EF Core 从具有多重性零或一的模型中获取实体的导航属性

Question

我正在创建一个通用的 class 来为数据库植入集成测试所需的实体。我可以创建单独的实体，但是当一个实体依赖于另一个实体时，我必须手动指示我的 class 先创建父实体，然后再继续。我正在尝试自动进行此检测，从模型定义中获取多重性为 0 或 1 的导航属性列表（参考导航属性），一旦完成，我的 class 将递归地调用自身来创建父实体首先（循环依赖超出了这里的范围）。

我以前在 EF for .net Framework 中这样做，但 EF Core 已经发生了很大变化。我在 EF Core 中缺少的是 RelationshipMultiplicity，我在官方文档中找不到任何对 Multiplicity 的引用，甚至艰难的 hacky 解决方案是检查导航属性是一个集合，我想有更多的控制权，让事情变得简单。

到目前为止，我正在使用以下方法探索模型定义：

var modelData = _context.Model.GetEntityTypes()
    .Select(t => new
    {
        t.ClrType.Name,
        DerivedNavigationProperties = t.FindDerivedNavigations(t.ClrType.Name),
        DefiningNavigationProperties = t.FindDefiningNavigation(),
        DeclaredForeignKeys = t.GetDeclaredForeignKeys(),
        DeclaredNavigations = t.GetDeclaredNavigations(),
        DerivedNavigations = t.GetDerivedNavigations(),
        DerivedNavigationsInclusive = t.GetDerivedNavigationsInclusive(),
        Navigations = t.GetNavigations() // This returns all Navigation Properties (INavigation)
    });

Answer 1

在检查 GitHub 中的源代码后，我可以自信地说，EF Core 中没有多重性。

我创建了一个类似于 .net Framework 3.5+ 的枚举（参见：Official documentation）：

public enum RelationshipMultiplicity
{
    Many = 2,
    One = 1,
    ZeroOrOne = 0
}

然后是允许使用枚举作为过滤器获取所有导航属性的扩展方法。我使用的关键是：

名为 INavigation 的扩展方法 IsCollection
ForeignKey.IsRequired 属性

该方法允许按关系类型获取所有导航属性

public static class ModelExtensions
{
    /// <summary>
    /// Extension method used to get from the entity all navigation properties by multiplicity
    /// </summary>
    /// <typeparam name="T">Entity from where the navigation properties are taken</typeparam>
    /// <param name="model">Context Model</param>
    /// <param name="multiplicity">Type of multiplicity to use</param>
    /// <returns>List of PropertyInfo of Navigation Properties</returns>
    public static IEnumerable<PropertyInfo> GetNavigationProperties<T>(this IModel model, RelationshipMultiplicity multiplicity)
    {
        var navigations = model.GetEntityTypes().FirstOrDefault(m => m.ClrType == typeof(T))?.GetNavigations();
        var properties = new List<PropertyInfo>();

        switch (multiplicity)
        {
            case RelationshipMultiplicity.Many | RelationshipMultiplicity.ZeroOrOne:
                return navigations?
                    .Select(nav => nav.PropertyInfo);
            case RelationshipMultiplicity.Many:
                return navigations?
                    .Where(nav => nav.IsCollection())
                    .Select(nav => nav.PropertyInfo);
            case RelationshipMultiplicity.One:
                return navigations?
                    .Where(nav => !nav.IsCollection() && nav.ForeignKey.IsRequired)
                    .Select(nav => nav.PropertyInfo);
            case RelationshipMultiplicity.ZeroOrOne:
                return navigations?
                    .Where(nav => !nav.IsCollection())
                    .Select(nav => nav.PropertyInfo);
            default:
                return null;
        }

        return properties;
    }
}

用法示例：

var oneToManyRelations = _context.Model.GetNavigationProperties<Transaction>(
    RelationshipMultiplicity.ZeroOrOne);

var manyToOneRelations = _context.Model.GetNavigationProperties<Transaction>(
    RelationshipMultiplicity.Many);

var allRelations = _context.Model.GetNavigationProperties<Transaction>(
    RelationshipMultiplicity.Many | 
    RelationshipMultiplicity.ZeroOrOne);

EF Core 从具有多重性零或一的模型中获取实体的导航属性

EF Core get Navigation Properties of an entity from Model with multiplicity Zero or One

c#

navigation-properties

ef-core-2.2