linq - ハードコードされた文字列の代わりにEF4LINQInclude（string）？

Question

これに代わるものはありますか？

Organizations.Include("Assets").Where(o => o.Id == id).Single()

私は次のようなものを見たいです：

Organizations.Include(o => o.Assets).Where(o => o.Id == id).Single()

ハードコードされた文字列「Assets」を回避するため。

Answer 1

Entity Framework 1.0 では、これを行うためのいくつかの拡張メソッドを作成しました。

public static class EntityFrameworkIncludeExtension
{
    public static ObjectQuery<T> Include<T>(this ObjectQuery<T> src, Expression<Func<T, StructuralObject>> fetch)
    {
        return src.Include(CreateFetchingStrategyDescription(fetch));
    }

    public static ObjectQuery<T> Include<T>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch)
    {
        return src.Include(CreateFetchingStrategyDescription(fetch));
    }

    public static ObjectQuery<T> Include<T, TFectchedCollection>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<TFectchedCollection>>> fetch)
    {
        return src.Include(CreateFetchingStrategyDescription(fetch));
    }

    public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch, Expression<Func<FetchedChild, Object>> secondFetch)
        where FetchedChild : StructuralObject
    {
        return src.Include(CombineFetchingStrategies(fetch, secondFetch));
    }

    public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch, Expression<Func<FetchedChild, RelatedEnd>> secondFetch)
        where FetchedChild : StructuralObject
    {
        return src.Include(CombineFetchingStrategies(fetch, secondFetch));
    }

    public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch, Expression<Func<FetchedChild, StructuralObject>> secondFetch)
        where FetchedChild : StructuralObject
    {
        return src.Include(CombineFetchingStrategies(fetch, secondFetch));
    }

    public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<FetchedChild>>> fetch, Expression<Func<FetchedChild, Object>> secondFetch)
        where FetchedChild : StructuralObject
    {
        return src.Include(CombineFetchingStrategies(fetch, secondFetch));
    }

    public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<FetchedChild>>> fetch, Expression<Func<FetchedChild, RelatedEnd>> secondFetch)
        where FetchedChild : StructuralObject
    {
        return src.Include(CombineFetchingStrategies(fetch, secondFetch));
    }

    public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<FetchedChild>>> fetch, Expression<Func<FetchedChild, StructuralObject>> secondFetch)
        where FetchedChild : StructuralObject
    {
        return src.Include(CombineFetchingStrategies(fetch, secondFetch));
    }

    private static String CreateFetchingStrategyDescription<TFetchEntity, TFetchResult>(
        Expression<Func<TFetchEntity, TFetchResult>> fetch)
    {
        fetch = (Expression<Func<TFetchEntity, TFetchResult>>)FixedWrappedMemberAcces.ForExpression(fetch);
        if (fetch.Parameters.Count > 1)
            throw new ArgumentException("CreateFetchingStrategyDescription support only " +
                "one parameter in a dynamic expression!");

        int dot = fetch.Body.ToString().IndexOf(".") + 1;
        return fetch.Body.ToString().Remove(0, dot);
    }

    private static String CreateFetchingStrategyDescription<T>(Expression<Func<T, Object>> fetch)
    {
        return CreateFetchingStrategyDescription<T, Object>(fetch);
    }

    private static String CombineFetchingStrategies<T, TFetchedEntity>(
                Expression<Func<T, Object>> fetch, Expression<Func<TFetchedEntity, Object>> secondFetch)
    {
        return CombineFetchingStrategies<T, Object, TFetchedEntity, Object>(fetch, secondFetch);
    }

    private static String CombineFetchingStrategies<TFetchEntity, TFetchResult, TFetchedEntity, TSecondFetchResult>(
        Expression<Func<TFetchEntity, TFetchResult>> fetch, Expression<Func<TFetchedEntity, TSecondFetchResult>> secondFetch)
    {
        return CreateFetchingStrategyDescription<TFetchEntity, TFetchResult>(fetch) + "." +
            CreateFetchingStrategyDescription<TFetchedEntity, TSecondFetchResult>(secondFetch);
    }
}

使用法：

 Orders.Include(o => o.Product); // generates .Include("Product")
 Orders.Include(o => o.Product.Category); // generates .Include("Product.Category")
 Orders.Include(o => o.History); // a 1-* reference => .Include("History")
 // fetch all the orders, and in the orders collection.
 // also include the user reference so: .Include("History.User")
 // but because history is an collection you cant write o => o.History.User, 
 // there is an overload which accepts a second parameter to describe the fetching 
 // inside the collection.
 Orders.Include(o => o.History, h => h.User); 

EF4.0 でこれをテストしていませんが、動作することを期待しています。

Answer 2

Expressions を使用すると、非常に簡単に実行できます。

public static class ObjectQueryExtensions
{
    public static ObjectQuery<T> Include<T, TProperty>(this ObjectQuery<T> objectQuery, Expression<Func<T, TProperty>> selector)
    {
        MemberExpression memberExpr = selector.Body as MemberExpression;
        if (memberExpr != null)
        {
            return objectQuery.Include(memberExpr.Member.Name);
        }
        throw new ArgumentException("The expression must be a MemberExpression", "selector");
    }
}

質問の例とまったく同じように使用できます

---

アップデート

複数の連鎖プロパティをサポートする改良版:

public static class ObjectQueryExtensions
{
    public static ObjectQuery<T> Include<T, TProperty>(this ObjectQuery<T> objectQuery, Expression<Func<T, TProperty>> selector)
    {
        string propertyPath = GetPropertyPath(selector);
        return objectQuery.Include(propertyPath);
    }

    public static string GetPropertyPath<T, TProperty>(Expression<Func<T, TProperty>> selector)
    {
        StringBuilder sb = new StringBuilder();
        MemberExpression memberExpr = selector.Body as MemberExpression;
        while (memberExpr != null)
        {
            string name = memberExpr.Member.Name;
            if (sb.Length > 0)
                name = name + ".";
            sb.Insert(0, name);
            if (memberExpr.Expression is ParameterExpression)
                return sb.ToString();
            memberExpr = memberExpr.Expression as MemberExpression;
        }
        throw new ArgumentException("The expression must be a MemberExpression", "selector");
    }
}

例 ：

var query = X.Include(x => x.Foo.Bar.Baz) // equivalent to X.Include("Foo.Bar.Baz")

Answer 3

「ハードコーディングされた ObjectQuery(T).Include 呼び出しに別れを告げる」を参照してください。

Answer 4

別の解決策は、EntitySet.Name を使用してエンティティ名を取得することです。
コードは次のようになります。

var context = new DBContext();  
context.Organizations.Include(context.Assets.EntitySet.Name).Where(o => o.Id == id).Single()

Answer 5

もう 1 つのオプションは、TT テンプレートを使用してクラス内に内部部分クラスを含めることです。

T4 コード:

<#
    region.Begin("Member Constants");
#>
   public partial class <#=code.Escape(entity)#>Members
   {
<#
    foreach (EdmProperty edmProperty in entity.Properties.Where(p => p.TypeUsage.EdmType is PrimitiveType && p.DeclaringType == entity))
    {
        bool isForeignKey = entity.NavigationProperties.Any(np=>np.GetDependentProperties().Contains(edmProperty));
        bool isDefaultValueDefinedInModel = (edmProperty.DefaultValue != null);
        bool generateAutomaticProperty = false;
        #>
        public const string <#=code.Escape(edmProperty)#> = "<#=code.Escape(edmProperty)#>";
        <#
    }
    #>
    }
    <#
    region.End();
#>

次のようなものが生成されます。

    #region Member Constants
   public partial class ContactMembers
   {
        public const string ID = "ID";
                public const string OriginalSourceID = "OriginalSourceID";
                public const string EnabledInd = "EnabledInd";
                public const string EffectiveDTM = "EffectiveDTM";
                public const string EndDTM = "EndDTM";
                public const string EnterDTM = "EnterDTM";
                public const string EnterUserID = "EnterUserID";
                public const string LastChgDTM = "LastChgDTM";
                public const string LastChgUserID = "LastChgUserID";
            }

    #endregion

Answer 6

EF4 CTP4 が現在この機能をサポートしていることは朗報です。