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Chapter 14: Spring Data

What is Spring Data

  • Spring Data refers to a familly of modules that aim to provide a unified interface for dealing with differnet underlying persistance technologies

  • There is spring data for JDBC, JPA, mongoDB etc..

  • It's goal is to write the persitance using the abstarctions provided which are common to various technologies

  • Spring is responsible for providing the implementations to these interfaces

  • We will be examining Spring Data JDBC in this chapter where spring data fits

The Spring Data Hirearchy

  • To follow the interface segragation principle, spring provides a hirarchy for interfaces each one extending the other and providing additional functionality on top of it

  • This hirarachy is there to avoid having on big interface that has fucntionality we don't need

  • The inteface looks as following and even has inteface that only work with certain underlying technologies such as Hibernate spring data interface hirarchy

    • Respository: This interface is mainly used as a marker interface and extending it doesn't make spring implement any methods for us unless we specify these methods explicitly

    • CrudRepsitory: Spring provides an implementation for this interface, the implementations includes basic operations such as the finding item by primary key, updating records, etc

    • PagingAndSortingRepository: on top of the above provides implimentation for pagination capabilites and other advanced features

Using Spring Data

  • In all cases we only declare an interface that extend the Spring Data interfaces and some annotaions

  • The interface hirarchy created by this is scanned by spring and when it finds that our interface extends one of the Spring Data interfaces it generates a class implementing the interface, creates an instance of that class and injects it for us when we want to use it

  • Spring data not only implements the methods of the interface, it can also use our code and annotations to implement more functionality such as custom queries

  • Before anything Spring Data requires us to specify what the primary key of the object modelling the rows is

    public class Account {
    @Id
    private long id;
    private String name;
    private BigDecimal amount;
    // Omitted getters and setters
}

1. Using method naming conventions

  • Spring can parse the name of methods in a Spring Data repository and construct a method based on predefined naming conventions

    //the first object in generic is the object modelling the rows, the second is the datatype of the primary key
public interface AccountRepository extends CrudRepository<Account, Long> {
    List<Account> findAccountsByName(String name);
}

  • Spring will parse the above method name and generate SELECT * FROM account WHERE name = ?

2. Using @Query annotation

  • We can specify a custom query and bind it to a method as follows

    public interface AccountRepository extends CrudRepository<Account, Long> {
    @Query("SELECT * FROM account WHERE name = :name")
    List<Account> findAccountsByName(String name);

    @Modifying
    @Query("UPDATE account SET amount = :amount WHERE id = :id")
    void changeAmount(long id, BigDecimal amount);
}

  • Query's that modify the database must be annotated with@Query

  • The parameter names in the query should match the names of the parameters in the method signiture and no space should be between the parameter name and the :

3. Using pre-implemented methods

  • as we said before, spring provides implementations to the inteface.

  • some predefined methods are

    • deleteById(Id id)
    • findById(Id id)
    • etc...

We then proceed to inject the repsoitory we created and use the methods like normal methods et voila!