Hibernate mapping to store custom object as a String-CodePudding

I'm trying to create mapping that will store my custom object as a String to a single column in a database table.

Article.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<>() { /* */ };
    }

}

When Hibernate tries to create the database, I get this one:

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

I don't want to use @ElementCollection as this would create additional table in my database.

Next try was to change mapping to this:

Article.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<>() { /* */ };
    }

}

In second case I had to remove description property from entity because database column gets a name data which is a name of Map inside LocalizedField class.

In the final I would like to have more than one LocalizedField property handled by the same @Converter (of course, if possible).

But in cotrary to first attempt, at least I get column stored as expected, in JSON format but it's named data instead of 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"
}

What did I do wrong?

CodePudding user response：

Just drop @Embedded, @Embeddable, and attributeName from the original solution:

@Entity
public class Article {

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

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

}

@Getter @Setter
public class LocalizedField {

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

}

@Embedded and @AttributeConverter are mutually exclusive. You're getting a MappingException because Hibernate cannot figure out how the hell it's supposed to map LocalizedField as an embeddable, since data itself doesn't have an attribute converter.

CodePudding user response：

The solution that works with more than one LocalizedField properties needs use of @AttributeOverride.

Changes are:

Article.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<>();