# polymorphicBelongsTo
## Usage
A `polymorphicBelongsTo` relationship is a `many-to-one` relationship. This relationship is used when an entity can belong to multiple types of entities. The classic example for this type of relationship is `Posts`, `Videos`, and `Comments`. For instance, a `Comment` may belong to a `Post` or a `Video`.
```javascript
// Comment.cfc
component extends="quick.models.BaseEntity" accessors="true" {
function post() {
return polymorphicBelongsTo( "commentable" );
}
}
```
The only value passed to `polymorphicBelongsTo` is a `prefix` for the polymorphic type. A common convention where is to add `able` to the end of the entity name, though this is not automatically done. In our example, this prefix is `commentable`. This tells quick to look for a `commentable_type` and a `commentable_id` column in our `Comment` entity. It stores our entity's mapping as the `_type` and our entity's primary key value as the `_id`.
When retrieving a `polymorphicBelongsTo` relationship the `_id` is used to retrieve a `_type` from the database.
The inverse of `polymorphicBelongsTo` is also `polymorphicHasMany`. 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
// Post.cfc
component extends="quick.models.BaseEntity" accessors="true" {
function comments() {
return polymorphicHasMany( "Comment", "commentable" );
}
}
```
```javascript
// Video.cfc
component extends="quick.models.BaseEntity" accessors="true" {
function comments() {
return polymorphicHasMany( "Comment", "commentable" );
}
}
```
## Signature
| Name | Type | Required | Default | Description |
| ------------------ | ------------------- | -------- | ------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| name | String | `false` | `relationMethodName` | The name given to the polymorphic relationship. |
| type | String | `false` | `name & "_type"` | The column name that defines the type of the polymorphic relationship. |
| id | String | `false` | `name & "_id"` | The column name that defines the id of the polymorphic relationship. |
| localKey | String \| \[String] | `false` | `related.keyNames()` | The column name on the `realted` entity that is referred to by the `foreignKey` of 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 polymorphicBelongsTo relationship between this entity and the entity defined by `relationName`.
## Visualizer
{% embed url="" %}