To implement a one-to-many relationship in Spring with a RESTful API, you will need to define two entities: the parent entity and the child entity. In this case, the parent entity is the entity that has a one-to-many relationship with the child entity.

Here is an example of how you can define these entities in Spring:

Parent entity:

@Entity
public class Parent {
@Id
@GeneratedValue
private Long id;

@OneToMany(mappedBy = "parent", cascade = CascadeType.ALL)
private List<Child> children;

// other fields, getters, and setters
}

Child entity:

@Entity
public class Child {
@Id
@GeneratedValue
private Long id;

@ManyToOne
@JoinColumn(name = "parent_id")
private Parent parent;

// other fields, getters, and setters
}

To create a one-to-many relationship between a parent and a child, you will need to create a parent entity and then create multiple child entities that are associated with that parent. You can do this by setting the parent field of each child entity to the parent entity.

To create a new parent and child using a RESTful API, you can use the following HTTP request:

POST /parents
{
"children": [
{
// child entity data
},
{
// child entity data
}
]
}

This will create a new parent entity and two child entities that are associated with that parent. The children field in the request body is an array of child entities that will be associated with the parent.

To retrieve the children for a particular parent, you can use the following HTTP request:

GET /parents/{parentId}/children

This will return a list of all the children that are associated with the parent entity with the specified parentId.