Use guid with caution in Entity Framework?

I recently encountered a series of strange problems when using EF and data service, probably because I used guid as the foreign key of the primary key.

For example:

VaR C2 = Dc. categories. Where (O => O. categoryid = C. categoryid). First ();

Categoryid is of the long type and can run normally.

And:

VaR customers = Dc. Customers. Where (O => O. customerid = new GUID ("4c65d18f-9ff1-4c31-accd-1fea164ef507 "));

If customerid is of the guid type, no data is found.

Must be changed:

Guid gid = new GUID ("4c65d18f-9ff1-4c31-accd-1fea164ef507 ");
VaR customers = Dc. Customers. Where (O => O. customerid = GID );

The following are some references:

Http://msdn.microsoft.com/en-us/library/dd283139.aspx

Http://geekswithblogs.net/SudheersBlog/archive/2009/06/11/132758.aspx

In addition, when GUID is used as the foreign key type, you cannot add the data in the detail table correctly. The following table structure:

Product

Productid	Guid
Categoryid	Guid
Productname	String

Category

Categoryid	Guid
Categoryname	String

Write the following code:CodeCannot run correctly:

Dataservicecontext Dc = new dataservicecontext ();

Category C = combobox1.selecteditem as category;

Product P = new product ()

{

Category = C,

Productname = "some good"

}

DC. addtoproduct (P );

DC. setlink (p, "category", p. Category );

DC. savechanges ();

If you change the data type of the preceding ID to string or number, the above Code runs correctly.