.html#error-handling">
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<b>5.1.</b>
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Error Handling
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</a>
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</li>
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<li class="chapter " data-level="5.2" data-path="advanced.html">
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<a href="advanced.html#transactions">
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<b>5.2.</b>
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Transactions
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</a>
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</li>
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<li class="chapter " data-level="5.3" data-path="advanced.html">
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<a href="advanced.html#sql-builder">
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<b>5.3.</b>
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Raw SQL & SQL Builder
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</a>
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</li>
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<li class="chapter " data-level="5.4" data-path="advanced.html">
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<a href="advanced.html#generic-database-interface-sqldb">
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<b>5.4.</b>
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Generic database interface sql.DB
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</a>
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</li>
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<li class="chapter " data-level="5.5" data-path="advanced.html">
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<a href="advanced.html#compose-primary-key">
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<b>5.5.</b>
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Composite Primary Key
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</a>
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</li>
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<li class="chapter " data-level="5.6" data-path="advanced.html">
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<a href="advanced.html#logger">
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<b>5.6.</b>
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Overriding Logger
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="6" data-path="development.html">
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<a href="development.html">
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<b>6.</b>
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Development
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</a>
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<ul class="articles">
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<li class="chapter " data-level="6.1" data-path="development.html">
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<a href="development.html#architecture">
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<b>6.1.</b>
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Architecture
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</a>
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</li>
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<li class="chapter " data-level="6.2" data-path="development.html">
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<a href="development.html#write-plugins">
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<b>6.2.</b>
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Write Plugins
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="7" data-path="changelog.html">
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<a href="changelog.html">
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<b>7.</b>
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Change Log
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</a>
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<!-- Title -->
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<h1>
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<i class="fa fa-circle-o-notch fa-spin"></i>
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<a href="." >Callbacks</a>
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</h1>
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<section class="normal markdown-section">
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<h1 id="callbacks">Callbacks</h1>
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<!-- toc -->
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<ul>
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<li><a href="#creating-an-object">Creating An Object</a></li>
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<li><a href="#updating-an-object">Updating An Object</a></li>
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<li><a href="#deleting-an-object">Deleting An Object</a></li>
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<li><a href="#querying-an-object">Querying An Object</a></li>
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<li><a href="#callback-examples">Callback Examples</a></li>
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</ul>
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<!-- toc stop -->
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<p>You could define callback methods to pointer of model struct, it will be called when creating, updating, querying, deleting, if any callback returns an error, gorm will stop future operations and rollback all changes.</p>
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<h3 id="creating-an-object">Creating An Object</h3>
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<p>Available Callbacks for creating</p>
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<pre><code class="lang-go"><span class="hljs-comment">// begin transaction</span>
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BeforeSave
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BeforeCreate
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<span class="hljs-comment">// save before associations</span>
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<span class="hljs-comment">// update timestamp `CreatedAt`, `UpdatedAt`</span>
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<span class="hljs-comment">// save self</span>
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<span class="hljs-comment">// reload fields that have default value and its value is blank</span>
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<span class="hljs-comment">// save after associations</span>
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AfterCreate
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AfterSave
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<span class="hljs-comment">// commit or rollback transaction</span>
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</code></pre>
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<h3 id="updating-an-object">Updating An Object</h3>
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<p>Available Callbacks for updating</p>
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<pre><code class="lang-go"><span class="hljs-comment">// begin transaction</span>
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BeforeSave
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BeforeUpdate
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<span class="hljs-comment">// save before associations</span>
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<span class="hljs-comment">// update timestamp `UpdatedAt`</span>
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<span class="hljs-comment">// save self</span>
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<span class="hljs-comment">// save after associations</span>
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AfterUpdate
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AfterSave
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<span class="hljs-comment">// commit or rollback transaction</span>
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</code></pre>
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<h3 id="deleting-an-object">Deleting An Object</h3>
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<p>Available Callbacks for deleting</p>
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<pre><code class="lang-go"><span class="hljs-comment">// begin transaction</span>
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BeforeDelete
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<span class="hljs-comment">// delete self</span>
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AfterDelete
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<span class="hljs-comment">// commit or rollback transaction</span>
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</code></pre>
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<h3 id="querying-an-object">Querying An Object</h3>
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<p>Available Callbacks for querying</p>
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<pre><code class="lang-go"><span class="hljs-comment">// load data from database</span>
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<span class="hljs-comment">// Preloading (edger loading)</span>
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AfterFind
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</code></pre>
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<h3 id="callback-examples">Callback Examples</h3>
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<pre><code class="lang-go"><span class="hljs-keyword">func</span> (u *User) BeforeUpdate() (err error) {
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<span class="hljs-keyword">if</span> u.readonly() {
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err = errors.New(<span class="hljs-string">"read only user"</span>)
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}
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<span class="hljs-keyword">return</span>
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}
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<span class="hljs-comment">// Rollback the insertion if user's id greater than 1000</span>
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<span class="hljs-keyword">func</span> (u *User) AfterCreate() (err error) {
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<span class="hljs-keyword">if</span> (u.Id > <span class="hljs-number">1000</span>) {
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err = errors.New(<span class="hljs-string">"user id is already greater than 1000"</span>)
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}
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<span class="hljs-keyword">return</span>
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}
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</code></pre>
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<p>Save/Delete operations in gorm are running in transactions, so changes made in that transaction are not visible unless it is commited.
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If you want to use those changes in your callbacks, you need to run your SQL in the same transaction. So you need to pass current transaction to callbacks like this:</p>
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<pre><code class="lang-go"><span class="hljs-keyword">func</span> (u *User) AfterCreate(tx *gorm.DB) (err error) {
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tx.Model(u).Update(<span class="hljs-string">"role"</span>, <span class="hljs-string">"admin"</span>)
|
|
<span class="hljs-keyword">return</span>
|
|
}
|
|
</code></pre>
|
|
<pre><code class="lang-go"><span class="hljs-keyword">func</span> (u *User) AfterCreate(scope *gorm.Scope) (err error) {
|
|
scope.DB().Model(u).Update(<span class="hljs-string">"role"</span>, <span class="hljs-string">"admin"</span>)
|
|
<span class="hljs-keyword">return</span>
|
|
}
|
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</code></pre>
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