DropDownList绑定问题？

Question

var select1=from type in db.class
            group type by type.classid into id
            select id;

this.DropDownList1.DataSource=select1;
this.DropDownList1.DataTextField=?
this.DropDownList1.DataValueField=?
this.DropDownList1.DataBind();

我用classid 为int字段 ，group by以后 DataText 和DataValue应该怎么绑定;
我用了"classid"提示不包含此属性

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Lightning.T