使用 Spring Data JPA 自动转换参数 [英] Automatically convert a parameter with Spring Data JPA
问题描述
在我们的实体 bean 中,我们使用自定义 ID 格式,其中包括校验和来验证 ID 是否实际有效.Id 看起来像 ID827391738979
.为了确保所有代码只使用正确的 ID,我们围绕 ID 字符串创建了一个代码包装器:
In our entity beans we use a custom ID format which includes a checksum to verify that the ID is actually valid. Ids look like ID827391738979
. To make sure that all code uses correct IDs only we created a code wrapper around an ID String:
class ID {
public ID(String id) {
// parse and verify ID
}
public String toString() {
return id;
}
}
所有代码只使用这个 ID
对象.但是在我们的实体中,我们将 ID 定义为 String
:
All code just uses this ID
object. However in our entity we have defined the ID as a String
:
class SomeEntity {
@Column
private String itsID;
}
现在我们想使用 Spring-Data-JPA 通过它的 id 查询某个对象.所以我们这样做:
Now we want to use Spring-Data-JPA to query some object by it's id. So we do:
public SomeEntity findByItsID(ID itsId);
问题是,现在 Spring Data JPA 尝试将 ID 类型的参数分配给查询,而查询当然需要 String
.
Problem is, that now Spring Data JPA tries to assign the ID-typed parameter to the query, while the query of course expects a String
.
在将参数插入查询之前,是否可以让 Spring Data JPA 将参数转换为预期类型(例如,通过注册 Spring 转换器)?或者,我们是否必须让方法采用这样的字符串:
Is it possible to have Spring Data JPA convert the parameter to the expected type (e.g. by registering a Spring converter) before it is inserted into the query? Or, do we have to let the method take a String like this:
public SomeEntity findByItsId(String itsId);
我宁愿避免这种情况,因此所有代码都可以使用 ID
类而不是诉诸字符串.
I would rather avoid this, so all code can use the ID
class instead of resorting to Strings.
推荐答案
您可以在带有 JPA 2.1 的实体中使用 自定义类型 @Convert
,因此 JPA 为您进行了转换(我也使用 Spring Data JPA 对其进行了测试,并且透明地工作!),请参阅:
You could use a custom type in your entity with JPA 2.1 @Convert
, so JPA makes the conversion for you (I've tested it with Spring Data JPA also, and it worked transparently!), see:
实体:
@Entity
class SomeEntity {
@Column(name = "my_id_column_name")
@Convert(converter = MyIDConverter.class)
private ID itsID;
}
转换器:
public class MyIDConverter implements AttributeConverter<ID, String> {
@Override
public String convertToDatabaseColumn(ItStaticDataKey javaKey) {
// your implementation here
}
@Override
public ItStaticDataKey convertToEntityAttribute(final String databaseKey) {
// your implementation here
}
}
注意事项:
- 确保您使用的是兼容 JPA-2.1 的 Spring Data JPA 版本.(我确信 Spring Data JPA 1.7.0(及更高版本)是(或至少应该)兼容的.
- 很遗憾,如果该字段也应使用
@Id
进行注释,则该方法将不起作用. - 如果您使用 EclipseLink,则必须在 persistence.xml 中定义转换器,否则它不会选择它.https://bugs.eclipse.org/bugs/show_bug.cgi?id=412454.
- 在 Spring 上使用 JPA,包含转换器的包必须出现在
EntityManagerFactoryBean
上的属性packageToScan
中.
- Make sure you're using a JPA-2.1-compatible Spring Data JPA version. (I'm sure that Spring Data JPA 1.7.0 (and above) are (or at least should) be compatible).
- Unfortunately, it won't work if that field should also be annotated with
@Id
. - If you use EclipseLink, you have to define converter in persistence.xml, or it doesn't pick it up. https://bugs.eclipse.org/bugs/show_bug.cgi?id=412454.
- With JPA on Spring, package containing converters have to appear in property
packageToScan
onEntityManagerFactoryBean
.
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