# hasOne
## Usage
A `hasOne` relationship is a "one-to-one" relationship. For instance, a `User` entity might have an `UserProfile` entity attached to it.
```javascript
// User.cfc
component extends="quick.models.BaseEntity" accessors="true" {
function profile() {
return hasOne( "UserProfile" );
}
}
```
The first value passed to `hasOne` is a WireBox mapping to the related entity.
Quick determines the foreign key of the relationship based on the entity name and key values. In this case, the `UserProfile` entity is assumed to have a `userId` foreign key. You can override this by passing a foreign key in as the second argument:
```javascript
return hasOne( "UserProfile", "FK_userID" );
```
If your parent entity does not use `id` as its primary key, or you wish to join the child entity to a different column, you may pass a third argument to the `hasOne` method specifying your parent table's custom key.
```javascript
return hasOne( "UserProfile", "FK_userID", "profile_id" );
```
The inverse of `hasOne` is [`belongsTo`](/8.0.0-1/guide/relationships/relationship-types/belongsto.md). It is important to choose the right relationship for your database structure. `hasOne` assumes that the related model has the foreign key for the relationship.
```javascript
// UserProfile.cfc
component extends="quick.models.BaseEntity" accessors="true" {
function user() {
return belongsTo( "User" );
}
}
```
## withDefault
`HasOne` relationships can be configured to return a default entity if no entity is found. This is done by calling `withDefault` on the relationship object.
```javascript
// User.cfc
component extends="quick.models.BaseEntity" accessors="true" {
function profile() {
return hasOne( "UserProfile" ).withDefault();
}
}
```
Called this way will return a new unloaded entity with no data. You can also specify any default attributes data by passing in a struct of data to `withDefault`.
```javascript
// User.cfc
component extends="quick.models.BaseEntity" accessors="true" {
function profile() {
return hasOne( "UserProfile" ).withDefault( {
"showHints": true
} );
}
}
```
## Signature
| Name | Type | Required | Default | Description |
| ------------------ | ------------------- | -------- | ------------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| relationName | string | `true` | | The WireBox mapping for the related entity. |
| foreignKey | String \| \[String] | `false` | `entityName() & keyNames()` | The foreign key on the parent entity. |
| localKey | String \| \[String] | `false` | `keyNames()` | The local primary key on the parent entity. |
| relationMethodName | String | `false` | The method name called on the entity to produce this relationship. | The method name called to retrieve this relationship. Uses a stack backtrace to determine by default.
\\
DO NOT PASS A VALUE HERE UNLESS YOU KNOW WHAT YOU ARE DOING.
|
Returns a HasOne relationship between this entity and the entity defined by `relationName`.
## Visualizer
{% embed url="" %}
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