ERROR: column is of type json but expression is of type character varying in Hibernate

Question

I need to map two columns of entity class as json in postgres using spring data jpa. After reading multiple stackoverflow posts and baeldung post ,

How to map a map JSON column to Java Object with JPA

https://www.baeldung.com/hibernate-persist-json-object

I did configuration as below. However, I am facing error "ERROR: column "headers" is of type json but expression is of type character varying"

Please provide some pointer to resolve this issue.

I have an entity class as below

@Entity
@Data
@SuperBuilder
@NoArgsConstructor
@AllArgsConstructor
public class Task {
    @Id
    @GeneratedValue(strategy = IDENTITY)
    private Integer id;
    
    private String url;
    private String httpMethod;

    @Convert(converter = HashMapConverter.class)
    @Column(columnDefinition = "json")
    private Map<String, String> headers;

    @Convert(converter = HashMapConverter.class)
    @Column(columnDefinition = "json")
    private Map<String, String> urlVariables;
}

I have created a test class to test if entity is persisted or not. On running this junit, below test case is failing with error as below

@SpringBootTest
class TaskRepositoryTest {

    private static Task randomTask = randomTask();

    @Autowired
    private TaskRepository taskRepository;

    @BeforeEach
    void setUp() {
        taskRepository.deleteAll();
        taskRepository.save(randomTask);
    }

    public static Task randomTask() {
        return randomTaskBuilder().build();
    }

    public static TaskBuilder randomTaskBuilder() {
        Map<String,String> headers = new HashMap<>();
        headers.put(randomAlphanumericString(10),randomAlphanumericString(10));

        Map<String,String> urlVariables = new HashMap<>();
        urlVariables.put(randomAlphanumericString(10),randomAlphanumericString(10));

        return builder()
                .id(randomPositiveInteger())
                .httpMethod(randomAlphanumericString(10))
                .headers(headers)
                .urlVariables(urlVariables)
                .url(randomAlphanumericString(10)));
    }
}

Using liquibase, I have created table in postgres DB and I could see column datatype as json.

databaseChangeLog:
  - changeSet:
      id: 1
      author: abc
      changes:
        - createTable:
            tableName: task
            columns:
              - column:
                  name: id
                  type: int
                  autoIncrement: true
                  constraints:
                    primaryKey: true
              - column:
                  name: url
                  type: varchar(250)
                  constraints:
                    nullable: false
                    unique: true
              - column:
                  name: http_method
                  type: varchar(50)
                  constraints:
                    nullable: false
              - column:
                  name: headers
                  type: json
              - column:
                  name: url_variables
                  type: json
      rollback:
        - dropTable:
            tableName: task

Answer 1

Above configuration did not work.

Hence, I followed below link to solve the use-case

https://vladmihalcea.com/how-to-map-json-objects-using-generic-hibernate-types/

"Provider com.fasterxml.jackson.module.jaxb.JaxbAnnotationModule not found" after Spring Boot Upgrade

Added additional dependencies in pom.xml

        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-jaxb-annotations</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vladmihalcea</groupId>
            <artifactId>hibernate-types-52</artifactId>
            <version>2.9.11</version>
        </dependency>

Removed HashMapConverter configuration and made below changes in entity class

@Entity
@Data
@SuperBuilder
@NoArgsConstructor
@AllArgsConstructor
@ToString(callSuper = true)
@TypeDefs({
        @TypeDef(name = "json", typeClass = JsonStringType.class),
        @TypeDef(name = "jsonb", typeClass = JsonBinaryType.class)
})
public class Task {
    @Id
    @GeneratedValue(strategy = IDENTITY)
    private Integer id;
    
    private String url;
    private String httpMethod;

    @Type(type = "jsonb")
    @Column(columnDefinition = "json")
    private Map<String, String> headers;

    @Type(type = "jsonb")
    @Column(columnDefinition = "json")
    private Map<String, String> urlVariables;
}

After these changes, TaskRepositoryTest passed.

Answer 2

I ran into this issue when I migrated my projects from MySQL 8.0.21 to Postgres 13. My project uses Spring boot with the Hibernate types dependency version 2.7.1. In my case the solution was simple.

All I needed to do was change that and it worked.

Referenced from the Hibernate Types Documentation page.

Answer 3

For anyone who landed here because they're using JdbcTemplate and getting this error, the solution is very simple: In your SQL statement, cast the JSON argument using ::jsonb.

E.g. String INSERT_SQL = "INSERT INTO xxx (id, json_column) VALUES(?, ?)"; becomes String INSERT_SQL = "INSERT INTO xxx (id, json_column) VALUES(?, ?::jsonb)";