EF Core从模型中获取具有多重性零或一的实体的导航属性

Question

我正在创建一个通用类，用于为集成测试所需的实体播种数据库。我可以创建单个实体，但当一个实体依赖另一个实体时，我必须手动指示我的类首先创建父实体然后继续。我试图自动进行这种检测，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，递归我的类将调用自己首先创建父实体（循环依赖性）超出范围）。

我曾经在EF for .net Framework中这样做，但EF Core已经发生了很大的变化。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，甚至强硬的hacky解决方案是检查导航属性是否是一个集合，我希望有更多的控制和保持事物简单。

到目前为止，我正在探索模型定义：

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中的源代码之后，我可以充分相信在EF Core中没有Multiplicity这样的东西。

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
}

然后是一个扩展方法，它允许使用枚举作为过滤器获取所有导航属性。我使用的关键是：

• INavigation的扩展方法称为IsCollection
• ForeignKey.IsRequired财产

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);