> For the complete documentation index, see [llms.txt](https://www.apibuilder.com/home/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.apibuilder.com/home/entities/relationships.md).

# Relationships

**Types of Relationships**:

* **One-to-One**: A relationship where a single record in one entity is associated with a single record in another. For instance, a user and a user profile.
* **One-to-Many**: A common relationship where a record from one entity can be associated with multiple records in another. For example, a single customer having multiple orders.
* **Many-to-Many**: This involves two entities that can have multiple records related to multiple records in the other entity. Many-to-many relationships often require a join table or entity.
* **Defining Relationships**: When defining a relationship, select the type of relationship, specify the related entities, and if necessary, define the join entity for many-to-many relationships.

In API Builder, by March 7, 2024 we have implemented support for creating **"one-to-many"** relationships between entities. This type of relationship allows one entity to be associated with multiple records of another entity, widely used for modeling hierarchical and related data in applications.

#### How to Create a "One-to-Many" Relationship

<figure><img src="/files/fuHrEeyviz6sURjjcUdm" alt=""><figcaption></figcaption></figure>

1. Select the Target Entity: In the API Builder interface, select the entity for which you want to create a relationship. (target reference not a source)
2. Go to Relationships tab
3. Click 'Add a Relationship' button&#x20;
4. Fill out the form&#x20;

<figure><img src="/files/GJkHbk95VzrCxiEBVRbx" alt=""><figcaption></figcaption></figure>

5. Save the Relationship: After configuring the relationship parameters, save the changes. API Builder will automatically update the entity models and generate the corresponding API endpoints for managing the related data.

For example: In the "Source" field, enter "List". For "Source Reference", enter "List", and for "Target Reference", use "Tasks" (plural). This configuration establishes a "one-to-many" relationship between the "List" and "Task" entities, indicating that one "List" can contain multiple "Tasks".

<figure><img src="/files/9iCj8YHXgWGLKdghsOpb" alt=""><figcaption></figcaption></figure>

**Source primary** and **Source optional** checks&#x20;

**How to update the Relationship**&#x20;