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  • Entity Framework(05):主从表的增删改

    一、添加数据

    1、在主表中添加从表数据

    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();

    2、添加主表的同时添加从表数据

    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();

    3、添加从表的同时添加主表数据

    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();
    }

    二、修改关联

    1、修改从表的外键

    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();

    2、从表与主表脱离关系

    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();

    三、删除关联数据

    1、删除主表的同时删除相关联的从表数据(级联删除)

    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();

    2、普通删除

    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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  • 原文地址:https://www.cnblogs.com/springsnow/p/13230080.html
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