3/22/2021 0 Comments Sql To Jpql Converter Tool
This should not be done, but is sometimes desirable, in which case the query should ensure it has been set to BYPASS the cache.
![]() Select queries can return a single object or data element, a list of objects or data elements, or an object array of multiple objects and data. Query query em. createQuery ( Select e FROM Employee e WHERE e.salary 100000 ). Query query em. createQuery ( Select e FROM Employee e WHERE e.id:id ). Query query em. createQuery ( Select MAX(e.salary) FROM Employee e ). Query query em. createQuery ( Select e.firstName FROM Employee e ). Query query em. createQuery ( Select e.firstName, e.lastName FROM Employee e ). These functions can be used to return a single result, or can be used with a GROUP BY to return multiple results. These will not be managed objects, and the class must define a constructor that matches the arguments of the constructor and their types. Constructor queries can be used to select partial data or reporting data on objects, and get back a class instance instead of an object array. A typical FROM clause will contain the entity name being queried and assign it an alias. Caution should be used when doing this, as it can result in Cartesian products of the two table. The WHERE or ON clause should ensure the two objects are joined in some way. EclipseLink also allows for the fully qualified class name of the entity to be used (as of EclipseLink 2.4). The JOIN clause allows any of the objects relationships to be joined into the query so they can be used in the WHERE clause. JOIN does not mean the relationships will be fetched, unless the FETCH option is included. When used with a collection relationship you can join the same relationship multiple times to query multiple independent values. This avoids additional queries for each of the objects relationships, and ensures that the relationships have been fetched if they were LAZY. EclipseLink also supports batch fetching through query hints. ![]() Objects should normally always have the same data, no matter how they were queried, this is important for caching and consistency. This is only an issue if the alias is used in the WHERE clause on a collection relationship to filter the related objects that will be fetched.
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