MyBatis-Plus implements elegant handling of JSON field mapping

When using MyBatis-Plus for business development, we often need to automatically map the JSON fields in the database (such as arrays in strings) into JSONArray or List<String> types in Java.

By default, MyBatis-Plus does not support direct mapping of JSON types, so you need to use:

• @TableField(typeHandler = ...)
• Custom or existing TypeHandler
• Only when it works correctly can it work with @TableName(autoResultMap = true)!

Examples of real scenes

Suppose we now have a travel food table travel_cuisine, and the field tag_list inside is a JSON Array, which is used to store the tag ID list, and the sample data is as follows:

["tag-101", "tag-202", "tag-333"]

We want to use the following form to automatically map in Java entities:

@TableField(typeHandler = )
private JSONArray tagList;

Next, I will teach you to implement it step by step.

1. What is @TableField + typeHandler?

@TableField Introduction

@TableField is a field-level annotation provided by MyBatis-Plus, which is used to illustrate the mapping relationship between fields and databases.

The core parameters are as follows:

typeHandler function

TypeHandler is an important mechanism in MyBatis, which is responsible for the conversion between Java types and JDBC types.

You can use it to handle:

• JSON ↔ Java objects (such as JSONArray, Map, List)
• Comma-separated string ↔ List
• Enumeration ↔ Database storage values

Simply put, typeHandler is the bridge of data format!

2. @TableName(autoResultMap = true) must be enabled

By default, MyBatis-Plus field mapping does not use typeHandler unless you add:

@TableName(value = "travel_cuisine", autoResultMap = true)

What is autoResultMap?

This is telling MP: "Please generate a custom ResultMap, otherwise I don't support typeHandler and complex types conversions!"

If you forget to add this item, typeHandler will not take effect!

3. Practical code: Map the JSON field as JSONArray

1. Database table building statement (simplified version)

CREATE TABLE travel_cuisine (
  id BIGINT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(100),
  tag_list TEXT -- JSON Array String
);

2. Entity class configuration

@Data
@TableName(value = "travel_cuisine", autoResultMap = true)
public class TravelCuisineDO {

    private Long id;

    private String name;

    @TableField(typeHandler = )
    private JSONArray tagList;
}

3. Custom TypeHandler (based on FastJSON)

public class JsonArrayTypeHandler extends BaseTypeHandler<JSONArray> {

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, JSONArray parameter, JdbcType jdbcType) throws SQLException {
        (i, ());
    }

    @Override
    public JSONArray getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String result = (columnName);
        return (result);
    }

    @Override
    public JSONArray getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String result = (columnIndex);
        return (result);
    }

    @Override
    public JSONArray getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String result = (columnIndex);
        return (result);
    }
}

Reminder: This JsonArrayTypeHandler uses FastJSON. If Jackson is needed, please replace the conversion logic.

4. FAQ Troubleshooting Guide

Summary: Three things must be used together

This is the article about MyBatis-Plus implementing elegant processing of JSON field mapping. For more related content related to MyBatis-Plus processing of JSON field mapping, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!