Understand JPA entity relationship, Many to One, One To Many, Many To Many

[kpnishanth]

• ManyToOne Many side is the Owner
• Owner side is responsible for maintaining the foreign key relationship.
• OneToMany and ManyToOne fetch lazily by default.
• Many Side of the relationship usually represnted by LIst, Map or Sets.

JPQL:

• @Query annotation at Repository method level. You can use Named Parameters using @Param and positions place holders as well.
• @Query(value="query", nativeQuery=true)

@NamedQuery:

• This is at Entity level
• Add the @NamedQuery annotation in the entity class level
• Add attributes Name, value =query (jpql)
• IN the Repositoy method directly calll the named query using the method name equal toname attribute name of namedQuery
• @NamedQueries can be used for adding multiple queries

@NamedNativeQuery

• In the entity class add @namedNativeQuery annotation.
• add name and value attributes
• In the Reposiitory method add @Query(nativeQuery=true) -@NamedNativeQueries can be used for adding multiple @NamedNativeQueries

Pagination and Sorting:

• Pagable interface and Page object
• Pageable wil be passed with details of number of lines in page, page size etc..
• Page will be retured as Object with the details of cuurent page,, number of total pages. details of current page., total number of records etc..
• Sort method can be used of providing sort details.
• Use Sort.and(sort) to add multiple conditions for sort