Return list of Object inside Object with MyBatis

Question

I encountered problems when returning a list of Objects inside another Object when using MyBatis. My main object looks like this:

private Long id;

private String symbol;

private List<TypePermission> typePermissions;

and my mapper looks like this

<resultMap type="CalendarType" id="calendarTypeMap">
    <result column="id" property="id"/>
    <result column="symbol" property="symbol"/>
    <collection property="TypePermissions" resultMap="TypePermissions"/>
</resultMap>

<resultMap id="TypePermissions" type="TypePermission">
    <result property="roleId" column="roleId"/>
    <result property="permissionSymbol" column="permissionSymbol"/>
</resultMap>

My goal is to get an object like this:

content:[
    "id":id,
    "symbol":symbol,
    "TypePermissions":{
        "roleId":roleId,
        "permissionSymbol":permissionSymbol
    }
]

When I execute the sql query I get the following an error cannot find symbol TypePermissions, because the main SELECT tries to select rows such as TYPEPERMISSIONS, ID, SYMBOL

I searched over the internet, but failed to find anything useful. Could you help me and point out what am I doing wrong?

Answer 1

Please post your select snippet, I think this will ok:

<select id="selectCalendarType" parameterType="int" resultMap="calendarTypeMap">
    SELECT c.id,
    c.symbol
    t.roleId,
    t.permissionSymbol
    FROM CalendarType c
    LEFT JOIN TypePermission t ON c.id = t.c_id
    WHERE c.id = #{id}
</select>

And I think what you will get is actully something like this:

content:{
  "id":id,
  "symbol":symbol,
  "TypePermissions":[{
    "roleId":roleId,
    "permissionSymbol":permissionSymbol
  }]
}

And more about this you can read this example Nested_Results_for_Collection