如何在实体框架上实现左连接

本文关键字：实现 连接 框架 实体 | 更新日期: 2023-09-27 18:16:59

无论连接实体是否匹配，我都有一个从Contacts返回记录的问题。我正在尝试实现左连接的等效。

问题是，只有当联系人在所有相关表中包含一个关系时，查询才有效。我想返回联系人记录，而不考虑相关实体中的连接记录。

var SubQuery = from Contacts in db.Contacts
               join ContactAddictions in db.ContactAddictions.DefaultIfEmpty()
                    on Contacts.ID equals ContactAddictions.ContactID
               join ContactTreatmentPreferences in db.ContactTreatmentPreferences.DefaultIfEmpty()
                    on Contacts.ID equals ContactTreatmentPreferences.ContactID
               join TreatmentHistories in db.TreatmentHistories.DefaultIfEmpty()
                    on Contacts.ID equals TreatmentHistories.ContactID
               where
                    Contacts.ID == ID
               select Contacts;
var Query = SubQuery.Include("ContactAddictions")
    .Include("ContactTreatmentPreferences")
    .Include("ContactAddictions.Tag")
    .Include("ContactTreatmentPreferences.Tag")
    .Include("TreatmentHistories")
    .Include("TreatmentHistories.TreatmentCenter")
    .Include("ContactDispositionType")
    .Include("State");

如何在实体框架上实现左连接

感谢Serv的建议!

这是处理我的需求的最后一个查询。

      var SubQuery = from Contacts in db.Contacts
                       from ContactAddictions in db.ContactAddictions.DefaultIfEmpty()
                       from ContactTreatmentPreferences in db.ContactTreatmentPreferences.DefaultIfEmpty()
                       from TreatmentHistories in db.TreatmentHistories.DefaultIfEmpty()
                       orderby
                           Contacts.LastName, Contacts.FirstName
                       where
                            Contacts.ID == ID
                       select Contacts;
        var Query = SubQuery.Include("ContactAddictions")
            .Include("ContactTreatmentPreferences")
            .Include("ContactAddictions.Tag")
            .Include("ContactTreatmentPreferences.Tag")
            .Include("TreatmentHistories")
            .Include("TreatmentHistories.TreatmentCenter")
            .Include("ContactDispositionType")
            .Include("State");
        return Query.FirstOrDefault();
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