http://stackoverflow.com/questions/623672/update-entity-framework-objects
EF dbcontext update after find
http://www.google.com.hk/#hl=zh-CN&newwindow=1&safe=strict&site=&source=hp&q=entity+framework+dbcontext++entity+update&oq=entity+framework+dbcontext++entity+update&gs_l=hp.3...2219.26188.0.26406.42.30.1.4.5.0.344.1281.13j3-1.14.0...0.0..0.1c.8qKxZpKU16Y&bav=on.2,or.r_gc.r_pw.&fp=39a082fc1743e068&biw=1140&bih=581
http://social.msdn.microsoft.com/Forums/en-US/adonetefx/thread/e512431e-a620-4d33-b4dd-c6da96a05f79
http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx
http://blogs.msdn.com/b/adonet/archive/2011/01/30/using-dbcontext-in-ef-feature-ctp5-part-5-working-with-property-values.aspx