Note the EDM of ADO. NET Entity Framework

1. All Tables must have a primary key. Otherwise, the table entity cannot be generated.

2. All views must have a not null field out. Otherwise, the table entity cannot be generated.

Or manually modify the EDM file and add <entitytype name = "department"
<Key>
<Propertyref name = "departmentid">
</Key>
<Property name = "inclumentid" type = "int16" nullable = "false"/>
See: http://msdn.microsoft.com/en-us/library/bb399288.aspx

If you want to re-add EDM, you must first Delete the existing connection in APP. config. Otherwise, it will be unable to be added because of duplicate names. modelnamespace can be input randomly and is useless.