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Naming Conventions & Overriding
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Associations
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<b>2.3.1.</b>
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Belongs To
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<b>2.3.2.</b>
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Has One
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<b>2.3.3.</b>
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Has Many
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<b>2.3.4.</b>
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Many To Many
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<b>2.3.5.</b>
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Polymorphism
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<b>2.3.6.</b>
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Association Mode
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<b>3.</b>
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CRUD: Reading and Writing Data
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Create
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<b>3.2.</b>
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Query
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Preloading (Eager Loading)
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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 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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<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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<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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<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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<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#compose-primary-key">
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<b>5.4.</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="5.5" data-path="advanced.html">
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<a href="advanced.html#logger">
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<b>5.5.</b>
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Overriding Logger
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</a>
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</ul>
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Development
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<li class="chapter " data-level="6.1" data-path="development.html">
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<a href="development.html#callbacks">
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<b>6.1.</b>
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Write Plugins
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</a>
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Change Log
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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="#destroying-an-object">Destroying An Object</a></li>
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<li><a href="#after-find">After Find</a></li>
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<li><a href="#example">Example</a></li>
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</ul>
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<!-- toc stop -->
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<p>Callbacks are methods defined on the pointer of struct.
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If any callback returns an error, gorm will stop future operations and rollback all changes.</p>
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<p>Here is the list of all available callbacks:
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(listed in the same order in which they will get called during the respective operations)</p>
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<h3 id="creating-an-object">Creating An Object</h3>
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<pre><code class="lang-go">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">// save self</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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</code></pre>
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<h3 id="updating-an-object">Updating An Object</h3>
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<pre><code class="lang-go">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">// 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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</code></pre>
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<h3 id="destroying-an-object">Destroying An Object</h3>
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<pre><code class="lang-go">BeforeDelete
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<span class="hljs-comment">// delete self</span>
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AfterDelete
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</code></pre>
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<h3 id="after-find">After Find</h3>
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<pre><code class="lang-go"><span class="hljs-comment">// load data from database</span>
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AfterFind
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</code></pre>
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<h3 id="example">Example</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 a transaction.
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Changes made in that transaction are not visible unless it is commited.
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So if you want to use those changes in your callbacks, you need to run your SQL in the same transaction.
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For this Gorm supports passing transactions 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>)
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<span class="hljs-keyword">return</span>
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}
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</code></pre>
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