C Sharp LINQ使用例

C# LINQ使用例

[[C#][C# サンプルコード]]

• 国立国会図書館API

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
using System.Xml;
using System.Xml.Linq;

namespace Book
{
    class Program
    {
        static void Main(string[] args)
        {
            var p = new Program();
            if (args.Length < 2)
            {
                Console.WriteLine("must 2 arguments.");
                return;
            }
            string option = args[0];

            string xml = null;
            if (option == "-f")
            {
                xml = File.ReadAllText(args[1],Encoding.UTF8);
            }
            else if (option == "-k")
            {
                var param = new List<KeyValuePair<string, string>>();
                for (int i=1; i<args.Length; i++)
                {
                    string[] kv = args[i].Split('=');
                    param.Add(new KeyValuePair<string, string>(kv[0], kv?[1]));
                }
                xml = p.GetXml(param);
            }
            else if (option == "-t")
            {
                var param = new List<KeyValuePair<string, string>>();
                param.Add(new KeyValuePair<string, string>("title", "Python"));
                xml = p.GetXml(param);
            }
            var books = ParseXml(xml);

            LinqTest(books);
        }

        private static void LinqTest(List<Book> books)
        {

            // QueryExp(books);
            MethodExp(books);

        }

        /// <summary>
        /// メソッド構文
        /// </summary>
        /// <param name="books"></param>
        private static void MethodExp(List<Book> books)
        {
            var result = books
                        .Where( book => book.Title.IndexOf("計算") > 0 )
                        .OrderByDescending( book=> book.Title)
                        .Select( book => book.Title)

             ;

            foreach (string title in result)
            {
                Console.WriteLine(title);
            }
        }

        /// <summary>
        /// クエリ構文
        /// </summary>
        /// <param name="books"></param>
        private static void QueryExp(List<Book> books)
        {
            var result = from book in books
                         where book.Title.IndexOf("計算") > 0
                         orderby book.Title descending
                         select book.Title
             ;

            // 遅延評価
            // books.ForEach(book => book.Title = book.Title.Replace("Python", "HOGE"));

            foreach (string title in result)
            {
                Console.WriteLine(title);
            }
        }

        private static List<Book> ParseXml(string xml)
        {
            XNamespace xmlns = "http://www.loc.gov/zing/srw/";
            XNamespace xmlns2 = "info:srw/schema/1/dc-v1.1";
            XNamespace xmlns3 = "http://purl.org/dc/elements/1.1/";
            
            var root = XElement.Load(new XmlTextReader(new StringReader(xml)));

            var records = from record in root.Elements(xmlns + "records")
                                            .Elements(xmlns + "record")
                                            .Elements(xmlns + "recordData")
                                            .Elements(xmlns2 + "dc")
                          select record
                          ;

            var books = new List<Book>();
            foreach (XElement record in records)
            {

                var book = new Book();
                books.Add(book);

                foreach(PropertyInfo field in book.GetType().GetProperties())
                {
                    foreach (var elms in record.Elements(xmlns3 + field.Name.ToLower()))
                    {
                        field.SetMethod?.Invoke(book, new object[] { elms.Value });
                        break;
                    }
                }

            }
            return books;
        }

        class Book
        {
            public string Title { get; set; } = "";
            public string Creator { get; set; } = "";
            public string Subject { get; set; } = "";
            public string Publisher { get; set; } = "";
            public string Language { get; set; } = "";

            public override string ToString()
            {
                var buf = new StringBuilder();
                buf.Append($"{this.GetType().Name}{{");
                foreach(PropertyInfo p in  this.GetType().GetProperties())
                {
                    buf.Append($"{p.Name}={p.GetValue(this)},");
                }

                buf.Append($"}}");
                return buf.ToString();
            }
        }

        public string GetUrl(List<KeyValuePair<string, string>> param)
        {
            string url = "http://iss.ndl.go.jp/api/sru?operation=searchRetrieve&recordPacking=xml&query={0}";
            string qp = string.Join(" OR ",
                param.Select(kvp => WebUtility.UrlEncode(String.Format("{0}=\"{1}\"", kvp.Key, kvp.Value))));
            return string.Format(url, qp);
        }

        public string GetXml(List<KeyValuePair<string, string>> param)
        {
            string url = GetUrl(param);
            
            using (var client = new WebClient())
            {
                using (var reader = new StreamReader(client.OpenRead(url)))
                {
                    string xml = reader.ReadToEnd();
                    Console.WriteLine(xml);
                    return xml;
                }
            }
        }
    }
}