FetchType (Java EE 5)

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javax.persistence Enum FetchType

java.lang.Object
  java.lang.Enum<FetchType>
      javax.persistence.FetchType

All Implemented Interfaces:: Serializable, Comparable<FetchType>

public enum FetchType
extends Enum<FetchType>

Extends: Enum<E>

定义从数据库获取数据的战略。EAGER 战略是必须立即获取数据的持久性提供者运行时的要求。LAZY 战略是第一次访问时应该延迟获取值的持久性提供者运行时的提示。对于指定了 LAZY 战略提示的实现，允许其立即获取数据。需要特别指出的是，延迟获取可能仅对使用基于属性访问的 Basic 映射可用。

示例：
   @Basic(fetch=LAZY)
   protected String getName() { return name; }

since

Java Persistence 1.0

英文文档：

Defines strategies for fetching data from the database. The EAGER strategy is a requirement on the persistence provider runtime that data must be eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime that data should be fetched lazily when it is first accessed. The implementation is permitted to eagerly fetch data for which the LAZY strategy hint has been specified. In particular, lazy fetching might only be available for Basic mappings for which property-based access is used.

   Example:
   @Basic(fetch=LAZY)
   protected String getName() { return name; }

Since:: Java Persistence 1.0

Enum Constant Summary
`EAGER` Defines that data must be eagerly fetched
`LAZY` Defines that data can be lazily fetched

Method Summary
`static FetchType`	`valueOf(String name)` Returns the enum constant of this type with the specified name.
`static FetchType[]`	`values()` Returns an array containing the constants of this enum type, in the order they're declared.

Methods inherited from class java.lang.Enum
`clone, compareTo, equals, getDeclaringClass, hashCode, name, ordinal, toString, valueOf`

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, wait, wait, wait`

Enum Constant Detail

英文文档：

LAZY

public static final FetchType LAZY

Defines that data can be lazily fetched

英文文档：

EAGER

public static final FetchType EAGER

Defines that data must be eagerly fetched

Method Detail

final public static FetchType[] values()

英文文档：
values

public static final FetchType[] values()

Returns an array containing the constants of this enum type, in the order they're declared. This method may be used to iterate over the constants as follows:

for(FetchType c : FetchType.values())
        System.out.println(c);

Returns:: an array containing the constants of this enum type, in the order they're declared

public static FetchType valueOf(String name)

英文文档：
valueOf

public static FetchType valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (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 type has no constant with the specified name