OrderBy (Java EE 5)

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SUMMARY: REQUIRED | OPTIONAL

DETAIL: ELEMENT

javax.persistence Annotation Type OrderBy

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

Implements: Annotation

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

此注释指定获取关联时，使用 Collection 定义了值的关联元素的排列顺序。

value 排序元素的语法为 orderby_list，如下所示：

orderby_list::= orderby_item [,orderby_item]*
orderby_item::= property_or_field_name [ASC | DESC]

如果没有指定 ASC 或 DESC，则假定为 ASC（升序）。

如果没有指定排序元素，则假定使用关联实体的主键进行排序。

属性或字段名称必须对应于关联类的持久属性或字段名称。排序中使用的属性或字段必须对应于支持比较运算符的列。

示例：
    
    @Entity public class Course {
     ...
     @ManyToMany
     @OrderBy("lastname ASC")
     public List getStudents() {...};
     ...
    }
    
    @Entity public class Student {
      ...
      @ManyToMany(mappedBy="students")
      @OrderBy // PK is assumed
      public List getCourses() {...};
      ...
    }

since

Java Persistence 1.0

英文文档：

This annotation specifies the ordering of the elements of a collection valued association at the point when the association is retrieved.

The syntax of the value ordering element is an orderby_list, as follows:

    orderby_list::= orderby_item [,orderby_item]*
    orderby_item::= property_or_field_name [ASC | DESC]

If ASC or DESC is not specified, ASC (ascending order) is assumed.

If the ordering element is not specified, ordering by the primary key of the associated entity is assumed.

The property or field name must correspond to that of a persistent property or field of the associated class. The properties or fields used in the ordering must correspond to columns for which comparison operators are supported.

    Example:
    
    @Entity public class Course {
     ...
     @ManyToMany
     @OrderBy("lastname ASC")
     public List getStudents() {...};
     ...
    }
    
    @Entity public class Student {
      ...
      @ManyToMany(mappedBy="students")
      @OrderBy // PK is assumed
      public List getCourses() {...};
      ...
    }

Since:: Java Persistence 1.0

Optional Element Summary
`String`	`value` An `orderby_list`, specified as follows: orderby_list::= orderby_item [,orderby_item]* orderby_item::= property_or_field_name [ASC \| DESC] If `ASC` or `DESC` is not specified, `ASC` (ascending order) is assumed.

abstract public String value()
orderby_list，指定如下：

orderby_list::= orderby_item [,orderby_item]*
orderby_item::= property_or_field_name [ASC | DESC]