BCD Session 07

8/10/2019 BCD Session 07

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Business Component Development Using EJB Technologies

In this session, you will learn to:

Examine association relationships in the data and object

models

Use relationship properties to define associations

Implement one-to-one unidirectional associationsImplement 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

Objectives


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Examining Association Relationships in Data and Object Models

The following figure shows some of the relationships within

the data model that represents the auction application in the

EIS tier.


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Examining Association Relationships in Data and Object Models (Contd.)

The following figure shows the object model that is used to

represent the auction application in the middle tier.

Auction

Bid

Item

1 1

1 *


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Using Relationship Properties to Define Associations

The properties that describe association relationships

between objects in the object model are:

Cardinality

Direction

OwnershipCascade type


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Using Relationship Properties to Define Associations (Contd.)

Cardinality specifies the quantity relationship between two

entities in a relationship and it is expressed using one of the

following annotations:

OneToOne

ManyToOne

OneToMany

ManyToMany

Direction implies navigation or visibility and is expressed

using one of the following terms:

BidirectionalUnidirectional


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Using Relationship Properties to Define Associations (Contd.)

Ownership specifies the owning side of the relationship. The

different types of ownerships are:

Owning side

Inverse side

Cascade property specifies the propagation of the effect ofan operation to associated entities and is expressed using

one of the following terms:

All

Persist

MergeRemove

Refresh

None


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Examples of Association Relationships

The following table shows the seven possible

cardinality-direction combinations.

Cardinali ty Direction

One-to-one Bidirectional

One-to-one Unidirectional

One-to-many Bidirectional

One-to-many Unidirectional

Many-to-one Unidirectional

Many-to-many Bidirectional

Many-to-many Unidirectional




Examples of Association Relationships (Contd.)

The following figure shows an example of a one-to-one

bidirectional relationship.

The following figure shows an example of a one-to-one

unidirectional relationship.

Car_1 Engine_1

Auction_1 Item_1





The following figure shows an example of a many-to-one/

one-to-many bidirectional relationship.

The following figure shows an example of a one-to-many


Auction_1

Bid_1

Order_1

OrderItem_1


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The following figure shows an example of a many-to-one

unidirectional relationships.

AccountType_1

Account_1


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The following figure shows an example of many-to-many

bidirectional relationship.

Employee_1

Employee_2

Employee_3

Employee_4Company_3

Company_2

Company_1


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The following figure shows an example of many-to-many



InventoryItem_1

Order_3

Order_2

Order_1

InventoryItem_2

InventoryItem_3

InventoryItem_4


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Implementing One-to-One Unidirectional Association

The following figure shows a one-to-one unidirectional

association between two entities.


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Implementing One-to-One Unidirectional Association (Contd.)

The following code shows an example of the owning side of

a unidirectional one-to-one relationship:1 @Entity

2 public class Customer {

3 @Id

4 private int id;

5 @OneToOne

6 private Record custRecord;

7 ..// }


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The following figure shows the table with join column

matching the corresponding entities.

Implementing One-to-One Unidirectional Association (Contd.)


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Implementing One-to-One Bidirectional Association

The following figure shows a one-to-one bidirectional



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The following code shows a bidirectional one-to-one

association owning entity example:1 @Entity


3 @Id

4 private int id;

5 @OneToOne

6 private Record custRecord;

7 ..//

8 }

Implementing One-to-One Bidirectional Association (Contd.)


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The following table shows the join columns matching with

the corresponding entities.

Implementing One-to-One Bidirectional Association (Contd.)


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

The following figure shows a one-to-many/many to one

bidirectional association between two entities.


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The following code shows a bidirectional one-to-many

relationship:1 @Entity


3 @Id

4 private int id;

5 @OneToMany(mappedBy=customer)

6 private Collection orders;

7 ..//

8 }

Implementing One-to-Many/Many-to-One Bidirectional Association (Contd.)


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The following code shows a bidirectional many-to-many

relationship:1 @Entity

2 public class Order {

3 @Id

4 private int orderId;

5 @ManyToOne

6 private Customer customer;

7 ..//

8 }



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The following figure shows the table with join columns

matching the corresponding entities.



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Implementing Many-to-Many Bidirectional Association

The following figure shows many-to-many bidirectional



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Implementing Many-to-Many Bidirectional Association (Contd.)

The following code shows an example of the owning side of

a bidirectional many-to-many relationship:1 @Entity

2 public class Worker {

3 @Id

4 private int id;

5 @ManyToMany

6 private Set projects;

7 ..//

8 }


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The following figure shows the table with join columns

matching the corresponding entities for one-to-many/

many-to-one bidirectional association.

Implementing Many-to-Many Bidirectional Association (Contd.)


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Examining Fetch and Cascade Mode Settings

The Association mapping annotations attributes are:

Fetch mode

Cascade mode

All annotations that specify association mappings have a

fetch mode attribute.The container interprets the fetch mode setting as:

EAGER

LAZY


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Fetch Mode Attribute

The following table lists the default values for annotations.

Annotat ion Default

Basic EAGER

OneToOne EAGER

ManyToOne EAGER

OneToMany LAZY

ManyToMany LAZY


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Cascade mode settings are used when the EntityManagerAPI is invoked.

The following table describes the possible values for the

cascade attribute.

Cascade Mode Attribute

Value Comment

PERSIST Causes the persist operation to cascade to the target entity of the association

when the entity managers persist operation is invoked on the source entity.

MERGE Causes the merge operation to cascade to the target entity of the association

when the entity managers merge operation is invoked on the source entity.

REMOVE Causes the remove operation to cascade to the target entity of the association

when the entity managers remove operation is invoked on the source entity.

REFRESH Causes the refresh operation to cascade to the target entity of the association

when the entity managers refresh operation is invoked on the source entity.

ALL Causes all the entity state change operations (persist, merge, remove, and

refresh) to cascade to the target entity of the association.


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In this session, you learned that:

The properties that describe association relationships between

objects in the object model are:

Cardinality

Direction

Ownership

Cascade type

The different types of ownerships are:

Owning side

Inverse side

Summary


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The Cascade propertyis expressed using one of the following

terms:

All

Persist

Merge

RemoveRefresh

None

The Association mapping annotations attributes are:

Fetch mode

Cascade mode

The container interprets the fetch mode setting as:

EAGER

LAZY

Summary (Contd.)

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BCD Session 07

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