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我正在创建一个通用类来为数据库播种集成测试所需的实体。我可以创建单个实体，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班级首先创建父实体，然后继续。我试图使这种检测自动进行，从模型定义中获取具有多重性 0 或 1 的导航属性列表（参考导航属性），一旦完成，我的类将递归地调用自身以首先创建父实体（循环依赖项不在此范围内）。

我曾经在 EF for .net Framework 中执行此操作，但 EF Core 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对 Multiplicity 的任何引用，甚至艰难的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权并保留东西简单的。

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)
    });
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1 回答 1

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在查看 GitHub 中的源代码后，我可以有足够的信心说 EF Core 中不存在 Multiplicity 这样的东西。

我创建了一个枚举，就像使用的 .net Framework 3.5+ 一样（参见：官方文档）：

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：

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;
    }
}

使用示例：

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);
于 2019-03-03T12:15:53.010 回答