Normally when you select an identity for a class mapped to a view, the identity property should be mapped to a not-nullable column. This is because the identity should guarantee uniqueness of the objects, which is not possible without at least one not-nullable primary key column. This is a check we perform for each domain class, and if we detect that all columns mapped to the identity members are nullable, the aforementioned error is generated. This error does not prevent your project from building, but is there to warn you that there might be something wrong in the model.
If you are sure that your identity member is capable of providing uniqueness for all records, you can just ignore the error and continue working with your application, there should be no runtime problems because of that.
the Telerik team
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