Hibernate 映射以将自定义 object 存储为字符串

Question

我正在尝试创建映射，它将我的自定义 object 作为字符串存储到数据库表中的单个列。

文章.java

@Entity
public class Article {

    @Getter @Setter
    @Embedded
    @Column(name = "name", columnDefinition = "TEXT")
    @Convert(converter = LocalizedFieldConverter.class,
        attributeName = "name")
    private LocalizedField name = new LocalizedField();

    @Getter @Setter
    @Embedded
    @Column(name = "name", columnDefinition = "TEXT")
    @Convert(converter = LocalizedFieldConverter.class,
        attributeName = "description")
    private LocalizedField description = new LocalizedField();

}

LocalizedField.java

@Embeddable @Getter @Setter
public class LocalizedField {

    // map key is "en-US", value is a translation
    private Map<String, String> data = new HashMap<>();

}

LocalizedFieldConverter.java

@Converter
public class LocalizedFieldConverter
    implements AttributeConverter<LocalizedField, String>, Serializable
{

    @Override
    public String convertToDatabaseColumn(LocalizedField attribute) {
        if (attribute == null) { return null; }
        try {
            return new ObjectMapper().writeValueAsString(attribute);
        }
        catch (JsonProcessingException e) { return null; }
    }

    @Override
    public LocalizedField convertToEntityAttribute(String dbData) {
        if (dbData == null) { return null; }
        try {
            return new ObjectMapper().readValue(dbData, typeReference());
        }
        catch (JsonProcessingException e) { return null; }
    }

    private static final TypeReference<LocalizedField> typeReference() {
        return new TypeReference<>() { /* */ };
    }

}

当 Hibernate 尝试创建数据库时，我得到了这个：

Caused by: org.hibernate.MappingException: Could not determine type for: java.util.Map, at table: article, for columns: [org.hibernate.mapping.Column(data)]

我不想使用@ElementCollection ，因为这会在我的数据库中创建额外的表。

---

接下来的尝试是将映射更改为：

文章.java

@Getter @Setter
private LocalizedField name = new LocalizedField();

LocalizedField.java

@Convert(converter = LocalizedFieldMapConverter.class)
private Map<String, String> data = new HashMap<>();

LocalizedFieldMapConverter.java

@Converter
public class LocalizedFieldMapConverter
    implements AttributeConverter<Map<String, String>, String>, Serializable {

    @Override
    public String convertToDatabaseColumn(Map<String, String> attribute) {
        if (attribute == null) { return null; }
        try {
            return new ObjectMapper().writeValueAsString(attribute);
        }
        catch (JsonProcessingException e) { return null; }
    }

    @Override
    public Map<String, String> convertToEntityAttribute(String dbData) {
        if (dbData == null) { return null; }
        try {
            return new ObjectMapper().readValue(dbData, typeReference());
        }
        catch (JsonProcessingException e) { return null; }
    }

    private static final TypeReference<Map<String, String>> typeReference() {
        return new TypeReference<>() { /* */ };
    }

}

在第二种情况下，我必须从实体中删除description属性，因为数据库列获取名称data ，它是LocalizedField class 内的 Map 的名称。

最后，我希望有多个LocalizedField属性由同一个@Converter处理（当然，如果可能的话）。

但与第一次尝试相反，至少我得到了按预期存储的列，格式为 JSON ，但它被命名为data而不是name ：

{
    "hr-HR" : "Sončnica & vitamin E šampon za kosu i tijelo 1000 ml",
    "en-US" : "Sunflower & Vitamin E Hair & Body Shampoo 1000 ml",
    "sr-RS" : "Сончница & витамин Е шампон за косу и тело 1000 мл"
}

我做错了什么？

Answer 1

只需从原始解决方案中删除@Embedded 、 @Embeddable和attributeName ：

@Entity
public class Article {

    @Getter @Setter
    @Column(columnDefinition = "TEXT")
    private LocalizedField name = new LocalizedField();

    @Getter @Setter
    @Column(columnDefinition = "TEXT")
    private LocalizedField description = new LocalizedField();

}

@Getter @Setter
public class LocalizedField {

    private Map<String, String> data = new HashMap<>();

}

@Converter(autoApply=true)
public class LocalizedFieldConverter { ... }

@Embedded和@AttributeConverter是互斥的。 您收到MappingException是因为 Hibernate 无法弄清楚它应该如何将 map LocalizedField作为可嵌入对象，因为data本身没有属性转换器。

编辑由于您的AttributeConverter适用于LocalizedField ，而不是直接适用于AttributeConverter.data ，您需要：

@Converter
public class LocalizedFieldMapConverter
    implements AttributeConverter<LocalizedField, String>, Serializable {

    @Override
    public String convertToDatabaseColumn(LocalizedField attribute) {
        if (attribute == null) { return null; }
        try {
            return new ObjectMapper().writeValueAsString(attribute.getData());
        }
        catch (JsonProcessingException e) { return null; }
    }

    @Override
    public LocalizedField convertToEntityAttribute(String dbData) {
        if (dbData == null) { return null; }
        try {
            Map<String, String> data = new ObjectMapper().readValue(dbData, typeReference());
LocalizedField result = new LocalizedField();
result.setData(data); // or add an @AllArgsConstructor and use it
return result;
        }
        catch (JsonProcessingException e) { return null; }
    }

    private static final TypeReference<Map<String, String>> typeReference() {
        return new TypeReference<>() { /* */ };
    }

}

或者，如果您不需要额外的LocalizedField class 用于任何其他目的，只需使用：

@Entity
public class Article {

    @Getter @Setter
    @Column(columnDefinition = "TEXT")
    @Convert(converter = LocalizedFieldConverter.class)
    private Map<String, String> name = new HashMap<>();

    @Getter @Setter
    @Column(columnDefinition = "TEXT")
    @Convert(converter = LocalizedFieldConverter.class)
    private Map<String, String> description = new HashMap<>();

}

Answer 2

使用多个 LocalizedField 属性的解决方案需要使用@AttributeOverride 。

变化是：

文章.java

@Getter @Setter
@Embedded
@AttributeOverride(
    name = "data", // refers to Map name inside LocalizedField
    column = @Column(
        name = "name", // column name to use for converted LocalizedField
        columnDefinition = "TEXT"
    )
)
private LocalizedField name = new LocalizedField();

@Getter @Setter
@Embedded
@AttributeOverride(
    name = "data", // refers to Map name inside LocalizedField
    column = @Column(
        name = "description", // column name to use for converted LocalizedField
        columnDefinition = "TEXT"
    )
)
private LocalizedField description = new LocalizedField();

LocalizedField.java

@Convert(converter = LocalizedFieldMapConverter.class)
private Map<String, String> data = new HashMap<>();