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Associations
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Belongs To
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Polymorphism
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<b>1.3.3.6.</b>
Association Mode
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Delete / Soft Delete
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<b>1.4.6.</b>
Associations
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Callbacks
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Advanced Usage
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Error Handling
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Transactions
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Composite Primary Key
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<h1 id="associations">Associations</h1>
<!-- toc -->
<h2 id="belongs-to">Belongs To</h2>
<pre><code class="lang-go"><span class="hljs-comment">// `User` belongs to `Profile`, `ProfileID` is the foreign key</span>
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Profile Profile
ProfileID <span class="hljs-keyword">int</span>
}
<span class="hljs-keyword">type</span> Profile <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
}
db.Model(&amp;user).Related(&amp;profile)
<span class="hljs-comment">//// SELECT * FROM profiles WHERE id = 111; // 111 is user&apos;s foreign key ProfileID</span>
</code></pre>
<p><em>Specify Foreign Key</em></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Profile <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
}
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Profile Profile <span class="hljs-string">`gorm:&quot;ForeignKey:ProfileRefer&quot;`</span> <span class="hljs-comment">// use ProfileRefer as foreign key</span>
ProfileRefer <span class="hljs-keyword">uint</span>
}
</code></pre>
<p><em>Specify Foreign Key &amp; Association Key</em></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Profile <span class="hljs-keyword">struct</span> {
gorm.Model
Refer <span class="hljs-keyword">int</span>
Name <span class="hljs-keyword">string</span>
}
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Profile Profile <span class="hljs-string">`gorm:&quot;ForeignKey:ProfileID;AssociationForeignKey:Refer&quot;`</span>
ProfileID <span class="hljs-keyword">int</span>
}
</code></pre>
<h2 id="has-one">Has One</h2>
<pre><code class="lang-go"><span class="hljs-comment">// User has one CreditCard, UserID is the foreign key</span>
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
CreditCard CreditCard
}
<span class="hljs-keyword">type</span> CreditCard <span class="hljs-keyword">struct</span> {
gorm.Model
UserID <span class="hljs-keyword">uint</span>
Number <span class="hljs-keyword">string</span>
}
<span class="hljs-keyword">var</span> card CreditCard
db.Model(&amp;user).Related(&amp;card, <span class="hljs-string">&quot;CreditCard&quot;</span>)
<span class="hljs-comment">//// SELECT * FROM credit_cards WHERE user_id = 123; // 123 is user&apos;s primary key</span>
<span class="hljs-comment">// CreditCard is user&apos;s field name, it means get user&apos;s CreditCard relations and fill it into variable card</span>
<span class="hljs-comment">// If the field name is same as the variable&apos;s type name, like above example, it could be omitted, like:</span>
db.Model(&amp;user).Related(&amp;card)
</code></pre>
<p><em>Specify Foreign Key</em></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Profile <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
UserRefer <span class="hljs-keyword">uint</span>
}
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Profile Profile <span class="hljs-string">`gorm:&quot;ForeignKey:UserRefer&quot;`</span>
}
</code></pre>
<p><em>Specify Foreign Key &amp; Association Key</em></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Profile <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
UserID <span class="hljs-keyword">uint</span>
}
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Refer <span class="hljs-keyword">uint</span>
Profile Profile <span class="hljs-string">`gorm:&quot;ForeignKey:UserID;AssociationForeignKey:Refer&quot;`</span>
}
</code></pre>
<h2 id="has-many">Has Many</h2>
<pre><code class="lang-go"><span class="hljs-comment">// User has many emails, UserID is the foreign key</span>
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Emails []Email
}
<span class="hljs-keyword">type</span> Email <span class="hljs-keyword">struct</span> {
gorm.Model
Email <span class="hljs-keyword">string</span>
UserID <span class="hljs-keyword">uint</span>
}
db.Model(&amp;user).Related(&amp;emails)
<span class="hljs-comment">//// SELECT * FROM emails WHERE user_id = 111; // 111 is user&apos;s primary key</span>
</code></pre>
<p><em>Specify Foreign Key</em></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Profile <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
UserRefer <span class="hljs-keyword">uint</span>
}
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Profiles []Profile <span class="hljs-string">`gorm:&quot;ForeignKey:UserRefer&quot;`</span>
}
</code></pre>
<p><em>Specify Foreign Key &amp; Association Key</em></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Profile <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
UserID <span class="hljs-keyword">uint</span>
}
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Refer <span class="hljs-keyword">uint</span>
Profiles []Profile <span class="hljs-string">`gorm:&quot;ForeignKey:UserID;AssociationForeignKey:Refer&quot;`</span>
}
</code></pre>
<h2 id="many-to-many">Many To Many</h2>
<pre><code class="lang-go"><span class="hljs-comment">// User has and belongs to many languages, use `user_languages` as join table</span>
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Languages []Language <span class="hljs-string">`gorm:&quot;many2many:user_languages;&quot;`</span>
}
<span class="hljs-keyword">type</span> Language <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
}
db.Model(&amp;user).Related(&amp;languages, <span class="hljs-string">&quot;Languages&quot;</span>)
<span class="hljs-comment">//// SELECT * FROM &quot;languages&quot; INNER JOIN &quot;user_languages&quot; ON &quot;user_languages&quot;.&quot;language_id&quot; = &quot;languages&quot;.&quot;id&quot; WHERE &quot;user_languages&quot;.&quot;user_id&quot; = 111</span>
</code></pre>
<p>*With back-reference :</p>
<pre><code class="lang-go"><span class="hljs-comment">// User has and belongs to many languages, use `user_languages` as join table</span>
<span class="hljs-comment">// Make sure the two models are in different files</span>
<span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
gorm.Model
Languages []Language <span class="hljs-string">`gorm:&quot;many2many:user_languages;&quot;`</span>
}
<span class="hljs-keyword">type</span> Language <span class="hljs-keyword">struct</span> {
gorm.Model
Name <span class="hljs-keyword">string</span>
Users []User <span class="hljs-string">`gorm:&quot;many2many:user_languages;&quot;`</span>
}
db.Model(&amp;language).Related(&amp;users)
<span class="hljs-comment">//// SELECT * FROM &quot;users&quot; INNER JOIN &quot;user_languages&quot; ON &quot;user_languages&quot;.&quot;user_id&quot; = &quot;users&quot;.&quot;id&quot; WHERE (&quot;user_languages&quot;.&quot;language_id&quot; IN (&apos;111&apos;))</span>
</code></pre>
<p><em>Specify Foreign Key &amp; Association Key</em></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> CustomizePerson <span class="hljs-keyword">struct</span> {
IdPerson <span class="hljs-keyword">string</span> <span class="hljs-string">`gorm:&quot;primary_key:true&quot;`</span>
Accounts []CustomizeAccount <span class="hljs-string">`gorm:&quot;many2many:PersonAccount;AssociationForeignKey:idAccount;ForeignKey:idPerson&quot;`</span>
}
<span class="hljs-keyword">type</span> CustomizeAccount <span class="hljs-keyword">struct</span> {
IdAccount <span class="hljs-keyword">string</span> <span class="hljs-string">`gorm:&quot;primary_key:true&quot;`</span>
Name <span class="hljs-keyword">string</span>
}
</code></pre>
<h2 id="polymorphism">Polymorphism</h2>
<p>Supports polymorphic has-many and has-one associations.</p>
<pre><code class="lang-go"> <span class="hljs-keyword">type</span> Cat <span class="hljs-keyword">struct</span> {
Id <span class="hljs-keyword">int</span>
Name <span class="hljs-keyword">string</span>
Toy Toy <span class="hljs-string">`gorm:&quot;polymorphic:Owner;&quot;`</span>
}
<span class="hljs-keyword">type</span> Dog <span class="hljs-keyword">struct</span> {
Id <span class="hljs-keyword">int</span>
Name <span class="hljs-keyword">string</span>
Toy Toy <span class="hljs-string">`gorm:&quot;polymorphic:Owner;&quot;`</span>
}
<span class="hljs-keyword">type</span> Toy <span class="hljs-keyword">struct</span> {
Id <span class="hljs-keyword">int</span>
Name <span class="hljs-keyword">string</span>
OwnerId <span class="hljs-keyword">int</span>
OwnerType <span class="hljs-keyword">string</span>
}
</code></pre>
<p>Note: polymorphic belongs-to and many-to-many are explicitly NOT supported, and will throw errors.</p>
<h2 id="association-mode">Association Mode</h2>
<p>Association Mode contains some helper methods to handle relationship things easily.</p>
<pre><code class="lang-go"><span class="hljs-comment">// Start Association Mode</span>
<span class="hljs-keyword">var</span> user User
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>)
<span class="hljs-comment">// `user` is the source, it need to be a valid record (contains primary key)</span>
<span class="hljs-comment">// `Languages` is source&apos;s field name for a relationship.</span>
<span class="hljs-comment">// If those conditions not matched, will return an error, check it with:</span>
<span class="hljs-comment">// db.Model(&amp;user).Association(&quot;Languages&quot;).Error</span>
<span class="hljs-comment">// Query - Find out all related associations</span>
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Find(&amp;languages)
<span class="hljs-comment">// Append - Append new associations for many2many, has_many, will replace current association for has_one, belongs_to</span>
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Append([]Language{languageZH, languageEN})
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Append(Language{Name: <span class="hljs-string">&quot;DE&quot;</span>})
<span class="hljs-comment">// Delete - Remove relationship between source &amp; passed arguments, won&apos;t delete those arguments</span>
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Delete([]Language{languageZH, languageEN})
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Delete(languageZH, languageEN)
<span class="hljs-comment">// Replace - Replace current associations with new one</span>
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Replace([]Language{languageZH, languageEN})
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Replace(Language{Name: <span class="hljs-string">&quot;DE&quot;</span>}, languageEN)
<span class="hljs-comment">// Count - Return the count of current associations</span>
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Count()
<span class="hljs-comment">// Clear - Remove relationship between source &amp; current associations, won&apos;t delete those associations</span>
db.Model(&amp;user).Association(<span class="hljs-string">&quot;Languages&quot;</span>).Clear()
</code></pre>
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<script src="gitbook/gitbook-plugin-search/search.js"></script>
<script src="gitbook/gitbook-plugin-lunr/lunr.min.js"></script>
<script src="gitbook/gitbook-plugin-lunr/search-lunr.js"></script>
<script src="gitbook/gitbook-plugin-sharing/buttons.js"></script>
<script src="gitbook/gitbook-plugin-fontsettings/fontsettings.js"></script>
</body>
</html>
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