如何通过JPQL访问JPA中的“地图"字段 [英] How to access Map field in JPA via JPQL

问题描述

例如，如果有一个@ElementCollection文件具有Map类型，那么如果我尝试获取map键或value字段，该如何处理?

for example, if there is an @ElementCollection file which is with a Map type, then if I try to get the map key or value field then how to process?

Class Deal{
.....

private String name;

private String department;

private DealType type;

@AttributeOverrides({
    @AttributeOverride(name="value.in.available", column=@Column(name="in_avl")),
    @AttributeOverride(name="value.in.unavailable", column=@Column(name="in_unv")),
    @AttributeOverride(name="value.out.available", column=@Column(name="out_avl")),
    @AttributeOverride(name="value.out.unavailable", column=@Column(name="out_unv"))
})
@ElementCollection(fetch = FetchType.EAGER)
    ......
}

所以，如果我尝试得到类似的东西

So if I try to get something like this

select new SummaryAmount(SUM(t.value.in.available), SUM(t.value.in.unavailable),
SUM(t.value.out.available), SUM(t.value.out.unavailable)) from Deal AS d INNER 
JOIN d.transactionAmounts t GROUP by t.key;

现在有可能解决吗?除了我发明了t.value和t.key之外，其他所有内容都遵循本书，因为我真的不知道如何在JPQL中显示映射键和值.谢谢

Is it something possible can work out now? Everything is follow the book except I invent the t.value and t.key as I really don't know how to present map key and value in JPQL.Thanks

谢谢

推荐答案

尝试一下:

SELECT new SummaryAmount(SUM(VALUE(t).in.available), SUM(VALUE(t)in.unavailable),
SUM(VALUE(t).out.available), SUM(VALUE(t).out.unavailable)) from Deal AS d INNER 
JOIN d.transactionAmounts t GROUP by KEY(t);

现在摘录自JPA规范:

And now an excerpt from the JPA specification:

由KEY，VALUE或ENTRY限定的标识变量 运算符是路径表达式. KEY，VALUE和ENTRY运算子可以 仅适用于与 地图值关联或地图值元素集合.的类型 路径表达式是根据 手术;也就是说，该字段的抽象架构类型为 KEY，VALUE或ENTRY运算符的值(地图键，地图值或 分别输入地图).[53]

An identification variable qualified by the KEY, VALUE, or ENTRY operator is a path expression. The KEY, VALUE, and ENTRY operators may only be applied to identification variables that correspond to map-valued associations or map-valued element collections. The type of the path expression is the type computed as the result of the operation; that is, the abstract schema type of the field that is the value of the KEY, VALUE, or ENTRY operator (the map key, map value, or map entry respectively).[53]

合格标识变量的语法如下.

The syntax for qualified identification variables is as follows.

qualified_identification_variable :: =

qualified_identification_variable :: =

KEY (identification_variable)|

KEY(identification_variable) |

VALUE (identification_variable)|

VALUE(identification_variable) |

ENTRY (identification_variable)

ENTRY(identification_variable)

使用KEY或VALUE运算符的路径表达式可以更进一步 组成.使用ENTRY运算符的路径表达式是terminal.它 不能进一步构成，只能出现在列表的SELECT列表中 查询.

A path expression using the KEY or VALUE operator can be further composed. A path expression using the ENTRY operator is terminal. It cannot be further composed and can only appear in the SELECT list of a query.

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