DataContext-通过LINQ查询时自动加载可选引用值

我有以下情况（例如）

我有一个名为Master.dbml的DataContext

它有两个表：

• 爱好{id；name；}
• HobbyReference{id；Hobby\u Name；Hobby\u Good\u Name；}

当我查询Hobby时，DataContext应该检查（伪代码）：

这方面的最佳实践是什么

我知道如何做（扩展datacontext），但不知道如何完全实现它

---

我该怎么做？

业余爱好。业余爱好的名称不存在

无论如何，要在从datacontext返回之前进行检查，您可以执行以下操作：

public class HobbyDataService
    {
        MasterDataContext db = null;

        public HobbyDataService(string connection)
        {
            db = new MasterDataContext(connection);
        }

        internal string GetHoppyName(string hobbyName)
        {
            var x = from hr in this.db.HobbyReferences
                    where string.Equals(hr.Hoppy_Name, hobbyName)
                    select hr;
            if (x.Any())
                return x.First().Hobby_Good_Name;
            else
            {
                //Return what ever you want here
            }
        }
    }

 public partial class Hobby
    {
        public static string GetName(string hobbyName, string connection)
        {
            if (String.IsNullOrEmpty(hobbyName))
                throw new ArgumentException("hobbyName is null or empty.", "hobbyName");
            if (String.IsNullOrEmpty(connection))
                throw new ArgumentException("connection is null or empty.", "connection");

            HobbyDataService dataSrvce = new HobbyDataService(connection);
            return dataSrvce.GetHoppyName(hobbyName);
        }
    }

如果每个名字在HobbyReference上的条目不超过一个，并且用于查询（即不用于更新），那么您可以执行以下操作

public class AmendedHobby
{
    public int Id  { get; set ;} 
    public string Name{ get; set ;} 
}

public IQueryable<AmendedHobby>  GetAmendedHobbies()
{
    return 
     (from h in Hobby
      join hr in HobbyRefernce on h.Name equals hr.Name into hrResults
      from hr in hrResults.DefaultIfEmpty()
      select new { h.id , Name = hr.Hobby_Good.Name ?? r.Name}  
}

它将返回AmendDedHobby类，因为它没有链接到现有表，这意味着更改不会持久化回数据库

public class AmendedHobby
{
    public int Id  { get; set ;} 
    public string Name{ get; set ;} 
}

public IQueryable<AmendedHobby>  GetAmendedHobbies()
{
    return 
     (from h in Hobby
      join hr in HobbyRefernce on h.Name equals hr.Name into hrResults
      from hr in hrResults.DefaultIfEmpty()
      select new { h.id , Name = hr.Hobby_Good.Name ?? r.Name}  
}

 (from r in GetAmendedHobbies() where r.Name == "Football" select r)