We can use the below mapping for mapping Book class using Fieldresult mapping, and bookvalue using Constructorresult = "BookAuthorMapping",Įntities = Book.class, fields = "id", name = "title", name = "author_id", name = "version", name = "version")Ĭlasses = BookValue.10:56:51,671 INFO executeDdlStatements Executing DDL: drop table USER_RELATION For this we required a separate java class 'BookValue' to mapped the values from resultset. Here, we can observe that the resultset has been required field/columns from two different entities, i.e. SELECT b.id, b.title, b.version, a.firstName ||Ī.lastName as authorName, b.author_id FROM Book b JOIN Author a ON b.author_id = a.id Let's suppose below is the join query, we want to map each result row to Book, and Author class, if the same property name exists, we can use some alias name in either of the entities.
Now, let's understand about constructor mapping. We can use an orm.xml file also for specifying the mappings. Here, we can specify the AuthorMapping name, and target type of entity is Author class, and specifying the fieldresult including the column name entity property name. So, we need to write the annotation with the AuthorMapping = Author.class,įields = we are using Java 7 or below versions, then no support for annotations, we need to specify all these mappings inside = Author.class,įields = we are using Java 8 or greater version, then JDK supports annotation, then no need to specify annotation, we can directly specify any number of mappings. Here, we used the AuthorMapping SQLresultsetmapping name for mapping query result to the author entity. Results = em.createNativeQuery("SELECT a.id as authorId,Ī.firstName, a.lastName, a.version FROM Author a", "AuthorMapping").getResultList()
Hibernate java sql how to#
So, we will write a SQL resultset mapping without using JPQL query, understand how to use field results. The ‘entityName’ property allows to specify the entity name and ‘fields’ property allows to specify a set of for field/column definitions to be is the annotation to specify the mapping between the resultset column name and entity property is the annotation to specify the mapping entity constructor argument type and resultset column name.įirst, we will understand with default mapping in a custom mapping way. This annotation have two main properties ‘entityName’ & ‘fields’. This annotation have two main properties ‘name’ & ‘entities’ The ‘name’ property allows to specify the name of the mapping and ‘entities’ allows tospecify the java entity with is the annotation that contains entity name to be mapped and it’s field/column settings. Mappings also can be done in 2 ways either we can do the field mapping, or we can use the constructor to map is the annotation that contains all SQL resultset mapping for all native queries. These mapping can be done in two ways, either we can write in an annotation style, or we can write orm.xml and place in the MET-INF folder so that JPA provider will parse this, and do the mappings.Īnother way to write, JPA annotations and write the mapping using annotations. If more queries of these types are present, we need to write more mappings maintenance will not be an easy java job. We need to write some custom mapping for this. When the automatic mapping is not possible like, using some alias names or joining of column values, or if the query result needs to map to multiple entities, then these default mapping will not work. JPA 2.1 version supports these by using SQL result mapping so we can use any JPA provider implements 2.1 specifications. It will be more comfortable and easily maintainable if we can tell EntityManager to map the result of SQL query into entities. This will result in a lot of repeated code, and type cast to model variable type. You would have noticed that doing above required care for casting and extracting from object array. Long id = ((BigInteger) record).longValue() Results = em.createNativeQuery("SELECT a.id, a.firstName, a.lastName, a.version FROM Author a").getResultList()
We need to iterate this array, and cast each object to a specific type, and map them to a model through SQL server consulting. The downside of these is, it will return List instead of returning List of entity classes, each object array will hold the single row of the resultset. In most complex cases, JPQL is not powerful enough to write the queries we need to depend on the SQL native queries or stored procedures as well. JPQL is one of the most powerful languages for SQL to write the queries which will execute on all databases.
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