{"id":5216,"date":"2021-08-03T12:57:05","date_gmt":"2021-08-03T11:57:05","guid":{"rendered":"https:\/\/solidt.eu\/site\/?page_id=5216"},"modified":"2025-04-17T16:28:31","modified_gmt":"2025-04-17T15:28:31","slug":"linq-helper","status":"publish","type":"post","link":"https:\/\/solidt.eu\/site\/linq-helper\/","title":{"rendered":"C# LinqHelper"},"content":{"rendered":"\n
public static class LinqHelper\n{\n    public static IEnumerable<T> Select<T>(params T[] args) => args;\n    \n    public static IEnumerable<T> SelectMany<T>(params IEnumerable<T>[] args) => args.SelectMany(x => x);\n\n    public static List<T> List<T>(params T[] args) => args.ToList();\n    \n    public static IEnumerable<T> Init<T>(int count, Func<int, T> init) => Enumerable.Range(0, count).Select(i => init(i));\n    \n    public static IEnumerable<IEnumerable<T>> Split<T>(IEnumerable<T> src, int size) => src.Where((x, i) => i % size == 0).Select((x, i) => src.Skip(i * size).Take(size));\n    \n    public static bool HasSharedItem<T>(IEnumerable<T> left, IEnumerable<T> right) => left.Any(l => right.Any(r => l != null && r != null && l.Equals(r)));\n\n    public static T GetValueIfExactOne<T>(IEnumerable<T> values, T defValue = default)\n    {\n        var distinct = values.Distinct();\n        return distinct.Count() == 1 ? distinct.First() : defValue;\n    }\n\n    public static async Task<IEnumerable<T>> FromAsync<T>(IAsyncEnumerable<T> items)\n    {\n        var list = new List<T>();\n        await foreach (var item in items) { list.Add(item); }\n        return list;\n    }\n    \n    public static async Task<IEnumerable<U>> FromAsync<T, U>(IAsyncEnumerable<T> items, Func<T, U> converter)\n    {\n        var list = new List<U>();\n        await foreach (var item in items) { list.Add(converter(item)); }\n        return list;\n    }\n    \n    public static T MinOrDefault<T>(this IEnumerable<T> sequence, T defValue = default(T)) => sequence.Any() ? sequence.Min() : defValue;\n    public static T MaxOrDefault<T>(this IEnumerable<T> sequence, T defValue = default(T)) => sequence.Any() ? sequence.Max() : defValue;\n    \n    public static IEnumerable<(T item, int index)> WithIndex<T>(this IEnumerable<T> self) => self.Select((item, index) => (item, index));\n\n    \/\/ filter where conditions in (Entity Framework) queries based on condition e.g:\n    \/\/ AsQueryable().WhereIf(onlyActiveItems, x => x.Active).ToListAsync();\n    public static IEnumerable<TSource> WhereIf<TSource>(this IEnumerable<TSource> source, bool condition, Func<TSource, bool> predicate) where TSource : class\n    {\n        return condition ? source.Where(predicate) : source;\n    }\n\n    public static IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Expression<Func<TSource, bool>> predicate) where TSource : class\n    {\n        return condition ? source.Where(predicate) : source;\n    }\n\n    public static IQueryable<TSource> IncludeIf<TSource, TProperty>(this IQueryable<TSource> source, bool condition, Expression<Func<TSource, TProperty>> propertySelector) where TSource : class\n    {\n        return condition ? source.Include(propertySelector) : source;\n    }\n\n    public static IQueryable<TSource> SkipIf<TSource>(this IQueryable<TSource> source, bool condition, int quantityToSkip) where TSource : class\n    {\n        return condition ? source.Skip(quantityToSkip) : source;\n    }\n    \n    public static IEnumerable<T> SelectRecursive<T>(this IEnumerable<T> source, Func<T, IEnumerable<T>> recursiveSelector)\n    {\n        foreach (var i in source)\n        {\n            yield return i;\n\n            var directChildren = recursiveSelector(i);\n            var allChildren = SelectRecursive(directChildren, recursiveSelector);\n\n            foreach (var c in allChildren)\n            {\n                yield return c;\n            }\n        }\n    }\n\n    public static IQueryable<TSource> TakeIf<TSource>(this IQueryable<TSource> source, bool condition, int quantityToTake) where TSource : class\n    {\n        return condition ? source.Take(quantityToTake) : source;\n    }\n    \n    public static Dictionary<Y, T> ToDictionarySafe<T, Y>(this IEnumerable<T> items, Func<T, Y> keySelector) => items.GroupBy(x => keySelector(x)).Where(x => x.Key != null).Select(x => x.First()).ToDictionary(x => keySelector(x));\n    \n\t\/\/ Comparable with: .GroupBy(x => x.Property).Select(x => x.First())\n\t\/\/ but possibly faster and with yield return\n\t\/\/ update: function exists in dotnet 6\n\tpublic static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)\n\t{\n\t\tvar seenKeys = new HashSet<TKey>();\n\t\tforeach (TSource element in source)\n\t\t\tif (seenKeys.Add(keySelector(element)))\n\t\t\t\tyield return element;\n\t}\n\t\n    public static bool ContainsDuplicates<T>(this IEnumerable<T> enumerable)\n    {\n        var knownKeys = new HashSet<T>();\n        return enumerable.Any(item => !knownKeys.Add(item));\n    }\n\n    public static bool None<T>(this IEnumerable<T> list) => !list.Any();\n        \n\tpublic static IEnumerable<int> GetRange(int min, int max)\n\t{\n\t\tfor (var i = min; i <= max; i++)\n\t\t\tyield return i;\n\t}\n\n\tpublic static List<List<T>> Transpose<T>(this IEnumerable<IEnumerable<T>> list)\n\t{\n\t\treturn list\n\t\t\t.SelectMany(inner => inner.Select((item, index) => new { item, index }))\n\t\t\t.GroupBy(i => i.index, i => i.item)\n\t\t\t.Select(g => g.ToList())\n\t\t\t.ToList();\n\t}\n\t\n\tpublic static (List<T> TrueItems, List<T> FalseItems) Partition<T>(this IEnumerable<T> source, Func<T, bool> predicate)\n    {\n        var trueItems = new List<T>();\n        var falseItems = new List<T>();\n        foreach (var item in source)\n        {\n            if (predicate(item))\n                trueItems.Add(item);\n            else\n                falseItems.Add(item);\n        }\n        return (trueItems, falseItems);\n    }\n\n    \/\/ Cartesian product of two sets A and B, denoted A \u00d7 B, is the set of all ordered pairs\n    public static IEnumerable<IEnumerable<T>> Cartesian<T>(IEnumerable<IEnumerable<T>> sequences)\n    {\n        return sequences.Aggregate(Enumerable.Repeat(Enumerable.Empty<T>(), 1), (accumulator, sequence) => accumulator.SelectMany(acc => sequence.Select(item => acc.Append(item))));\n    }\n    \n    public static TimeSpan SumTimespan<TSource>(this IEnumerable<TSource> source, Func<TSource, TimeSpan> predicate) => source.Select(predicate).Aggregate(TimeSpan.Zero, (a, c) => a + c);\n}<\/pre><\/div>\n\n\n\n
WhereIf example<\/p>\n\n\n\n
\/\/ Original: query with separate if statements\npublic async Task<IEnumerable<PurchaseContractExpectedAndDelivered>> GetExpectedAndDeliveredQuantitiesForContract(PurchaseQuantityFilter filter)\n{\n\tusing var unitOfWork = GetUnitOfWork();\n\n\tvar query = Query<DmPurchaseContractLine>(unitOfWork);\n\t\n\tif (filter.PurchaseContractId != null)\n\t\tquery = query.Where(x => x.PurchaseContractId == filter.PurchaseContractId)\n\t\t\n\tif (filter.PurchaseContractLineId != null)\n\t\tquery = query.Where(x => x.Id == filter.PurchaseContractLineId);\n\n\tvar selectQuery = query.Select(x => new PurchaseContractExpectedAndDelivered\n\t{\n\t\tPurchaseContractId = x.PurchaseContractId,\n\t\tPurchaseContractLineId = x.Id,\n\t\tExpectedKg = x.WeightKg,\n\t\tDeliveredKg = x.PurchaseShipments.Sum(x => x.WeightKg),\n\t\tDeliveredBoxes = x.PurchaseShipments.Sum(x => x.Boxes),\n\t});\n\n\treturn await selectQuery.ToListAsync();\n}\n\n\/\/ With an WhereIf: query as single statement\npublic async Task<IEnumerable<PurchaseContractExpectedAndDelivered>> GetExpectedAndDeliveredQuantitiesForContract(PurchaseQuantityFilter filter)\n{\n\tusing var unitOfWork = GetUnitOfWork();\n\n\tvar query = Query<DmPurchaseContractLine>(unitOfWork)\n\t\t.WhereIf(filter.PurchaseContractId != null, x => x.PurchaseContractId == filter.PurchaseContractId)\n\t\t.WhereIf(filter.PurchaseContractLineId != null, x => x.Id == filter.PurchaseContractLineId);\n        .Select(x => new PurchaseContractExpectedAndDelivered\n    \t{\n    \t\tPurchaseContractId = x.PurchaseContractId,\n    \t\tPurchaseContractLineId = x.Id,\n    \t\tExpectedKg = x.WeightKg,\n    \t\tDeliveredKg = x.PurchaseShipments.Sum(x => x.WeightKg),\n    \t\tDeliveredBoxes = x.PurchaseShipments.Sum(x => x.Boxes),\n    \t});\n\n\treturn await query.ToListAsync();\n}<\/pre><\/div>\n\n\n\n
See also: <\/p>\n\n\n\n