多个自参考导航属性

Question

我们销售一种产品，我们为其颁发许可证编号，并且客户可以每年升级。我想设置一个License POCO，通过定义UpgradedTo 和UpgradedFrom 导航属性来跟踪此升级信息，这将使我们能够轻松地向上/向下移动相关许可证的“链”。所以基本上是这样的：

public class License
{
    [Key]
    public string LicenseNum { get; set; }
    // Other properties relating to license omitted...

    // Optional relationship.
    public License UpgradedTo { get; set; }

    // Optional relationship.
    public License UpgradedFrom { get; set; }
}

我真的很纠结如何使用 EF Annotations 和 Fluent API 来定义它。我认为自我参照方面是让我绊倒的地方。

我们还希望能够在给定 License 上设置这些 UpgradeTo/UpgradeFrom 属性之一，并让 EF 处理关系另一端的“相反”升级属性.所以类似于以下内容：

// Licenses upgraded 1 > 2 > 3
License lic1 = CreateLicense('1');
License lic2 = CreateLicense('2');
License lic3 = CreateLicense('3');

using (var db = new Model1())
{
    // Insert into database
    db.Licenses.Add(lic1);
    db.Licenses.Add(lic2);
    db.Licenses.Add(lic3);
    db.SaveChanges();

    // Specify UpgradeFrom/UpgradeTo info only on lic2.
    lic2.UpgradedFrom = lic1;
    lic2.UpgradedTo = lic3;
    db.SaveChanges();

    // lic1 and lic3 automatically update possible?
    Debug.Assert(lic1.UpgradedTo == lic2);
    Debug.Assert(lic3.UpgradedFrom == lic2);
}

Answer 1

这种情况非常棘手，因为依赖是如何工作的。

诀窍是添加一个或多个额外的“假”属性来完成这项工作。

如果您设置 UpgradeTo 值，此类将自动设置 UpgradedFrom 属性。

示例：

using (var ctx = new TestContext2())
{
    var license1 = ctx.Licenses.Add(new License() { LicenseNum = "1.0.0"});
    ctx.SaveChanges();

    var license2 = license1.UpgradeTo = new License() { LicenseNum = "1.0.2"};
    ctx.SaveChanges();

    var license3 = license2.UpgradeTo = new License() { LicenseNum = "1.0.3" };
    ctx.SaveChanges();
}

实体

public class License
{
    [Key]
    public string LicenseNum { get; set; }

    private License _upgradeTo;
    private License _upgradedFrom;


    public License UpgradeTo
    {
        get { return _upgradeTo; }
        set
        {
            _upgradeTo = value;
            if (_upgradeTo != null && _upgradeTo.UpgradedFrom != this)
            {
                _upgradeTo.UpgradedFrom = this;
            }
        }
    }

    public License UpgradedFrom
    {
        get { return _upgradedFrom; }
        set
        {
            _upgradedFrom = value;
            if (_upgradedFrom != null && _upgradedFrom.UpgradeTo != this)
            {
                _upgradedFrom.UpgradeTo = this;
            }
        }
    }

    internal License InternalUpgradedTo
    {
        get { return UpgradeTo; }
    }

    internal License InternalUpgradedFrom
    {
        get { return UpgradedFrom; }
    }
}

上下文

public  class TestContext2 : DbContext
{
    public TestContext2() : base(My.Config.ConnectionStrings.TestDatabase)
    {

    }
    public DbSet<License> Licenses { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<License>()
            .HasOptional(v => v.UpgradeTo)
            .WithOptionalDependent(x => x.InternalUpgradedFrom);

        modelBuilder.Entity<License>()
            .HasOptional(v => v.UpgradedFrom)
            .WithOptionalDependent(x => x.InternalUpgradedTo);
    }
}