MyBatis中TypeHandler基本用法与示例

public interface TypeHandler<T> {
    // 设置 PreparedStatement 的参数
    void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;

    // 从 ResultSet 获取结果
    T getResult(ResultSet rs, String columnName) throws SQLException;

    T getResult(ResultSet rs, int columnIndex) throws SQLException;

    T getResult(CallableStatement cs, int columnIndex) throws SQLException;
}

public enum Status {
    ACTIVE("ACTIVE"),
    INACTIVE("INACTIVE");

    private final String value;

    Status(String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    public static Status fromString(String value) {
        for (Status status : Status.values()) {
            if (status.getValue().equalsIgnoreCase(value)) {
                return status;
            }
        }
        return null;
    }
}

@MappedTypes(Status.class)  // 指定适用于 Status 类型
public class StatusTypeHandler implements TypeHandler<Status> {

    @Override
    public void setParameter(PreparedStatement ps, int i, Status parameter, JdbcType jdbcType) throws SQLException {
        if (parameter != null) {
            ps.setString(i, parameter.getValue());  // 将枚举转换为数据库中的字符串
        } else {
            ps.setNull(i, Types.VARCHAR);
        }
    }

    @Override
    public Status getResult(ResultSet rs, String columnName) throws SQLException {
        String value = rs.getString(columnName);
        return Status.fromString(value);  // 将数据库中的字符串转换为枚举
    }

    @Override
    public Status getResult(ResultSet rs, int columnIndex) throws SQLException {
        String value = rs.getString(columnIndex);
        return Status.fromString(value);
    }

    @Override
    public Status getResult(CallableStatement cs, int columnIndex) throws SQLException {
        String value = cs.getString(columnIndex);
        return Status.fromString(value);
    }
}

<typeHandlers>
			 <typeHandler handler="org.mybatis.example.ExampleTypeHandler" 
										javaType="..." 
										jdbcType="..."/>
</typeHandlers>

public class User {
    private Integer id;
    private String username;
    private Status status;  // 使用自定义的枚举类型

    // Getters and Setters
}

public interface UserMapper {

    @Select("SELECT id, username, status FROM t_user WHERE id = #{id}")
    @Results({
        @Result(property = "status", column = "status", typeHandler = StatusTypeHandler.class)
    })
    User selectUserById(int id);

    @Insert("INSERT INTO t_user (username, status) VALUES (#{username}, #{status, typeHandler=com.example.handler.StatusTypeHandler})")
    void insertUser(User user);
}