首页 > 代码库 > Linq Join
Linq Join
1.准备数据源，我这边定义了一个实体，里面包含ID，Name，State
public class NameModel { public int Id { get; set; } public string Name { get; set; } public string State { get; set; } }
List<NameModel> leftName = new List<NameModel>() { new NameModel() {Id=1,Name="我是1",State="4" }, new NameModel() {Id=2,Name="我是2",State="4" }, new NameModel() {Id=3,Name="我是3",State="4" }, new NameModel() {Id=4,Name="我是4",State="4" }, new NameModel() {Id=0,Name="我是新人",State="4" }, new NameModel() {Id=0,Name="我是新人",State="4" } }; List<NameModel> rigthName = new List<NameModel>(){ new NameModel() {Id=1,Name="我是r1",State="4" }, new NameModel() {Id=5,Name="我是R5",State="4" }, new NameModel() {Id=3,Name="我是R3",State="4" }, new NameModel() {Id=7,Name="我是R7",State="4" } };
2.我们来看看将2个集合通过Linq 来个内连接，这边通过2种方式来实现：
var list = from left in leftName join rigth in rigthName on left.Id equals rigth.Id select new { LeftID = left.Id, LeftName = left.Name, RigthID = rigth.Id, RigthName = rigth.Name }; foreach (var l in list) { Console.WriteLine( l.LeftID + "\t\t" + l.LeftName + "\t\t" + l.RigthID + "\t\t" + l.RigthName + "\t\t" ); } Console.ReadKey();
var list = leftName.Join(rigthName, p => p.Id, x => x.Id, (p, x) => new { LeftID = p.Id, LeftName = p.Name, RigthID = x.Id, RigthName = x.Name }); foreach (var l in list) { Console.WriteLine( l.LeftID + "\t\t" + l.LeftName + "\t\t" + l.RigthID + "\t\t" + l.RigthName + "\t\t" ); } Console.ReadKey();
二次运行的结果是一样的，如图
大家都知道链接包含内连和外连，外连又包含了左右连接，那么我们如何通过Linq来实现左右连接呢？这边就需要我们自己去写扩展方法来实现：
这边需要去定义扩展方法：
public static class JoinExtensions { /// <summary> /// 左连接 /// </summary> /// <typeparam name="TSource"></typeparam> /// <typeparam name="TInner"></typeparam> /// <typeparam name="TKey"></typeparam> /// <typeparam name="TResult"></typeparam> /// <param name="source"></param> /// <param name="inner"></param> /// <param name="pk"></param> /// <param name="fk"></param> /// <param name="result"></param> /// <returns></returns> public static IEnumerable<TResult> LeftJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { IEnumerable<TResult> _result = Enumerable.Empty<TResult>(); _result = from s in source join i in inner on pk(s) equals fk(i) into joinData from left in joinData.DefaultIfEmpty() select result(s, left); return _result; } /// <summary> /// 右连接 /// </summary> /// <typeparam name="TSource"></typeparam> /// <typeparam name="TInner"></typeparam> /// <typeparam name="TKey"></typeparam> /// <typeparam name="TResult"></typeparam> /// <param name="source"></param> /// <param name="inner"></param> /// <param name="pk"></param> /// <param name="fk"></param> /// <param name="result"></param> /// <returns></returns> public static IEnumerable<TResult> RightJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { IEnumerable<TResult> _result = Enumerable.Empty<TResult>(); _result = from i in inner join s in source on fk(i) equals pk(s) into joinData from right in joinData.DefaultIfEmpty() select result(right, i); return _result; } /// <summary> /// 合并 /// </summary> /// <typeparam name="TSource"></typeparam> /// <typeparam name="TInner"></typeparam> /// <typeparam name="TKey"></typeparam> /// <typeparam name="TResult"></typeparam> /// <param name="source"></param> /// <param name="inner"></param> /// <param name="pk"></param> /// <param name="fk"></param> /// <param name="result"></param> /// <returns></returns> public static IEnumerable<TResult> FullOuterJoinJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { var left = source.LeftJoin(inner, pk, fk, result).ToList(); var right = source.RightJoin(inner, pk, fk, result).ToList(); return left.Union(right); } }
下面我们就实现下左链接:
var list = leftName.LeftJoin(rigthName, p => p.Id, x => x.Id, (p, x) => new { LeftID = p.Id, LeftName = p.Name, RigthID = x == null ? 0 : x.Id, RigthName = x == null ? "" : x.Name }); foreach (var l in list) { Console.WriteLine( l.LeftID + "\t\t" + l.LeftName + "\t\t" + l.RigthID + "\t\t" + l.RigthName + "\t\t" ); } Console.ReadKey();
Linq Join
声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉： 投诉/举报 工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。