April 10, 2023 Copyright Jim Farley

Beyond JDBC: Java Object-Relational

MappingsJim Farley

e-Commerce Program Manager

GE Research and Developmentfarley@crd.ge.com

April 10, 2023 Copyright Jim Farley

Agenda

• Define the problem• Review the issues and options

– Design approaches– Technical tools

• Some guidelines for choosing a solution

April 10, 2023 Copyright Jim Farley

The Problem

• Impedance mismatch– OOP vs. RDBMS

• Both still prominent in their respective domains

• Both designed for different purposes– OO: Conceptual program design– RDBMS: Data relationship modeling

and access speed

April 10, 2023 Copyright Jim Farley

The Building Blocks

• OOP– Interfaces, classes– Data member references– Methods

• RDBMS– Tables, columns– Foreign keys, integrity constraints– Stored procedures

April 10, 2023 Copyright Jim Farley

Goals and Assumptions• Optimize “conceptual accuracy” and

robustness of OOP objects• Optimize robustness of data model

– Multiple use-cases, some non-Java apps• Online apps + reporting tools + OLAP

• JDBC is the underlying plumbing (directly or indirectly)

• Minimize latency of JDBC “bridge” code• Preserve “ACID” properties of database

April 10, 2023 Copyright Jim Farley

The Framework

RDBMS

DO

DODO

Application/Business Object

Application/Business Object

Application/Business Object

Application/Business Object

Data layer(RDBMS “objects”)

Conceptual layer(Java objects)

Middleware(Java objects)

April 10, 2023 Copyright Jim Farley

Why define a mapping?• Encapsulates the data access layer

– Preserve data-level business rules– Minimize impact on code due to data model

changes

• Reduces development overhead– Schema plus the mapping rules is all you need

to know to use the database

• Simplifies code management– Mapping is a shield/guide for introducing

fixes

April 10, 2023 Copyright Jim Farley

Some Common Approaches• Schema -> JDBC abstraction -> app

objects– Non-remote by default, can be wrapped– Low overhead/high transaction rates– Context-independent

• Schema-> XML binding -> app objects• Schema -> EJB entity beans -> app objects

– Remote by default– J2EE compliant

April 10, 2023 Copyright Jim Farley

Issues

• Reproducible mapping?• Where does the business logic go?• Who defines the transaction

boundaries?• How does the security model tie

in?

April 10, 2023 Copyright Jim Farley

Reproducible Mappings• I.e., no hand-tweaking of the generated

code…• Pros:

– Schema changes can be tracked easily– Every set of data objects is consistent

• Cons:– Mapping utility needs to support full access

to data layer– Possibility for sub-optimal data access

April 10, 2023 Copyright Jim Farley

Reproducible Mappings

• Recommendation: Keep the mapping reproducible– Adjusting the mapping utility rather

than the code is almost always a bigger payback

– Data access can be optimized in the mapping, or by allowing for app-layer “back-doors” to the JDBC level

April 10, 2023 Copyright Jim Farley

Business Logic

• Possibilities:– App-layer (above the generated data objects)– Hand-tweak the data layer– Stored procedures

• “Business logic” comes in different flavors– Data integrity– Higher-level business process/workflow– Authorization

April 10, 2023 Copyright Jim Farley

Business Logic• Recommendations:

– Don’t tweak the data layer• Too messy, easier to adjust mapping utility to access

it

– Look at the usage modalities you need to support and let that drive the decisions• E.g., Two-tier reporting/admin tools => more data

integrity logic and authorization in stored procedures

– Generally speaking:• Keep data integrity close to the database level• Keep business process/workflow out in the app level

April 10, 2023 Copyright Jim Farley

Transaction Boundaries

• I.e., What operations make up an ACID transaction?

• Largely driven by business-logic decisions– “Hard-coding” a transaction in the mapping

layer implicitly places business logic there as well

– Some logic will go into app-layer => pass-through support in data layer

– Some logic may go into the RDBMS => multi-tier transactions

April 10, 2023 Copyright Jim Farley

Transaction Boundaries• Recommendations:

– Keep data-layer transactions fairly atomic, allow for subsuming them into higher-level transactions

– Get intimate knowledge of how RDBMS and JDBC driver work together to support transactions• Data layer interactions with stored

procedures => tiered transactions• Can/will affect transaction rates

April 10, 2023 Copyright Jim Farley

Security Model

• Authentication and authorization need to be supported top to bottom

• User identities and policies need to be mapped to RDBMS level

• RDBMS security support is erratic– Some do certificates, some don’t

• Account management– Roles, access modalities, etc. play into this

April 10, 2023 Copyright Jim Farley

Security Model• Recommendation: Keep policies out of the

data layer– Provide pass-through support in the mapping– Try to avoid vendor-specific facilities in the

mapping layer

• You may need to “bridge” PKI with RDBMS authorization– Map user accounts to database accounts– Data relationships in the RDBMS, business

rules in the app layer

April 10, 2023 Copyright Jim Farley

Solutions: Custom mapping• JDBC/schema -> abstraction layer -> app

objects– Abstraction layer provides entities that

represent tables, columns, procedures, constraints, etc.

– RDBMS “objects” mapped to “instances” of these entities (subclasses, wrappers)

• Non-remote, optimizable, portable• Transactions and security are all up to you• Have to worry about driver issues yourself

April 10, 2023 Copyright Jim Farley

Solutions: EJB Entity beans• JDBC/schema -> EJB entity beans -> app

objects• App objects can be session beans,

higher-order entity beans, etc.• Remote by default, EJB engine required• Transactions directly supported

– But transaction rates will be lower

• Container-managed persistence is an option

April 10, 2023 Copyright Jim Farley

Solutions: XML

• Schema-> XML binding -> app objects– Or some variation?

• XML binding plus standard schema language would extend portability enormously– Publish your schema and business components– Generate optimized RDBMS and middleware

• But: Not ready for prime time• But: No relationship with EJB defined (yet)

April 10, 2023 Copyright Jim Farley

Overall Recommendations• EJB is a nice framework, use it if you can

afford it– Transaction rates need to be improved– Server costs may not make sense for you– Still need a mapping of some kind

• Custom middleware is a pain, but still an option– Third-party stuff is there, but be careful

• Watch the XML space for a “right” solution

April 10, 2023 Copyright Jim Farley

Questions?