Enum Class FetchMode
- All Implemented Interfaces:
Serializable
,Comparable<FetchMode>
,Constable
The JPA-defined FetchType
enumerates the
possibilities for when an association might be fetched. This
annotation defines how it is fetched in terms of the actual
SQL executed by the database.
- See Also:
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Nested Class Summary
Nested classes/interfaces inherited from class java.lang.Enum
Enum.EnumDesc<E extends Enum<E>>
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Enum Constant Summary
Enum ConstantDescriptionUse an outer join to load all instances of the related entity or collection at once, as part of the execution of a query.Use a secondary select to load a single associated entity or collection, at some point after an initial query is executed.Use a secondary select with a subselect that re-executes an initial query to load all instances of the related entity or collection at once, at some point after the initial query is executed. -
Method Summary
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Enum Constant Details
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SELECT
Use a secondary select to load a single associated entity or collection, at some point after an initial query is executed.This is the default fetching strategy for any association or collection in Hibernate, unless the association or collection is explicitly marked for eager fetching.
This fetching strategy is vulnerable to the "N+1 selects" bugbear, though the impact may be alleviated somewhat via:
- enabling batch fetching using
BatchSize
, or - ensuring that the associated entity or collection may be retrieved from the second-level cache.
This fetching strategy is, in principle, compatible with both eager and lazy fetching. On the other hand, performance considerations dictate that it should only be used in combination wih
EAGER
fetching when it is almost certain that the associated data will be available in the second-level cache. - enabling batch fetching using
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JOIN
Use an outer join to load all instances of the related entity or collection at once, as part of the execution of a query. No subsequent queries are executed.This is the default fetching strategy for an association or collection that is explicitly marked for eager fetching.
This fetching strategy is incompatible with lazy fetching since the associated data is retrieved as part of the initial query.
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SUBSELECT
Use a secondary select with a subselect that re-executes an initial query to load all instances of the related entity or collection at once, at some point after the initial query is executed. This fetching strategy is currently only available for collections and many-valued associations.This advanced fetching strategy is compatible with both eager and lazy fetching.
Subselect fetching may be contrasted with batch fetching:
- In batch fetching, a list of primary key values is sent to
the database, bound within a SQL
in
condition. - In subselect fetching, the primary keys are determined by re-execution of the initial query within a SQL subselect.
- In batch fetching, a list of primary key values is sent to
the database, bound within a SQL
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Method Details
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values
Returns an array containing the constants of this enum class, in the order they are declared.- Returns:
- an array containing the constants of this enum class, in the order they are declared
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valueOf
Returns the enum constant of this class with the specified name. The string must match exactly an identifier used to declare an enum constant in this class. (Extraneous whitespace characters are not permitted.)- Parameters:
name
- the name of the enum constant to be returned.- Returns:
- the enum constant with the specified name
- Throws:
IllegalArgumentException
- if this enum class has no constant with the specified nameNullPointerException
- if the argument is null
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getHibernateFetchMode
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