Business Component Development with EJB Technology - Module 05

Module 5
Implementing Entity Classes : Modelling Data Association Relationships

Objectives

Upon completion of this module, you should be able to:

• Examine association relationships in the data and object models 
• Use relationship properties to define associations 
• Implement one-to-one unidirectional associations 
• Implement one-to-one bidirectional associations 
• Implement many-to-one/one-to-many bidirectional associations 
• Implement many-to-many bidirectional associations 
• Implement many-to-many unidirectional associations 
• Examine fetch and cascade mode settings

Relationships Within the Auction System’s Data Model

 

Object Model Showing Object Association Relationships 

Using Relationship Properties to Define Associations

• Cardinality: 

              •OneToOne 

              •ManyToOne 

              •OneToMany 

              •ManyToMany 

• Direction: 

              •Bidirectional 

              •Unidirectional

• Ownership:

              •Owning side 
              •Inverse side 

• Cascade type (operation propagation): 

              •All 

              •Persist 

              •Merge 

              •Remove 

              •Refresh 

              •None

Cardinality - Direction Combinations

Examples of One-to-One Relationships

One-to-One Bidirectional Relationships

One-to-One Unidirectional Relationships

Examples of One-to-Many Relationships

One-to-Many Bidirectional Relationship

One-to-Many Unidirectional Relationships

Examples of Many-to-One Relationships

Many-to-One Unidirectional Relationships

Examples of Many-to-Many Relationships

Many-to-Many bidirectional Relationships

Many-to-Many Unidirectional Relationships

Implementing One-to-One Unidirectional Association 

Implementing One-to-One Bidirectional Association

Implementing One-to-Many / Many-to-One Bidirectional Association

Implementing Many-to-Many Bidirectional Association

Fetch Mode Attribute

@ManyToOne(fetch=EAGER) 

private Customer customer; 

• EAGER 
• LAZY

Fetch Mode Default Values 

Cascade Mode Attribute

@OneToOne(cascade=PERSIST) 

private Customer customer;

Cascade mode attribute values

• PERSIST 
• MERGE 
• REMOVE 
• REFRESH 
• ALL