Context Object
Context, Encapsulate Context
Decouple data from protocol-specific classes and store the scoped data in an object independent
of the underlying protocol technology.
Real-world example
Object provides an abstract interface to some type of database or other persistence mechanism.
Real world example
There's a set of customers that need to be persisted to database. Additionally we need the whole
set of CRUD (create/read/update/delete) operations so we can operate on customers easily.
Ensures that each object gets loaded only once by keeping every loaded object in a map.
Looks up objects using the map when referring to them.
Real world example
We are writing a program which the user may use to find the records of a given person in a database.
Holds details of object-relational mapping in the metadata.
Real world example
Hibernate ORM Tool uses Metadata Mapping Pattern to specify the mapping between classes and tables either using XML or annotations in code.
Provide an ability to avoid concurrent changes of one record in relational databases.
Each transaction during object modifying checks equation of object's version before start of transaction
and before commit itself.
Real world example
Private Class Data design pattern seeks to reduce exposure of attributes by limiting their
visibility. It reduces the number of class attributes by encapsulating them in single Data object.
Real world example
Imagine you are cooking a stew for your family for dinner. You want to prevent your family members
from consuming the stew by tasting it while you are cooking, otherwise there will be no more stew
for dinner later.
Repository layer is added between the domain and data mapping layers to isolate domain objects from
details of the database access code and to minimize scattering and duplication of query code. The
Repository pattern is especially useful in systems where number of domain classes is large or heavy
querying is utilized.
Resource Acquisition Is Initialization pattern can be used to implement exception safe resource management.
Use the Resource Acquisition Is Initialization pattern when
To easily persist Java objects to the database.
Java serialization allow us to convert the object to a set of bytes. We can store these bytes into database as
BLOB(binary long objects) and read them at any time and reconstruct them into Java objects.
Service Layer is an abstraction over domain logic. It defines application's boundary with a layer of services that
establishes a set of available operations and coordinates the application's response in each operation.
Typically applications require different kinds of interfaces to the data they store and the logic they implement.
Despite their different purposes, these interfaces often need common interactions with the application to access and
manipulate its data and invoke its business logic. Encoding the logic of the interactions separately in each module
causes a lot of duplication. It's better to centralize building the business logic inside single Service Layer to avoid
these pitfalls.
