Column (Java EE 5 SDK)

javax.persistence Annotation Type Column

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

Is used to specify a mapped column for a persistent property or field. If no Column annotation is specified, the default values are applied.

Examples:

 Example 1:
 @Column(name="DESC", nullable=false, length=512)
 public String getDescription() { return description; }

 Example 2:
 @Column(name="DESC",
         columnDefinition="CLOB NOT NULL",
         table="EMP_DETAIL")
 @Lob
 public String getDescription() { return description; }

 Example 3:
 @Column(name="ORDER_COST", updatable=false, precision=12, scale=2)
 public BigDecimal getCost() { return cost; }

 

从以下版本开始:

Java Persistence 1.0

name

public abstract String name

(Optional) The name of the column. Defaults to the property or field name.

默认值:

""

unique

public abstract boolean unique

(Optional) Whether the property is a unique key. This is a shortcut for the UniqueConstraint annotation at the table level and is useful for when the unique key constraint is only a single field. This constraint applies in addition to any constraint entailed by primary key mapping and to constraints specified at the table level.

默认值:

false

nullable

public abstract boolean nullable

(Optional) Whether the database column is nullable.

默认值:

true

insertable

public abstract boolean insertable

(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.

默认值:

true

updatable

public abstract boolean updatable

(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.

默认值:

true

columnDefinition

public abstract String columnDefinition

(Optional) The SQL fragment that is used when generating the DDL for the column.

Defaults to the generated SQL to create a column of the inferred type.

默认值:

""

table

public abstract String table

(Optional) The name of the table that contains the column. If absent the column is assumed to be in the primary table.

默认值:

""

length

public abstract int length

(Optional) The column length. (Applies only if a string-valued column is used.)

默认值:

255

precision

public abstract int precision

(Optional) The precision for a decimal (exact numeric) column. (Applies only if a decimal column is used.) Value must be set by developer if used when generating the DDL for the column.

默认值:

0

scale

public abstract int scale

(Optional) The scale for a decimal (exact numeric) column. (Applies only if a decimal column is used.)

默认值:

0

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