Refrencing table data comes null

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data

model

entity-framework

I having three tables. first one is tbl_area and another is tbl_items.
the tbl_item have item record of area's.
The third table tbl_map maps both the table records, tbl_item and tbl_area.
There are also the foriegn key exist on the tbl_map.

I am using the framework 3.5
when I'm write the linq query for access the data from tbl_map.

example:
var id=**;
var data=context.tbl_map.FirstOrDefault(a=>a.pkmapId==id);

when I'm querying like this the refrencing table tbl_area and tbl_item data comes null.

Please give me your solutions.