本篇内容介绍了“Entity Framework主从表的增删改怎么实现”的有关知识,在实际案例的操作过程中,不少人都会遇到这样的困境,接下来就让小编带领大家学习一下如何处理这些情况吧!希望大家仔细阅读,能够学有所成!
在景点的住宿集合(Lodgings)中增加一个度假区(Resort)
var dest = (from d in context.Destinations where d.Name == "Bali" select d).Single(); var resort = new CodeFirst.Model.Resort { Name = "Pete's Luxury Resort", }; dest.Lodgings.Add(resort); context.SaveChanges();
添加一个带两个住宿的景点
var destination = new CodeFirst.Model.Destination { Name = "AnHui HuangShan", Lodgings = new List { new CodeFirst.Model.Lodging {Name="HuangShan Hotel"}, new CodeFirst.Model.Lodging {Name="YingKeSong Hotel"} } }; context.Destinations.Add(destination); context.SaveChanges();
添加一个带有景点信息度假村到住宿信息中。
var resort = new CodeFirst.Model.Resort { Name = "Top Notch Resort and Spa", Destination = new CodeFirst.Model.Destination { Name = "Stowe, Vermont", Country = "USA" } }; using (var context = new CodeFirst.DataAccess.BreakAwayContext()) { context.Lodgings.Add(resort); context.SaveChanges(); }
var hotel = (from l in context.Lodgings where l.Name == "YingKeSong Hotel" select l).Single(); var reef = (from d in context.Destinations where d.Name == "Bali" select d).Single(); hotel.Destination = reef; context.SaveChanges();
1、ForeignKeys方式:
var davesDump = (from l in context.Lodgings where l.Name == "HuangShan Hotel" select l).Single(); davesDump.DestinationID = null;//(ForeignKeys方式) context.SaveChanges();
2、Reference方式:
var davesDump = (from l in context.Lodgings where l.Name == "HuangShan Hotel" select l).Single(); context.Entry(davesDump).Reference(l => l.Destination).Load(); //找主表数据 davesDump.Destination = null; //清空,(Reference方式) context.SaveChanges();
如果数据库里设置是级联删除,则不显示加载从表数据。
var canyon = (from d in context.Destinations where d.Name == "AnHui HuangShan" select d).Single(); context.Entry(canyon).Collection(d => d.Lodgings).Load(); //从表显示加载后,再删除主表数据 context.Destinations.Remove(canyon); context.SaveChanges();
删除主表数据,同时标注从表数据为删除状态(数据库关闭了级联删除的情况,可以手动去数据库的外键关系修改,也可以Fluent API配置关闭级联删除)
var canyon = (from d in context.Destinations where d.Name == "Grand Canyon" select d).Single(); foreach (var lodging in canyon.Lodgings.ToList()) { context.Lodgings.Remove(lodging); //先标记相关的从表数据为删除状态 } context.Destinations.Remove(canyon); //再标记主表数据为删除装填 context.SaveChanges(); //执行上面的所有标记
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