回答編集履歴
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言語指定のミスを修正
test
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@@ -1,135 +1,68 @@
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`DefaultIfEmpty`を使うと、外部結合に相当する挙動にできます。
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```c#
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class Program {
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static void Main(string[] args) {
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Trader[] traders = new Trader[] {
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new Trader() { Id = 1, CompanyNm = "株式会社ABC", Address = "北海道" },
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new Trader() { Id = 2, CompanyNm = "株式会社DEF", Address = "青森" },
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new Trader() { Id = 3, CompanyNm = "株式会社GHI", Address = "秋田" },
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new Trader() { Id = 4, CompanyNm = "株式会社HIJ", Address = "岩手" },
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new Trader() { Id = 5, CompanyNm = "株式会社KLM", Address = "山形" },
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new Trader() { Id = 6, CompanyNm = "株式会社OPQ", Address = "宮城" },
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};
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```lang-c#
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class Program {
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static void Main(string[] args) {
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ItemList[] items = new ItemList[] {
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new
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new ItemList() { Id = 1, Price = 100, ExpiryDate = new DateTime(2000, 4, 1) },
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new
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new ItemList() { Id = 2, Price = 200, ExpiryDate = new DateTime(2005, 5, 1) },
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new
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new ItemList() { Id = 3, Price = 300, ExpiryDate = new DateTime(2010, 6, 1) },
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new
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new ItemList() { Id = 4, Price = 400, ExpiryDate = new DateTime(2015, 7, 1) },
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new
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new ItemList() { Id = 5, Price = 2020, ExpiryDate = new DateTime(2020, 8, 1) }
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new Trader() { Id = 6, CompanyNm = "株式会社OPQ", Address = "宮城" },
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};
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ItemList[] items = new ItemList[] {
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new ItemList() { Id = 1, Price = 100, ExpiryDate = new DateTime(2000, 4, 1) },
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new ItemList() { Id = 2, Price = 200, ExpiryDate = new DateTime(2005, 5, 1) },
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new ItemList() { Id = 3, Price = 300, ExpiryDate = new DateTime(2010, 6, 1) },
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new ItemList() { Id = 4, Price = 400, ExpiryDate = new DateTime(2015, 7, 1) },
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new ItemList() { Id = 5, Price = 2020, ExpiryDate = new DateTime(2020, 8, 1) }
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};
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var result = traders.GroupJoin(
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items,
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trader => trader.Id,
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item => item.Id,
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(trader, item) => new { trader, item })
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.SelectMany(
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o => o.item.DefaultIfEmpty(), // traderに結合されるitemがない場合は、itemをnullにする
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(j, k) => new {
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Id = j.trader.Id,
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CompanyNm = j.trader.CompanyNm,
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Address = j.trader.Address,
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Price = k?.Price, // itemがnullの場合はPrice/ExpiryDateは参照しない
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ExpireDate = k?.ExpiryDate
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}
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);
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foreach (var o in result) {
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Console.WriteLine($"Id={o.Id}, CompanyNm={o.CompanyNm}, Address={o.Address}, Price={o.Price}, ExpireDate={o.ExpireDate}");
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}
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}
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class Trader {
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public int Id { get; set; }
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public string CompanyNm { get; set; }
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public string Address { get; set; }
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}
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class ItemList {
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public int Id { get; set; }
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public int Price { get; set; }
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public DateTime ExpiryDate { get; set; }
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}
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}
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```
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出力。
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```
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Id=1, CompanyNm=株式会社ABC, Address=北海道, Price=100, ExpireDate=00/04/01 0:00:00
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Id=2, CompanyNm=株式会社DEF, Address=青森, Price=200, ExpireDate=05/05/01 0:00:00
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Id=3, CompanyNm=株式会社GHI, Address=秋田, Price=300, ExpireDate=10/06/01 0:00:00
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Id=4, CompanyNm=株式会社HIJ, Address=岩手, Price=400, ExpireDate=15/07/01 0:00:00
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Id=5, CompanyNm=株式会社KLM, Address=山形, Price=2020, ExpireDate=20/08/01 0:00:00
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Id=6, CompanyNm=株式会社OPQ, Address=宮城, Price=, ExpireDate=
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```
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