Data layer

As explained in Java Persistence with Spring Data and Hibernate epub

The persistence layer is the architectural layer responsible for loading and storing domain-model state in durable storage.

The data layer, also called the persistence layer, stores domain-model state in durable storage and retrieves it when the application needs it. It sits between the business layer and the external database: business logic works with domain entities, while persistence components preserve those entities’ state. section 3.1.1

Figure 3.1 A persistence layer is the basis of a layered architecture.

Use the layered-architecture figure to place the persistence layer beneath domain-model operations and above the database. section 3.1.1

A well-separated data layer keeps responsibilities distinct:

• The presentation layer renders domain-entity state for users. section 3.2.1
• The business layer executes rules and calculations against domain entities. section 3.1.1
• The persistence layer loads entities from and stores them in the database. section 3.2.1
• The database holds the system state for the long term, usually through a schema and possibly stored procedures. section 3.1.1

Separating persistence concerns prevents domain logic from depending on a particular container, runtime environment, or service mock. A domain method such as Item#calculateTotalPrice() can therefore run against in-memory state in a unit test, while database loading and storing remain persistence or integration concerns. section 3.2.1 section 10.1

Persistence is transparent when entity classes do not need to know whether their state is temporary or durable. JPA defines the entity class as the primary programming artifact; Hibernate provides an ORM implementation, and metadata such as annotations or XML lets the runtime apply persistence and transaction behavior generically. section 3.2.1

At runtime, the application interacts with Jakarta Persistence to load or store state. A persistence context remembers changes within a unit of work, while entity states and managed scope determine how an instance participates in that lifecycle. section 10.1

How Java Persistence with Spring Data and Hibernate epub covers it

How deep it goes

Defines responsibilities, transparent persistence, entity lifecycle, persistence contexts, and units of work without detailing provider-specific mappings.

Examples

Uses a layered-architecture figure, Item#calculateTotalPrice(), unit tests, entity classes, annotations, XML descriptors, and persistence contexts.

What it assumes

Assumes domain entities and layered applications, while introducing persistence contexts, entity lifecycle, and units of work.

What you can do after

Apply it by separating domain tests from database integration and organizing JPA-based loading, storing, and lifecycle management.

How it connects

Connects layered architecture, domain models, databases, JPA, Hibernate, ORM, transactions, entity states, and persistence contexts.

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Related concepts

• feature engineeringhas part · Feature engineering is the creation, transformation, or selection of input features from data to provide useful representations for analysis or modeling.
• four-layer architecturepart of · A four-layer architecture organizes a system into four distinct layers, each with separate responsibilities.
• pipelinehas part · A pipeline is an ordered or coordinated sequence of connected processing stages or tasks that passes data, work, or results toward an outcome.
• databaseuses · A database is an organized collection of persistent data managed by software for storage, retrieval, querying, and modification.
• multi-tier applicationpart of · A multi-tier application is an application organized into distinct tiers that separate responsibilities and interact through defined dependencies or interfaces.

This explainer was generated by Manning's knowledge graph from the text of Java Persistence with Spring Data and Hibernate epub. The section links point to the parts of the book it draws on.