EF Core從多重性為零或一的模型中獲取實體的導航屬性

Question

我正在創建一個通用類，以使用集成測試所需的實體來為數據庫添加種子。 我可以創建單個實體，但是當一個實體彼此依賴時，我必須手動指示班級首先創建父實體，然后繼續。 我試圖使這種檢測自動進行，從模型定義中獲取多重性為0或1的導航屬性列表（參考導航屬性），一旦完成，遞歸地我的類將首先調用自身以創建父實體（循環依賴）在此超出范圍）。

我曾經在.net Framework EF中執行此操作，但EF Core發生了很大變化。 我在EF Core中缺少的是RelationshipMultiplicity ，我在官方文檔中找不到任何對Multiplicity的引用，甚至棘手的解決方案是檢查導航屬性是否為集合，我想擁有更多控制權並保留所有東西簡單。

到目前為止，我正在使用以下方法探索模型定義：

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

在檢查了GitHub中的源代碼之后，我可以很有把握地說，EF Core中沒有諸如Multiplicity之類的東西。

我創建了一個枚舉，類似於使用的.net Framework 3.5+（請參閱： 官方文檔 ）：

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

然后是擴展方法，該方法允許使用枚舉作為過濾器來獲取所有導航屬性。 我使用的關鍵是：

• 用於Inavigation的擴展方法稱為IsCollection
• ForeignKey.IsRequired屬性

該方法允許按關系類型獲取所有Navigations屬性

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);