Entity framework query returns the same row multiple times

This is my first time using the Entity Framework and I'm getting some confusing results. I know a particular table contains 3 distinct rows when I run this SQL query:

SELECT * FROM mytable WHERE service_month = 201012

When I run this query against the framework however, I get 3 rows, but they are all copies of the first row (VB syntax).

Dim temp 开发者_StackOverflow中文版= _context.mytable.Where(Function(x) x.service_month = 201012)

Did I set up something incorrectly? This is how I'd do it with LINQ to SQL so I feel like I'm missing something.

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Fix your primary key definition in your EDMX. (If your table has no PK, add one.) When all rows return the same "key", the EF returns the same object instance.

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I experienced this in Code First 5.0.13 when I had used a [Key] attribute in the business object that came from the wrong library. It should be

System.ComponentModel.DataAnnotations.KeyAttribute