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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 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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<li class="chapter " data-level="2.3.4" data-path="associations.html">
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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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<a href="curd.html#query">
<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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<li class="chapter " data-level="5.1" data-path="advanced.html">
<a href="advanced.html#error-handling">
<b>5.1.</b>
Error Handling
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<b>5.2.</b>
Transactions
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<a href="advanced.html#sql-builder">
<b>5.3.</b>
Raw SQL &amp; SQL Builder
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<a href="advanced.html#generic-database-interface-sqldb">
<b>5.4.</b>
Generic database interface sql.DB
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<li class="chapter " data-level="5.5" data-path="advanced.html">
<a href="advanced.html#compose-primary-key">
<b>5.5.</b>
Composite Primary Key
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<a href="advanced.html#logger">
<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="advanced-usage">Advanced Usage</h1>
<!-- toc -->
<ul>
<li><a href="#error-handling">Error Handling</a></li>
<li><a href="#transactions">Transactions</a><ul>
<li><a href="#a-specific-example">A Specific Example</a></li>
</ul>
</li>
<li><a href="#sql-builder">SQL Builder</a><ul>
<li><a href="#run-raw-sql">Run Raw SQL</a></li>
<li><a href="#sqlrow-sqlrows">sql.Row &amp; sql.Rows</a></li>
<li><a href="#scan-sqlrows-in-iteration">Scan sql.Rows In Iteration</a></li>
</ul>
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<li><a href="#generic-database-interface-sqldb">Generic database interface sql.DB</a><ul>
<li><a href="#connection-pool">Connection Pool</a></li>
</ul>
</li>
<li><a href="#composite-primary-key">Composite Primary Key</a></li>
<li><a href="#logger">Logger</a><ul>
<li><a href="#customize-logger">Customize Logger</a></li>
</ul>
</li>
</ul>
<!-- toc stop -->
<h2 id="error-handling">Error Handling</h2>
<p>After perform any operations, if there are any error happened, GORM will set it to <code>*DB</code>&apos;s <code>Error</code> field</p>
<pre><code class="lang-go"><span class="hljs-keyword">if</span> err := db.Where(<span class="hljs-string">&quot;name = ?&quot;</span>, <span class="hljs-string">&quot;jinzhu&quot;</span>).First(&amp;user).Error; err != <span class="hljs-literal">nil</span> {
<span class="hljs-comment">// error handling...</span>
}
<span class="hljs-comment">// If there are more than one error happened, get all of them with `GetErrors`, it returns `[]error`</span>
db.First(&amp;user).Limit(<span class="hljs-number">10</span>).Find(&amp;users).GetErrors()
<span class="hljs-comment">// Check if returns RecordNotFound error</span>
db.Where(<span class="hljs-string">&quot;name = ?&quot;</span>, <span class="hljs-string">&quot;hello world&quot;</span>).First(&amp;user).RecordNotFound()
<span class="hljs-keyword">if</span> db.Model(&amp;user).Related(&amp;credit_card).RecordNotFound() {
<span class="hljs-comment">// no credit card found handling</span>
}
</code></pre>
<h2 id="transactions">Transactions</h2>
<p>To perform a set of operations within a transaction, the general flow is as below.</p>
<pre><code class="lang-go"><span class="hljs-comment">// begin a transaction</span>
tx := db.Begin()
<span class="hljs-comment">// do some database operations in the transaction (use &apos;tx&apos; from this point, not &apos;db&apos;)</span>
tx.Create(...)
<span class="hljs-comment">// ...</span>
<span class="hljs-comment">// rollback the transaction in case of error</span>
tx.Rollback()
<span class="hljs-comment">// Or commit the transaction</span>
tx.Commit()
</code></pre>
<h3 id="a-specific-example">A Specific Example</h3>
<pre><code class="lang-go"><span class="hljs-keyword">func</span> CreateAnimals(db *gorm.DB) err {
tx := db.Begin()
<span class="hljs-comment">// Note the use of tx as the database handle once you are within a transaction</span>
<span class="hljs-keyword">if</span> err := tx.Create(&amp;Animal{Name: <span class="hljs-string">&quot;Giraffe&quot;</span>}).Error; err != <span class="hljs-literal">nil</span> {
tx.Rollback()
<span class="hljs-keyword">return</span> err
}
<span class="hljs-keyword">if</span> err := tx.Create(&amp;Animal{Name: <span class="hljs-string">&quot;Lion&quot;</span>}).Error; err != <span class="hljs-literal">nil</span> {
tx.Rollback()
<span class="hljs-keyword">return</span> err
}
tx.Commit()
<span class="hljs-keyword">return</span> <span class="hljs-literal">nil</span>
}
</code></pre>
<h2 id="sql-builder">SQL Builder</h2>
<h4 id="run-raw-sql">Run Raw SQL</h4>
<p>Run Raw SQL</p>
<pre><code class="lang-go">db.Exec(<span class="hljs-string">&quot;DROP TABLE users;&quot;</span>)
db.Exec(<span class="hljs-string">&quot;UPDATE orders SET shipped_at=? WHERE id IN (?)&quot;</span>, time.Now, []<span class="hljs-keyword">int64</span>{<span class="hljs-number">11</span>,<span class="hljs-number">22</span>,<span class="hljs-number">33</span>})
<span class="hljs-comment">// Scan</span>
<span class="hljs-keyword">type</span> Result <span class="hljs-keyword">struct</span> {
Name <span class="hljs-keyword">string</span>
Age <span class="hljs-keyword">int</span>
}
<span class="hljs-keyword">var</span> result Result
db.Raw(<span class="hljs-string">&quot;SELECT name, age FROM users WHERE name = ?&quot;</span>, <span class="hljs-number">3</span>).Scan(&amp;result)
</code></pre>
<h4 id="sqlrow--sqlrows">sql.Row &amp; sql.Rows</h4>
<p>Get query result as <code>*sql.Row</code> or <code>*sql.Rows</code></p>
<pre><code class="lang-go">row := db.Table(<span class="hljs-string">&quot;users&quot;</span>).Where(<span class="hljs-string">&quot;name = ?&quot;</span>, <span class="hljs-string">&quot;jinzhu&quot;</span>).Select(<span class="hljs-string">&quot;name, age&quot;</span>).Row() <span class="hljs-comment">// (*sql.Row)</span>
row.Scan(&amp;name, &amp;age)
rows, err := db.Model(&amp;User{}).Where(<span class="hljs-string">&quot;name = ?&quot;</span>, <span class="hljs-string">&quot;jinzhu&quot;</span>).Select(<span class="hljs-string">&quot;name, age, email&quot;</span>).Rows() <span class="hljs-comment">// (*sql.Rows, error)</span>
<span class="hljs-keyword">defer</span> rows.Close()
<span class="hljs-keyword">for</span> rows.Next() {
...
rows.Scan(&amp;name, &amp;age, &amp;email)
...
}
<span class="hljs-comment">// Raw SQL</span>
rows, err := db.Raw(<span class="hljs-string">&quot;select name, age, email from users where name = ?&quot;</span>, <span class="hljs-string">&quot;jinzhu&quot;</span>).Rows() <span class="hljs-comment">// (*sql.Rows, error)</span>
<span class="hljs-keyword">defer</span> rows.Close()
<span class="hljs-keyword">for</span> rows.Next() {
...
rows.Scan(&amp;name, &amp;age, &amp;email)
...
}
</code></pre>
<h4 id="scan-sqlrows-in-iteration">Scan sql.Rows In Iteration</h4>
<pre><code class="lang-go">rows, err := db.Model(&amp;User{}).Where(<span class="hljs-string">&quot;name = ?&quot;</span>, <span class="hljs-string">&quot;jinzhu&quot;</span>).Select(<span class="hljs-string">&quot;name, age, email&quot;</span>).Rows() <span class="hljs-comment">// (*sql.Rows, error)</span>
<span class="hljs-keyword">defer</span> rows.Close()
<span class="hljs-keyword">for</span> rows.Next() {
<span class="hljs-keyword">var</span> user User
db.ScanRows(rows, &amp;user)
<span class="hljs-comment">// do something</span>
}
</code></pre>
<h2 id="generic-database-interface-sqldb">Generic database interface sql.DB</h2>
<p>Get generic database interface <a href="http://golang.org/pkg/database/sql/#DB" target="_blank">*sql.DB</a> from <code>*gorm.DB</code> connection</p>
<pre><code class="lang-go"><span class="hljs-comment">// Get generic database object `*sql.DB` to use its functions</span>
db.DB()
<span class="hljs-comment">// Ping</span>
db.DB().Ping()
</code></pre>
<h4 id="connection-pool">Connection Pool</h4>
<pre><code class="lang-go">db.DB().SetMaxIdleConns(<span class="hljs-number">10</span>)
db.DB().SetMaxOpenConns(<span class="hljs-number">100</span>)
</code></pre>
<h2 id="composite-primary-key">Composite Primary Key</h2>
<p>Set multiple fields as priamry key to enable composite primary key</p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Product <span class="hljs-keyword">struct</span> {
ID <span class="hljs-keyword">string</span> <span class="hljs-string">`gorm:&quot;primary_key&quot;`</span>
LanguageCode <span class="hljs-keyword">string</span> <span class="hljs-string">`gorm:&quot;primary_key&quot;`</span>
}
</code></pre>
<h2 id="logger">Logger</h2>
<p>Gorm has built-in logger support, by default, it will print happened errors</p>
<pre><code class="lang-go"><span class="hljs-comment">// Enable Logger, show detailed log</span>
db.LogMode(<span class="hljs-literal">true</span>)
<span class="hljs-comment">// Diable Logger, don&apos;t show any log</span>
db.LogMode(<span class="hljs-literal">false</span>)
<span class="hljs-comment">// Debug a single operation, show detailed log for this operation</span>
db.Debug().Where(<span class="hljs-string">&quot;name = ?&quot;</span>, <span class="hljs-string">&quot;jinzhu&quot;</span>).First(&amp;User{})
</code></pre>
<h4 id="customize-logger">Customize Logger</h4>
<p>Refer GORM&apos;s default logger for how to customize it <a href="https://github.com/jinzhu/gorm/blob/master/logger.go" target="_blank">https://github.com/jinzhu/gorm/blob/master/logger.go</a></p>
<pre><code class="lang-go">db.SetLogger(gorm.Logger{revel.TRACE})
db.SetLogger(log.New(os.Stdout, <span class="hljs-string">&quot;\r\n&quot;</span>, <span class="hljs-number">0</span>))
</code></pre>
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