Question

我在Hibernate中有类似下面的模型：

class Person {
    String name;
    List<Address> addresses;
}

class Address {
    String street;
    String city;
}

我现在想要将Person持久化到一个表，其中所有人的地址都被序列化为JSON字符串并存储在Person表的列中。数据库中的Person记录如下所示：

name: 'Benjamin Franklin', addresses: '[{"street"="...","city"="..."}, {...}]'

有没有办法使用Hibernate实现这个目标？

如果地址不是列表，我可以注册UserType来执行序列化。

我也不能使用JPA的@Converter，因为Hibernate实现不会检测到更改，请参阅HHH-10111。

Answer 1

您可以创建自定义类型：

import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.hibernate.HibernateException;
import org.hibernate.engine.spi.SessionImplementor;
import org.hibernate.usertype.DynamicParameterizedType;
import org.hibernate.usertype.UserType;

import java.io.IOException;
import java.io.Serializable;
import java.io.StringWriter;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Types;
import java.util.*;

public class JsonListType implements UserType, DynamicParameterizedType {

    private static final int[] SQL_TYPES = new int[]{Types.LONGVARCHAR};
    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

    private JavaType valueType = null;
    private Class<?> classType = null;

    @Override
    public int[] sqlTypes() {
        return SQL_TYPES;
    }

    @Override
    public Class<?> returnedClass() {
        return classType;
    }

    @Override
    public boolean equals(Object x, Object y) throws HibernateException {
        return Objects.equals(x, y);
    }

    @Override
    public int hashCode(Object x) throws HibernateException {
        return Objects.hashCode(x);
    }

    @Override
    public Object nullSafeGet(ResultSet rs, String[] names, SessionImplementor session, Object owner) throws HibernateException, SQLException {
        return nullSafeGet(rs, names, owner);
    }

    @Override
    public void nullSafeSet(PreparedStatement st, Object value, int index, SessionImplementor session) throws HibernateException, SQLException {
        nullSafeSet(st, value, index);
    }

    public Object nullSafeGet(ResultSet rs, String[] names, Object owner) throws HibernateException, SQLException {
        String value = rs.getString(names[0]);
        Object result = null;
        if (valueType == null) {
            throw new HibernateException("Value type not set.");
        }
        if (value != null && !value.equals("")) {
            try {
                result = OBJECT_MAPPER.readValue(value, valueType);
            } catch (IOException e) {
                throw new HibernateException("Exception deserializing value " + value, e);
            }
        }
        return result;
    }

    public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException {
        StringWriter sw = new StringWriter();
        if (value == null) {
            st.setNull(index, Types.VARCHAR);
        } else {
            try {
                OBJECT_MAPPER.writeValue(sw, value);
                st.setString(index, sw.toString());
            } catch (IOException e) {
                throw new HibernateException("Exception serializing value " + value, e);
            }
        }
    }

    @Override
    public Object deepCopy(Object value) throws HibernateException {
        if (value == null) {
            return null;
        } else if (valueType.isCollectionLikeType()) {
            try {
                Object newValue = value.getClass().newInstance();
                Collection newValueCollection = (Collection) newValue;
                newValueCollection.addAll((Collection) value);
                return newValueCollection;
            } catch (InstantiationException e) {
                throw new HibernateException("Failed to deep copy the collection-like value object.", e);
            } catch (IllegalAccessException e) {
                throw new HibernateException("Failed to deep copy the collection-like value object.", e);
            }
        }

        return null;
    }

    @Override
    public boolean isMutable() {
        return true;
    }

    @Override
    public Serializable disassemble(Object value) throws HibernateException {
        return (Serializable) deepCopy(value);
    }

    @Override
    public Object assemble(Serializable cached, Object owner) throws HibernateException {
        return deepCopy(cached);
    }

    @Override
    public Object replace(Object original, Object target, Object owner) throws HibernateException {
        return deepCopy(original);
    }

    @Override
    public void setParameterValues(Properties parameters) {
        try {

            // Get entity class
            Class<?> entityClass = Class.forName(parameters.getProperty(DynamicParameterizedType.ENTITY));
            Field property = null;

            // Find the field
            while(property == null && entityClass != null){
                try {
                    property = entityClass.getDeclaredField(parameters.getProperty(DynamicParameterizedType.PROPERTY));
                } catch (NoSuchFieldException e) {
                    entityClass = entityClass.getSuperclass();
                }
            }

            if(property != null){
                ParameterizedType listType = (ParameterizedType) property.getGenericType();
                Class<?> listClass = (Class<?>) listType.getActualTypeArguments()[0];
                valueType = OBJECT_MAPPER.getTypeFactory().constructCollectionType(ArrayList.class, listClass);
                classType = List.class;
            }

        } catch (ClassNotFoundException e) {
            throw new IllegalArgumentException(e);
        }
    }

}

并像这样使用它：

@Type(type = "com.company.util.JsonListType")
private List<MyCustomClass> myCustomClasses;

此解决方案不是特定于数据库的，您可以轻松扩展它以支持地图和自定义可复制实体。

Answer 2

我没有尝试过自己，但这里有一篇值得参考的博客...... https://dzone.com/articles/annotating-custom-types

这基本上建议您添加自定义注释。例如，带注释的类称为“AddressJSONParser”，应将您的Address对象转换为JSON（使用解析器）并返回String。您还应该考虑使用一个反向解析器，从JSON字符串返回到Address对象...

使用Hibernate在文本字段中将List <someclass>存储为JSON

2 个答案: