I need to set collection for object in another collection using mybatis mappings.

It works for me w/o using columnPrefix, but I need it since there are a lot of repeteable columns.

    <collection property="childs"
        javaType="ArrayList" ofType="org.example.mybatis.Child"
        resultMap="ChildMap" columnPrefix="c_"/>       
</resultMap>

<resultMap id="ChildMap" type="org.example.mybatis.Parent">
    <id column="Id" jdbcType="VARCHAR" property="id" />
    <id column="ParentId" jdbcType="VARCHAR" property="parentId" />
    <id column="Name" jdbcType="VARCHAR" property="name" />
    <id column="SurName" jdbcType="VARCHAR" property="surName" />
    <id column="Age" jdbcType="INTEGER" property="age" />

    <collection property="toys"
        javaType="ArrayList" ofType="org.example.mybatis.Toy"
        resultMap="ToyMap" columnPrefix="t_"/>   
</resultMap>

<resultMap id="ToyMap" type="org.example.mybatis.Toy">
    <id column="Id" jdbcType="VARCHAR" property="id" />
    <id column="ChildId" jdbcType="VARCHAR" property="childId" />
    <id column="Name" jdbcType="VARCHAR" property="name" />
    <id column="Color" jdbcType="VARCHAR" property="color" />
</resultMap>

<sql id="Parent_Column_List">
    p.Id, p.Name, p.SurName,
</sql>  

<sql id="Child_Column_List">
    c.Id as c_Id, c.ParentId as c_ParentId, c.Name as c_Name, c.SurName as c_Surname, c.Age as c_Age,
</sql>

<sql id="Toy_Column_List">
    t.Id as t_Id, t.Name as t_Name, t.Color as t_Color
</sql>  

<select id="getParent" parameterType="java.lang.String" resultMap="ParentMap" >
    select 
    <include refid="Parent_Column_List"/>
    <include refid="Child_Column_List" />
    <include refid="Toy_Column_List" />
    from Parent p

    left outer join Child c on p.Id = c.ParentId
    left outer join Toy t on c.Id = t.ChildId
    where p.id = #{id,jdbcType=VARCHAR}

With columnPrefix all works fine, but nested toys collection is empty. Sql query on database works correctly and all toys are joined.

May be i missed something or this is bug with mybatis?