保证EF上下文实例是线程内唯一

public class DbContextFactory    {       /// <summary>       /// 保证EF上下文实例是线程内唯一。       /// </summary>       /// <returns></returns>       public static DbContext CreateDbContext()       {           DbContext dbContext = (DbContext)CallContext.GetData("dbContext");           if (dbContext == null)           {               dbContext = new OAEntities();               CallContext.SetData("dbContext", dbContext);           }           return dbContext;       }    }public class DbContextFactory    {       ///