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Getting Started with GORM
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<b>1.</b>
Database
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<b>1.1.</b>
Database Connection
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<b>1.2.</b>
Migration
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<b>2.</b>
Models
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<b>2.1.</b>
Model Definition
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<b>2.2.</b>
Conventions &amp; Overriding
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<b>2.3.</b>
Associations
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<b>2.3.1.</b>
Belongs To
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<b>2.3.2.</b>
Has One
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<b>2.3.3.</b>
Has Many
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<b>2.3.4.</b>
Many To Many
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<b>2.3.5.</b>
Polymorphism
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<b>2.3.6.</b>
Association Mode
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<b>3.</b>
CRUD: Reading and Writing Data
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<li class="chapter " data-level="3.1" data-path="curd.html">
<a href="curd.html#create">
<b>3.1.</b>
Create
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<b>3.2.</b>
Query
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<b>3.3.</b>
Preloading (Eager Loading)
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<b>3.4.</b>
Update
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<b>3.5.</b>
Delete / Soft Delete
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<b>4.</b>
Callbacks
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<b>5.</b>
Advanced Usage
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<b>5.1.</b>
Error Handling
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<b>5.2.</b>
Transactions
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<b>5.3.</b>
Raw SQL &amp; SQL Builder
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<b>5.4.</b>
Generic database interface sql.DB
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<b>5.5.</b>
Composite Primary Key
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<b>5.6.</b>
Overriding Logger
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Development
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<b>6.1.</b>
Architecture
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<b>6.2.</b>
Write Plugins
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Change Log
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<h1 id="development">Development</h1>
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<ul>
<li><a href="#architecture">Architecture</a></li>
<li><a href="#write-plugins">Write Plugins</a><ul>
<li><a href="#register-a-new-callback">Register a new callback</a></li>
<li><a href="#delete-an-existing-callback">Delete an existing callback</a></li>
<li><a href="#replace-an-existing-callback">Replace an existing callback</a></li>
<li><a href="#register-callback-orders">Register callback orders</a></li>
<li><a href="#pre-defined-callbacks">Pre-Defined Callbacks</a></li>
</ul>
</li>
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<!-- toc stop -->
<h2 id="architecture">Architecture</h2>
<p>Gorm use chainable API, <code>*gorm.DB</code> is the bridge of chains, for each chain API, it will create a new relation.</p>
<pre><code class="lang-go">db, err := gorm.Open(<span class="hljs-string">&quot;postgres&quot;</span>, <span class="hljs-string">&quot;user=gorm dbname=gorm sslmode=disable&quot;</span>)
<span class="hljs-comment">// create a new relation</span>
db = db.Where(<span class="hljs-string">&quot;name = ?&quot;</span>, <span class="hljs-string">&quot;jinzhu&quot;</span>)
<span class="hljs-comment">// filter even more</span>
<span class="hljs-keyword">if</span> SomeCondition {
db = db.Where(<span class="hljs-string">&quot;age = ?&quot;</span>, <span class="hljs-number">20</span>)
} <span class="hljs-keyword">else</span> {
db = db.Where(<span class="hljs-string">&quot;age = ?&quot;</span>, <span class="hljs-number">30</span>)
}
<span class="hljs-keyword">if</span> YetAnotherCondition {
db = db.Where(<span class="hljs-string">&quot;active = ?&quot;</span>, <span class="hljs-number">1</span>)
}
</code></pre>
<p>When we start to perform any operations, GROM will create a new <code>*gorm.Scope</code> instance based on current <code>*gorm.DB</code></p>
<pre><code class="lang-go"><span class="hljs-comment">// perform a querying operation</span>
db.First(&amp;user)
</code></pre>
<p>And based on current operation&apos;s type, it will call registered <code>creating</code>, <code>updating</code>, <code>querying</code>, <code>deleting</code> or <code>row_querying</code> callbacks to run the operation.</p>
<p>For above example, will call <code>querying</code> callbacks, refer <a href="callbacks.html#querying-an-object">Querying Callbacks</a></p>
<h2 id="write-plugins">Write Plugins</h2>
<p>GORM itself is powered by <code>Callbacks</code>, so you could fully customize GORM as you want</p>
<h3 id="register-a-new-callback">Register a new callback</h3>
<pre><code>func updateCreated(scope *Scope) {
if scope.HasColumn(&quot;Created&quot;) {
scope.SetColumn(&quot;Created&quot;, NowFunc())
}
}
db.Callback().Create().Register(&quot;update_created_at&quot;, updateCreated)
// register a callback for Create process
</code></pre><h3 id="delete-an-existing-callback">Delete an existing callback</h3>
<pre><code>db.Callback().Create().Remove(&quot;gorm:create&quot;)
// delete callback `gorm:create` from Create callbacks
</code></pre><h3 id="replace-an-existing-callback">Replace an existing callback</h3>
<pre><code>db.Callback().Create().Replace(&quot;gorm:create&quot;, newCreateFunction)
// replace callback `gorm:create` with new function `newCreateFunction` for Create process
</code></pre><h3 id="register-callback-orders">Register callback orders</h3>
<pre><code>db.Callback().Create().Before(&quot;gorm:create&quot;).Register(&quot;update_created_at&quot;, updateCreated)
db.Callback().Create().After(&quot;gorm:create&quot;).Register(&quot;update_created_at&quot;, updateCreated)
db.Callback().Query().After(&quot;gorm:query&quot;).Register(&quot;my_plugin:after_query&quot;, afterQuery)
db.Callback().Delete().After(&quot;gorm:delete&quot;).Register(&quot;my_plugin:after_delete&quot;, afterDelete)
db.Callback().Update().Before(&quot;gorm:update&quot;).Register(&quot;my_plugin:before_update&quot;, beforeUpdate)
db.Callback().Create().Before(&quot;gorm:create&quot;).After(&quot;gorm:before_create&quot;).Register(&quot;my_plugin:before_create&quot;, beforeCreate)
</code></pre><h3 id="predefined-callbacks">Pre-Defined Callbacks</h3>
<p>GORM has defiend callbacks to perform its CRUD operations, check them out before start write your plugins</p>
<ul>
<li><p><a href="https://github.com/jinzhu/gorm/blob/master/callback_create.go" target="_blank">Create callbacks</a></p>
</li>
<li><p><a href="https://github.com/jinzhu/gorm/blob/master/callback_update.go" target="_blank">Update callbacks</a></p>
</li>
<li><p><a href="https://github.com/jinzhu/gorm/blob/master/callback_query.go" target="_blank">Query callbacks</a></p>
</li>
<li><p><a href="https://github.com/jinzhu/gorm/blob/master/callback_delete.go" target="_blank">Delete callbacks</a></p>
</li>
<li><p>Row Query callbacks</p>
</li>
</ul>
<p>Row Query callbacks will be called when run <code>Row</code> or <code>Rows</code>, by default there is no registered callbacks for it, you could register a new one like:</p>
<pre><code class="lang-go"><span class="hljs-keyword">func</span> updateTableName(scope *gorm.Scope) {
scope.Search.Table(scope.TableName() + <span class="hljs-string">&quot;_draft&quot;</span>) <span class="hljs-comment">// append `_draft` to table name</span>
}
db.Callback().RowQuery().Register(<span class="hljs-string">&quot;publish:update_table_name&quot;</span>, updateTableName)
</code></pre>
<p>View <a href="https://godoc.org/github.com/jinzhu/gorm" target="_blank">https://godoc.org/github.com/jinzhu/gorm</a> to view all available API</p>
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