Column (Java EE 5)

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

用于指定持久属性或字段的映射列。如果没有指定 Column 注释，则应用默认值。

示例：

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

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

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

 

since

en Java Persistence 1.0

英文文档：

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; }

 

Since:

Java Persistence 1.0

---

Optional Element Summary
String	columnDefinition           (Optional) The SQL fragment that is used when generating the DDL for the column.
boolean	insertable           (Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
int	length           (Optional) The column length.
String	name           (Optional) The name of the column.
boolean	nullable           (Optional) Whether the database column is nullable.
int	precision           (Optional) The precision for a decimal (exact numeric) column.
int	scale           (Optional) The scale for a decimal (exact numeric) column.
String	table           (Optional) The name of the table that contains the column.
boolean	unique           (Optional) Whether the property is a unique key.
boolean	updatable           (Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.

 

abstract public String name()
（可选）列名称。默认为属性或字段名称。

英文文档：

name

public abstract String name

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

Default:

""

---

abstract public boolean unique()
（可选）属性是否为唯一键。这是表格级别的 UniqueConstraint 注释的快捷方式，在唯一的键约束只有一个字段时很有用。除了应用在表格级别指定的约束条件和主键映射引起的约束条件外，还应用此约束条件。

英文文档：

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.

Default:

false

---

abstract public boolean nullable()
（可选）数据库列是否可以为 null。

英文文档：

nullable

public abstract boolean nullable

(Optional) Whether the database column is nullable.

Default:

true

---

abstract public boolean insertable()
（可选）持久性提供者生成的 SQL INSERT 语句中是否包含该列。

英文文档：

insertable

public abstract boolean insertable

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

Default:

true

---

abstract public boolean updatable()
（可选）持久性提供者生成的 SQL UPDATE 语句中是否包含该列。

英文文档：

updatable

public abstract boolean updatable

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

Default:

true

---

abstract public String columnDefinition()
（可选）生成该列的 DDL 时使用的 SQL 句段。

默认为生成的 SQL，以创建推断类型的列。

英文文档：

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.

Default:

""

---

abstract public String table()
（可选）包含该列的表格名称。如果不存在，则假设该列位于主表格中。

英文文档：

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.

Default:

""

---

abstract public int length()
（可选）列长。（只在使用值为字符串的列时应用。）

英文文档：

length

public abstract int length

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

Default:

255

---

abstract public int precision()
（可选）十进制（精确数字）列的精度。（只在使用十进制列时应用。）如果在生成此列的 DDL 时使用，则开发人员必须设置此值。

英文文档：

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.

Default:

0

---

abstract public int scale()
（可选）十进制（精确数字）列的小数位数。（只在使用十进制列时应用。）

英文文档：

scale

public abstract int scale

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

Default:

0

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