* **This class is never created directly. It should be constructed through associations in `Ext.data.Model`.*** an ecommerce system where Users can place Orders - there is a one to many relationship between these Models,* one user can have many orders (including 0 orders). Here is what a sample implementation of this association* A less common form of Many To One, a single entity (`A`) has a relationship with at most 1 entity (`B`). This is often* used when partitioning data. For example a `User` may have a single `UserInfo` object that stores extra* An entity (`A`) may have a have a relationship with many (`B`) entities. That (`B`) entity may also* have a relationship with many `A` entities. For example a single `Student` can have many `Subject` entities and* This can be defined using `Ext.data.schema.ManyToMany`. Many To Many relationships are readonly unless used with* A keyed association relies on a field in the model matching the id of another model. Membership is driven by the key.* This is declared using the ||reference|| configuration on a model field. An example of this can be seen* A keyless association relies on data hierarchy to determine membership. Items are members because they are* Assocations make it easier to work with Models that share a connection. Some of the main functionality includes:* Associated models will automatically generate named methods that allow for accessing the associated data.* Nested loading is the ability to load hierarchical associated data from a remote source within a single request.* In the following example, each `User` in the `users` store has an `orders` store. Each `orders` store is populated* with `Order` models read from the request. Each `Order` model also has a reference back to the appropriate `User`.* The role is used to determine generated names for an association. By default, the role is generated from* either the field name (in a keyed association) or the model name. This naming follows a pattern defined by* In the above example, the `Thread` will be decorated with a `comments` method that returns the store.* On records that have a "to many" relationship, a single methods that returns a `Ext.data.Store` is created.* Associations are reflexive. By declaring one "side" of the relationship, the other is automatically setup. In* the example below, there is no code in the `Thread` entity regarding the association, however by virtue of the* declaration in post, `Thread` is decorated with the appropriate infrastructure to participate in the association.