Java 使用 Spring Data JPA 自动转换参数
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Automatically convert a parameter with Spring Data JPA
提问by Jan Thom?
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:
在我们的实体 bean 中，我们使用包含校验和的自定义 ID 格式来验证 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：
class ID {
public ID(String id) {
// parse and verify ID
}
public String toString() {
return id;
}
}
All code just uses this IDobject. However in our entity we have defined the ID as a String:
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 a String：
class SomeEntity {
@Column
private String itsID;
}
Now we want to use Spring-Data-JPA to query some object by it's id. So we do:
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：
public SomeEntity findByItsID(ID itsId);
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.
问题是，现在 Spring Data JPA 尝试将 ID 类型的参数分配给查询，而查询当然需要一个String.
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:
是否可以在将参数插入查询之前让 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，我们是否必须让该方法采用这样的字符串：
public SomeEntity findByItsId(String itsId);
I would rather avoid this, so all code can use the IDclass instead of resorting to Strings.
我宁愿避免这种情况，因此所有代码都可以使用ID该类而不是诉诸字符串。
采纳答案by falsarella
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:
您可以在带有 JPA 2.1 的实体中@Convert使用自定义类型，因此 JPA 为您进行转换（我也使用 Spring Data JPA 对其进行了测试，并且它透明地工作！），请参阅：
Entity:
实体：
@Entity
class SomeEntity {
@Column(name = "my_id_column_name")
@Convert(converter = MyIDConverter.class)
private ID itsID;
}
Converter:
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
}
}
Notes:
笔记：
- 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
packageToScanonEntityManagerFactoryBean.
- 确保您使用的是兼容 JPA-2.1 的 Spring Data JPA 版本。（我确定 Spring Data JPA 1.7.0（及更高版本）是（或至少应该）兼容的）。
- 不幸的是，如果该字段也应该用
@Id. - 如果使用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。
- 随着JPA春，包含转换器必须出现在属性
packageToScan上EntityManagerFactoryBean。
