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Getting Started with GORM
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<b>1.</b>
Database
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<li class="chapter " data-level="1.1" data-path="database.html">
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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 Defination
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<b>2.2.</b>
Naming 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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<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>
Composite Primary Key
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<b>5.5.</b>
Overriding Logger
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<b>6.</b>
Development
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<b>6.1.</b>
Write Plugins
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<h1 id="gorm-development">Gorm Development</h1>
<!-- toc -->
<ul>
<li><a href="#architecture">Architecture</a></li>
<li><a href="#callbacks">Callbacks</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="#callback-api">Callback API</a></li>
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<h2 id="architecture">Architecture</h2>
<p>The most notable component of Gorm is<code>gorm.DB</code>, which hold database connection. It could be initialized like this:</p>
<pre><code>db, err := gorm.Open(&quot;postgres&quot;, &quot;user=gorm dbname=gorm sslmode=disable&quot;)
</code></pre><p>Gorm has chainable API, <code>gorm.DB</code> is the bridge of chains, it save related information and pass it to the next chain.</p>
<p>Lets use below code to explain how it works:</p>
<pre><code>db.Where(&quot;name = ?&quot;, &quot;jinzhu&quot;).Find(&amp;users)
// equivalent code
newdb := db.Where(&quot;name =?&quot;, &quot;jinzhu&quot;)
newdb.Find(&amp;user)
</code></pre><p><code>newdb</code> is <code>db</code>&apos;s clone, in addition, it contains search conditions from the <code>Where</code> method.
<code>Find</code> is a query method, it creates a <code>Scope</code> instance, and pass it as argument to query callbacks.</p>
<p>There are four kinds of callbacks corresponds to sql&apos;s CURD: create callbacks, update callbacks, query callbacks, delete callbacks.</p>
<h2 id="callbacks">Callbacks</h2>
<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="callback-api">Callback API</h3>
<p>Gorm is powered by callbacks, so you could refer below links to learn how to write callbacks</p>
<p><a href="https://github.com/jinzhu/gorm/blob/master/callback_create.go" target="_blank">Create callbacks</a></p>
<p><a href="https://github.com/jinzhu/gorm/blob/master/callback_update.go" target="_blank">Update callbacks</a></p>
<p><a href="https://github.com/jinzhu/gorm/blob/master/callback_query.go" target="_blank">Query callbacks</a></p>
<p><a href="https://github.com/jinzhu/gorm/blob/master/callback_delete.go" target="_blank">Delete callbacks</a></p>
<p>View <a href="https://github.com/jinzhu/gorm/blob/master/scope.go" target="_blank">https://github.com/jinzhu/gorm/blob/master/scope.go</a> for all available API</p>
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