[英]How to map a MySQL JSON column to a Java entity property using JPA and Hibernate
我將 MySQL 列聲明為JSON類型,並且在將其映射到 Jpa/Hibernate 時遇到問題。 我在后端使用 Spring Boot。
這是我的代碼的一小部分:
@Entity
@Table(name = "some_table_name")
public class MyCustomEntity implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@Column(name = "json_value")
private JSONArray jsonValue;
該程序返回一個錯誤並告訴我我無法映射該列。
在 mysql 表中,列定義為:
json_value JSON 非空;
我更喜歡這樣做:
代碼如下。
JsonToMapConverted.java
@Converter
public class JsonToMapConverter
implements AttributeConverter<String, Map<String, Object>>
{
private static final Logger LOGGER = LoggerFactory.getLogger(JsonToMapConverter.class);
@Override
@SuppressWarnings("unchecked")
public Map<String, Object> convertToDatabaseColumn(String attribute)
{
if (attribute == null) {
return new HashMap<>();
}
try
{
ObjectMapper objectMapper = new ObjectMapper();
return objectMapper.readValue(attribute, HashMap.class);
}
catch (IOException e) {
LOGGER.error("Convert error while trying to convert string(JSON) to map data structure.");
}
return new HashMap<>();
}
@Override
public String convertToEntityAttribute(Map<String, Object> dbData)
{
try
{
ObjectMapper objectMapper = new ObjectMapper();
return objectMapper.writeValueAsString(dbData);
}
catch (JsonProcessingException e)
{
LOGGER.error("Could not convert map to json string.");
return null;
}
}
}
域(實體映射)類的一部分
...
@Column(name = "meta_data", columnDefinition = "json")
@Convert(attributeName = "data", converter = JsonToMapConverter.class)
private Map<String, Object> metaData = new HashMap<>();
...
這個解決方案非常適合我。
您不必手動創建所有這些類型,您只需使用以下依賴項通過 Maven Central 獲取它們:
<dependency> <groupId>com.vladmihalcea</groupId> <artifactId>hibernate-types-52</artifactId> <version>${hibernate-types.version}</version> </dependency>
有關更多信息,請查看Hibernate Types 開源項目。
現在,解釋這一切是如何運作的。
假設您有以下實體:
@Entity(name = "Book")
@Table(name = "book")
@TypeDef(
name = "json",
typeClass = JsonType.class
)
public class Book {
@Id
@GeneratedValue
private Long id;
@NaturalId
private String isbn;
@Type(type = "json")
@Column(columnDefinition = "json")
private String properties;
//Getters and setters omitted for brevity
}
請注意上面代碼片段中的兩件事:
@TypeDef
用於定義一個新的自定義Hibernate類型, json
這是由處理JsonType
properties
屬性有一個json
列類型,它被映射為一個String
就是這樣!
現在,如果您保存實體:
Book book = new Book();
book.setIsbn("978-9730228236");
book.setProperties(
"{" +
" \"title\": \"High-Performance Java Persistence\"," +
" \"author\": \"Vlad Mihalcea\"," +
" \"publisher\": \"Amazon\"," +
" \"price\": 44.99" +
"}"
);
entityManager.persist(book);
Hibernate 將生成以下 SQL 語句:
INSERT INTO
book
(
isbn,
properties,
id
)
VALUES
(
'978-9730228236',
'{"title":"High-Performance Java Persistence","author":"Vlad Mihalcea","publisher":"Amazon","price":44.99}',
1
)
您還可以重新加載並修改它:
Book book = entityManager
.unwrap(Session.class)
.bySimpleNaturalId(Book.class)
.load("978-9730228236");
book.setProperties(
"{" +
" \"title\": \"High-Performance Java Persistence\"," +
" \"author\": \"Vlad Mihalcea\"," +
" \"publisher\": \"Amazon\"," +
" \"price\": 44.99," +
" \"url\": \"https://www.amazon.com/High-Performance-Java-Persistence-Vlad-Mihalcea/dp/973022823X/\"" +
"}"
);
Hibernate 為您處理UPDATE
語句:
SELECT b.id AS id1_0_
FROM book b
WHERE b.isbn = '978-9730228236'
SELECT b.id AS id1_0_0_ ,
b.isbn AS isbn2_0_0_ ,
b.properties AS properti3_0_0_
FROM book b
WHERE b.id = 1
UPDATE
book
SET
properties = '{"title":"High-Performance Java Persistence","author":"Vlad Mihalcea","publisher":"Amazon","price":44.99,"url":"https://www.amazon.com/High-Performance-Java-Persistence-Vlad-Mihalcea/dp/973022823X/"}'
WHERE
id = 1
GitHub 上提供的所有代碼。
如果您的 json 數組中的值是簡單的字符串,您可以這樣做:
@Type( type = "json" )
@Column( columnDefinition = "json" )
private String[] jsonValue;
Heril Muratovic 的回答很好,但我認為JsonToMapConverter
應該實現AttributeConverter<Map<String, Object>, String>
,而不是AttributeConverter<String, Map<String, Object>>
。 這是對我有用的代碼
@Slf4j
@Converter
public class JsonToMapConverter implements AttributeConverter<Map<String, Object>, String> {
@Override
@SuppressWarnings("unchecked")
public Map<String, Object> convertToEntityAttribute(String attribute) {
if (attribute == null) {
return new HashMap<>();
}
try {
ObjectMapper objectMapper = new ObjectMapper();
return objectMapper.readValue(attribute, HashMap.class);
} catch (IOException e) {
log.error("Convert error while trying to convert string(JSON) to map data structure.", e);
}
return new HashMap<>();
}
@Override
public String convertToDatabaseColumn(Map<String, Object> dbData) {
try {
ObjectMapper objectMapper = new ObjectMapper();
return objectMapper.writeValueAsString(dbData);
} catch (JsonProcessingException e) {
log.error("Could not convert map to json string.", e);
return null;
}
}
}
對於任何人都無法制作@J。 王回答工作:
嘗試添加此依賴項(適用於 hibernate 5.1 和 5.0,其他版本在此處檢查)
<dependency>
<groupId>com.vladmihalcea</groupId>
<artifactId>hibernate-types-5</artifactId>
<version>1.2.0</version>
</dependency>
並將這一行添加到實體
@TypeDef(name = "json", typeClass = JsonStringType.class)
實體類的完整版本:
@Entity
@Table(name = "some_table_name")
@TypeDef(name = "json", typeClass = JsonStringType.class)
public class MyCustomEntity implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@Type( type = "json" )
@Column( columnDefinition = "json" )
private List<String> jsonValue;
}
我使用 spring boot 1.5.9 和 hibernate-types-5 1.2.0 測試代碼。
在 Kotlin 中,上述建議的以下變化/組合對我有用:
@Entity
@Table(name = "product_menu")
@TypeDef(name = "json", typeClass = JsonStringType::class)
data class ProductMenu(
@Type(type = "json")
@Column(name = "menu_json", columnDefinition = "json")
@Convert(attributeName = "menuJson", converter = JsonToMapConverter::class)
val menuJson: HashMap<String, Any> = HashMap()
) : Serializable
import com.fasterxml.jackson.core.JsonProcessingException
import com.fasterxml.jackson.databind.ObjectMapper
import org.slf4j.LoggerFactory
import java.io.IOException
import javax.persistence.AttributeConverter
class JsonToMapConverter : AttributeConverter<String, HashMap<String, Any>> {
companion object {
private val LOGGER = LoggerFactory.getLogger(JsonToMapConverter::class.java)
}
override fun convertToDatabaseColumn(attribute: String?): HashMap<String, Any> {
if(attribute == null) {
return HashMap()
}
try {
val objectMapper = ObjectMapper()
@Suppress("UNCHECKED_CAST")
return objectMapper.readValue(attribute, HashMap::class.java) as HashMap<String, Any>
} catch (e: IOException) {
LOGGER.error("Convert error while trying to convert string(JSON) to map data structure.")
}
return HashMap()
}
override fun convertToEntityAttribute(dbData: HashMap<String, Any>?): String? {
return try {
val objectMapper = ObjectMapper()
objectMapper.writeValueAsString(dbData)
} catch (e: JsonProcessingException) {
LOGGER.error("Could not convert map to json string.")
return null
}
}
}
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