Question

Fill in the blanks in each of the following: a) For entity EJBs that use ______ persistence to represent data in a relational database, the ______ must specify SQL queries when deploying the EJB. b) For entity EJBs that use ______ persistence to represent data in a relational database, the ______ must implement code that synchronizes data with the database. c) Each create method in the home interface must have a corresponding ______ method in the EJB implementation. d) If an entity EJB has a complex primary key, the developer must provide a custom ______ that represents the complex primary key.

Short answer

(a) container-managed, container; (b) bean-managed, developer; (c) ejbCreate; (d) key class.

Step-by-step solution

Identifying the Type of Persistence

Entity EJBs can use either container-managed persistence or bean-managed persistence. For part a, entity EJBs that use container-managed persistence (CMP) require that the EJB container specifies SQL queries. For part b, entity EJBs that use bean-managed persistence (BMP) require developers to write the code that manages data synchronization.

Identifying Create and Corresponding Methods

Each create method in the home interface of an EJB must have a corresponding ejbCreate method in the EJB implementation. This is crucial for the creation of the entity instance.

Handling Complex Primary Keys

When an entity EJB has a complex primary key, the developer needs to provide a custom key class that implements the primary key. This class is designed to handle the composite values that make up the primary key in an EJB.

Key concepts

Container-Managed Persistence (CMP)

In the realm of Enterprise JavaBeans (EJB), container-managed persistence (CMP) is a method through which the EJB container automatically handles the interactions with the database. Essentially, with CMP, developers do not have to write SQL queries themselves because these details are abstracted away and managed by the container itself.
This leads to quicker development times as the complexities of SQL operations are handled transparently by the container.
CMP relies on metadata that is specified, usually in XML format, which allows the container to map Java objects to database tables seamlessly.
CMP excels in scenarios where the database schema is stable and does not require complex query logic. However, it may not offer the fine-grained control that some applications need for optimized database interaction.

• Automates SQL query handling
• Relies on metadata and XML for configuration
• Simplifies database interactions

Bean-Managed Persistence (BMP)

With bean-managed persistence (BMP), the responsibility of managing database interactions shifts to the developer. This means that developers must manually implement all the SQL queries and data synchronization logic required for the entity EJBs to interact with the database.
While this requires more effort and expertise in SQL from the developers, BMP offers greater flexibility in how database operations are handled.
Developers can optimize queries and customize interactions for specific performance needs, making BMP useful in complex database scenarios where a one-size-fits-all approach isn't feasible.

• Developer writes custom SQL queries
• Allows for detailed optimization
• Greater control over database transactions

SQL Queries

Structured Query Language (SQL) forms the backbone of interactions with relational databases. In the context of entity EJBs, SQL queries are essential for fetching, inserting, updating, and deleting data within the database.
Using CMP, the EJB container handles these SQL queries implicitly, while with BMP, developers must explicitly write and manage every SQL query.
These queries must adhere to the standards of SQL which include operations such as

• SELECT: retrieves data from the database
• INSERT: adds new data entries
• UPDATE: modifies existing data
• DELETE: removes data entries

By understanding and crafting efficient SQL queries, developers can significantly influence an application's performance, responsiveness, and scalability.

Complex Primary Key

A complex primary key in entity EJBs refers to a primary key that consists of multiple columns or fields, rather than a single one. When working with complex data models, a singular field may not be sufficient to ensure unique identity for data records. Thus, developers are required to define a custom class implementing the `Serializable` interface.
This custom class encapsulates all the fields that constitute the primary key.
Designing this class thoughtfully is important as it allows the entity EJB to correctly identify and manage the unique data records based on the composite values.
This ensures integrity and efficient access to the entities in a database where more than one attribute is necessary to uniquely identify an entity.

• Comprises multiple fields
• Requires custom class implementation
• Used for unique entity identification