Basic (Java EE 5 SDK)

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Java EE 5 SDK

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摘要: REQUIRED | OPTIONAL

详细信息: ELEMENT

javax.persistence Annotation Type Basic

@Target(value={METHOD,FIELD}) @Retention(value=RUNTIME) public @interface Basic

The Basic annotation is the simplest type of mapping to a database column. The Basic annotation can be applied to a persistent property or instance variable of any of the following types: Java primitive types, wrappers of the primitive types, String, java.math.BigInteger, java.math.BigDecimal, java.util.Date, java.util.Calendar, java.sql.Date, java.sql.Time, java.sql.Timestamp, byte[], Byte[], char[], Character[], enums, and any other type that implements Serializable.

The use of the Basic annotation is optional for persistent fields and properties of these types.

从以下版本开始:: Java Persistence 1.0

Optional Element Summary
`FetchType`	`fetch` (Optional) Defines whether the value of the field or property should be lazily loaded or must be eagerly fetched.
`boolean`	`optional` (Optional) Defines whether the value of the field or property may be null.

fetch

public abstract FetchType fetch

(Optional) Defines whether the value of the field or property should be lazily loaded or must be eagerly fetched. The EAGER strategy is a requirement on the persistence provider runtime that the value must be eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime. If not specified, defaults to EAGER.

默认值:: EAGER

optional

public abstract boolean optional

(Optional) Defines whether the value of the field or property may be null. This is a hint and is disregarded for primitive types; it may be used in schema generation. If not specified, defaults to true.

默认值:: true

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