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

Question

We have a big table with a lot of columns. After we moved to MySQL Cluster, the table cannot be created because of:

ERROR 1118 (42000): Row size too l

Answer 1

I had a similar problem, and solved it by using @Externalizer annotation and Jackson to serialize/deserialize data (@Externalizer is OpenJPA-specific annotation, so you have to check with your JPA implementation similar possibility).

@Persistent
@Column(name = "params")
@Externalizer("toJSON")
private Params params;

Params class implementation:

public class Params {
    private static final ObjectMapper mapper = new ObjectMapper();

    private Map map;

    public Params () {
        this.map = new HashMap();
    }

    public Params (Params another) {
        this.map = new HashMap();
        this.map.putAll(anotherHolder.map);
    }

    public Params(String string) {
        try {
            TypeReference> typeRef = new TypeReference>() {
            };
            if (string == null) {
                this.map = new HashMap();
            } else {
                this.map = mapper.readValue(string, typeRef);
            }
        } catch (IOException e) {
            throw new PersistenceException(e);
        }
    }

    public String toJSON() throws PersistenceException {
        try {
            return mapper.writeValueAsString(this.map);
        } catch (IOException e) {
            throw new PersistenceException(e);
        }
    }

    public boolean containsKey(String key) {
        return this.map.containsKey(key);
    }

    // Hash map methods
    public Object get(String key) {
        return this.map.get(key);
    }

    public Object put(String key, Object value) {
        return this.map.put(key, value);
    }

    public void remove(String key) {
        this.map.remove(key);
    }

    public Object size() {
        return map.size();
    }
}

HTH